000009212200000031530000041091000006690400011606610001004155FALSE2021Q1--12-31us-gaap:NaturalGasUsRegulatedMemberus-gaap:NaturalGasUsRegulatedMemberP3M9111191111911119111100000921222021-01-012021-03-310000092122so:AlabamaPowerMember2021-01-012021-03-310000092122so:GeorgiaPowerMember2021-01-012021-03-310000092122so:MississippiPowerMember2021-01-012021-03-310000092122so:SouthernPowerMember2021-01-012021-03-310000092122so:SouthernCompanyGasMember2021-01-012021-03-310000092122us-gaap:CommonStockMember2021-01-012021-03-310000092122so:Series2016A5.25JuniorSubordinatedNotesDue2076Member2021-01-012021-03-310000092122so:Series2017B5.25JuniorSubordinatedNotesDue2077Member2021-01-012021-03-310000092122so:TwoThousandNineteenSeriesACorporateUnitsMember2021-01-012021-03-310000092122so:Series2020A4.95JuniorSubordinatedNotesDue2080Member2021-01-012021-03-310000092122so:Series2020C420JuniorSubordinatedNotesDue2060Member2021-01-012021-03-310000092122so:AlabamaPowerMemberso:A5.00SeriesClassAPreferredStockMember2021-01-012021-03-310000092122so:GeorgiaPowerMemberso:Series2017A5.00JuniorSubordinatedNotesDue2077Member2021-01-012021-03-310000092122so:SouthernPowerMemberso:Series2016A1.000SeniorNotesDue2022Member2021-01-012021-03-310000092122so:Series2016B1.850SeniorNotesDue2026Memberso:SouthernPowerMember2021-01-012021-03-31xbrli:shares00000921222021-03-310000092122so:AlabamaPowerMember2021-03-310000092122so:GeorgiaPowerMember2021-03-310000092122so:MississippiPowerMember2021-03-310000092122so:SouthernPowerMember2021-03-310000092122so:SouthernCompanyGasMember2021-03-31iso4217:USD0000092122us-gaap:RetailMember2021-01-012021-03-310000092122us-gaap:RetailMember2020-01-012020-03-310000092122so:WholesaleNonAffiliatesMember2021-01-012021-03-310000092122so:WholesaleNonAffiliatesMember2020-01-012020-03-310000092122so:OtherElectricRevenueMember2021-01-012021-03-310000092122so:OtherElectricRevenueMember2020-01-012020-03-310000092122us-gaap:AlternativeEnergyMember2021-01-012021-03-310000092122us-gaap:AlternativeEnergyMember2020-01-012020-03-310000092122us-gaap:NaturalGasUsRegulatedMember2021-01-012021-03-310000092122us-gaap:NaturalGasUsRegulatedMember2020-01-012020-03-310000092122us-gaap:ProductAndServiceOtherMember2021-01-012021-03-310000092122us-gaap:ProductAndServiceOtherMember2020-01-012020-03-3100000921222020-01-012020-03-310000092122srt:FuelMember2021-01-012021-03-310000092122srt:FuelMember2020-01-012020-03-310000092122us-gaap:ElectricityPurchasedMember2021-01-012021-03-310000092122us-gaap:ElectricityPurchasedMember2020-01-012020-03-31iso4217:USDxbrli:shares00000921222020-12-3100000921222019-12-3100000921222020-03-310000092122us-gaap:CommonStockMember2019-12-310000092122us-gaap:TreasuryStockMember2019-12-310000092122us-gaap:AdditionalPaidInCapitalMember2019-12-310000092122us-gaap:RetainedEarningsMember2019-12-310000092122us-gaap:AccumulatedOtherComprehensiveIncomeMember2019-12-310000092122us-gaap:NoncontrollingInterestMember2019-12-310000092122us-gaap:RetainedEarningsMember2020-01-012020-03-310000092122us-gaap:NoncontrollingInterestMember2020-01-012020-03-310000092122us-gaap:AccumulatedOtherComprehensiveIncomeMember2020-01-012020-03-310000092122us-gaap:CommonStockMember2020-01-012020-03-310000092122us-gaap:AdditionalPaidInCapitalMember2020-01-012020-03-310000092122us-gaap:TreasuryStockMember2020-01-012020-03-310000092122us-gaap:CommonStockMember2020-03-310000092122us-gaap:TreasuryStockMember2020-03-310000092122us-gaap:AdditionalPaidInCapitalMember2020-03-310000092122us-gaap:RetainedEarningsMember2020-03-310000092122us-gaap:AccumulatedOtherComprehensiveIncomeMember2020-03-310000092122us-gaap:NoncontrollingInterestMember2020-03-310000092122us-gaap:CommonStockMember2020-12-310000092122us-gaap:TreasuryStockMember2020-12-310000092122us-gaap:AdditionalPaidInCapitalMember2020-12-310000092122us-gaap:RetainedEarningsMember2020-12-310000092122us-gaap:AccumulatedOtherComprehensiveIncomeMember2020-12-310000092122us-gaap:NoncontrollingInterestMember2020-12-310000092122us-gaap:RetainedEarningsMember2021-01-012021-03-310000092122us-gaap:NoncontrollingInterestMember2021-01-012021-03-310000092122us-gaap:AccumulatedOtherComprehensiveIncomeMember2021-01-012021-03-310000092122us-gaap:CommonStockMember2021-01-012021-03-310000092122us-gaap:AdditionalPaidInCapitalMember2021-01-012021-03-310000092122us-gaap:CommonStockMember2021-03-310000092122us-gaap:TreasuryStockMember2021-03-310000092122us-gaap:AdditionalPaidInCapitalMember2021-03-310000092122us-gaap:RetainedEarningsMember2021-03-310000092122us-gaap:AccumulatedOtherComprehensiveIncomeMember2021-03-310000092122us-gaap:NoncontrollingInterestMember2021-03-310000092122us-gaap:RetailMemberso:AlabamaPowerMember2021-01-012021-03-310000092122us-gaap:RetailMemberso:AlabamaPowerMember2020-01-012020-03-310000092122so:WholesaleNonAffiliatesMemberso:AlabamaPowerMember2021-01-012021-03-310000092122so:WholesaleNonAffiliatesMemberso:AlabamaPowerMember2020-01-012020-03-310000092122so:AlabamaPowerMemberso:WholesaleAffiliatesMember2021-01-012021-03-310000092122so:AlabamaPowerMemberso:WholesaleAffiliatesMember2020-01-012020-03-310000092122so:AlabamaPowerMemberus-gaap:ProductAndServiceOtherMember2021-01-012021-03-310000092122so:AlabamaPowerMemberus-gaap:ProductAndServiceOtherMember2020-01-012020-03-310000092122so:AlabamaPowerMember2020-01-012020-03-310000092122srt:FuelMemberso:AlabamaPowerMember2021-01-012021-03-310000092122srt:FuelMemberso:AlabamaPowerMember2020-01-012020-03-310000092122us-gaap:ElectricityPurchasedMemberso:AlabamaPowerMember2021-01-012021-03-310000092122us-gaap:ElectricityPurchasedMemberso:AlabamaPowerMember2020-01-012020-03-310000092122so:ElectricityPurchasedAffiliatesMemberso:AlabamaPowerMember2021-01-012021-03-310000092122so:ElectricityPurchasedAffiliatesMemberso:AlabamaPowerMember2020-01-012020-03-310000092122so:AlabamaPowerMember2020-12-310000092122so:AlabamaPowerMember2019-12-310000092122so:AlabamaPowerMember2020-03-310000092122us-gaap:CommonStockMemberso:AlabamaPowerMember2019-12-310000092122us-gaap:AdditionalPaidInCapitalMemberso:AlabamaPowerMember2019-12-310000092122so:AlabamaPowerMemberus-gaap:RetainedEarningsMember2019-12-310000092122us-gaap:AccumulatedOtherComprehensiveIncomeMemberso:AlabamaPowerMember2019-12-310000092122so:AlabamaPowerMemberus-gaap:RetainedEarningsMember2020-01-012020-03-310000092122us-gaap:AdditionalPaidInCapitalMemberso:AlabamaPowerMember2020-01-012020-03-310000092122us-gaap:AccumulatedOtherComprehensiveIncomeMemberso:AlabamaPowerMember2020-01-012020-03-310000092122us-gaap:CommonStockMemberso:AlabamaPowerMember2020-03-310000092122us-gaap:AdditionalPaidInCapitalMemberso:AlabamaPowerMember2020-03-310000092122so:AlabamaPowerMemberus-gaap:RetainedEarningsMember2020-03-310000092122us-gaap:AccumulatedOtherComprehensiveIncomeMemberso:AlabamaPowerMember2020-03-310000092122us-gaap:CommonStockMemberso:AlabamaPowerMember2020-12-310000092122us-gaap:AdditionalPaidInCapitalMemberso:AlabamaPowerMember2020-12-310000092122so:AlabamaPowerMemberus-gaap:RetainedEarningsMember2020-12-310000092122us-gaap:AccumulatedOtherComprehensiveIncomeMemberso:AlabamaPowerMember2020-12-310000092122so:AlabamaPowerMemberus-gaap:RetainedEarningsMember2021-01-012021-03-310000092122us-gaap:AdditionalPaidInCapitalMemberso:AlabamaPowerMember2021-01-012021-03-310000092122us-gaap:AccumulatedOtherComprehensiveIncomeMemberso:AlabamaPowerMember2021-01-012021-03-310000092122us-gaap:CommonStockMemberso:AlabamaPowerMember2021-03-310000092122us-gaap:AdditionalPaidInCapitalMemberso:AlabamaPowerMember2021-03-310000092122so:AlabamaPowerMemberus-gaap:RetainedEarningsMember2021-03-310000092122us-gaap:AccumulatedOtherComprehensiveIncomeMemberso:AlabamaPowerMember2021-03-310000092122us-gaap:RetailMemberso:GeorgiaPowerMember2021-01-012021-03-310000092122us-gaap:RetailMemberso:GeorgiaPowerMember2020-01-012020-03-310000092122so:GeorgiaPowerMemberso:WholesaleNonAffiliatesMember2021-01-012021-03-310000092122so:GeorgiaPowerMemberso:WholesaleNonAffiliatesMember2020-01-012020-03-310000092122so:GeorgiaPowerMemberus-gaap:ProductAndServiceOtherMember2021-01-012021-03-310000092122so:GeorgiaPowerMemberus-gaap:ProductAndServiceOtherMember2020-01-012020-03-310000092122so:GeorgiaPowerMember2020-01-012020-03-310000092122so:GeorgiaPowerMembersrt:FuelMember2021-01-012021-03-310000092122so:GeorgiaPowerMembersrt:FuelMember2020-01-012020-03-310000092122so:GeorgiaPowerMemberus-gaap:ElectricityPurchasedMember2021-01-012021-03-310000092122so:GeorgiaPowerMemberus-gaap:ElectricityPurchasedMember2020-01-012020-03-310000092122so:GeorgiaPowerMemberso:ElectricityPurchasedAffiliatesMember2021-01-012021-03-310000092122so:GeorgiaPowerMemberso:ElectricityPurchasedAffiliatesMember2020-01-012020-03-310000092122so:GeorgiaPowerMember2020-12-310000092122so:GeorgiaPowerMember2019-12-310000092122so:GeorgiaPowerMember2020-03-310000092122so:GeorgiaPowerMemberus-gaap:CommonStockMember2019-12-310000092122so:GeorgiaPowerMemberus-gaap:AdditionalPaidInCapitalMember2019-12-310000092122so:GeorgiaPowerMemberus-gaap:RetainedEarningsMember2019-12-310000092122us-gaap:AccumulatedOtherComprehensiveIncomeMemberso:GeorgiaPowerMember2019-12-310000092122so:GeorgiaPowerMemberus-gaap:RetainedEarningsMember2020-01-012020-03-310000092122so:GeorgiaPowerMemberus-gaap:AdditionalPaidInCapitalMember2020-01-012020-03-310000092122us-gaap:AccumulatedOtherComprehensiveIncomeMemberso:GeorgiaPowerMember2020-01-012020-03-310000092122so:GeorgiaPowerMemberus-gaap:CommonStockMember2020-03-310000092122so:GeorgiaPowerMemberus-gaap:AdditionalPaidInCapitalMember2020-03-310000092122so:GeorgiaPowerMemberus-gaap:RetainedEarningsMember2020-03-310000092122us-gaap:AccumulatedOtherComprehensiveIncomeMemberso:GeorgiaPowerMember2020-03-310000092122so:GeorgiaPowerMemberus-gaap:CommonStockMember2020-12-310000092122so:GeorgiaPowerMemberus-gaap:AdditionalPaidInCapitalMember2020-12-310000092122so:GeorgiaPowerMemberus-gaap:RetainedEarningsMember2020-12-310000092122us-gaap:AccumulatedOtherComprehensiveIncomeMemberso:GeorgiaPowerMember2020-12-310000092122so:GeorgiaPowerMemberus-gaap:RetainedEarningsMember2021-01-012021-03-310000092122so:GeorgiaPowerMemberus-gaap:AdditionalPaidInCapitalMember2021-01-012021-03-310000092122us-gaap:AccumulatedOtherComprehensiveIncomeMemberso:GeorgiaPowerMember2021-01-012021-03-310000092122so:GeorgiaPowerMemberus-gaap:CommonStockMember2021-03-310000092122so:GeorgiaPowerMemberus-gaap:AdditionalPaidInCapitalMember2021-03-310000092122so:GeorgiaPowerMemberus-gaap:RetainedEarningsMember2021-03-310000092122us-gaap:AccumulatedOtherComprehensiveIncomeMemberso:GeorgiaPowerMember2021-03-310000092122us-gaap:RetailMemberso:MississippiPowerMember2021-01-012021-03-310000092122us-gaap:RetailMemberso:MississippiPowerMember2020-01-012020-03-310000092122so:MississippiPowerMemberso:WholesaleNonAffiliatesMember2021-01-012021-03-310000092122so:MississippiPowerMemberso:WholesaleNonAffiliatesMember2020-01-012020-03-310000092122so:MississippiPowerMemberso:WholesaleAffiliatesMember2021-01-012021-03-310000092122so:MississippiPowerMemberso:WholesaleAffiliatesMember2020-01-012020-03-310000092122so:MississippiPowerMemberus-gaap:ProductAndServiceOtherMember2021-01-012021-03-310000092122so:MississippiPowerMemberus-gaap:ProductAndServiceOtherMember2020-01-012020-03-310000092122so:MississippiPowerMember2020-01-012020-03-310000092122so:MississippiPowerMembersrt:FuelMember2021-01-012021-03-310000092122so:MississippiPowerMembersrt:FuelMember2020-01-012020-03-310000092122so:MississippiPowerMemberus-gaap:ElectricityPurchasedMember2021-01-012021-03-310000092122so:MississippiPowerMemberus-gaap:ElectricityPurchasedMember2020-01-012020-03-310000092122so:MississippiPowerMember2020-12-310000092122so:MississippiPowerMember2019-12-310000092122so:MississippiPowerMember2020-03-310000092122so:MississippiPowerMemberus-gaap:CommonStockMember2019-12-310000092122so:MississippiPowerMemberus-gaap:AdditionalPaidInCapitalMember2019-12-310000092122so:MississippiPowerMemberus-gaap:RetainedEarningsMember2019-12-310000092122us-gaap:AccumulatedOtherComprehensiveIncomeMemberso:MississippiPowerMember2019-12-310000092122so:MississippiPowerMemberus-gaap:RetainedEarningsMember2020-01-012020-03-310000092122so:MississippiPowerMemberus-gaap:AdditionalPaidInCapitalMember2020-01-012020-03-310000092122so:MississippiPowerMemberus-gaap:CommonStockMember2020-03-310000092122so:MississippiPowerMemberus-gaap:AdditionalPaidInCapitalMember2020-03-310000092122so:MississippiPowerMemberus-gaap:RetainedEarningsMember2020-03-310000092122us-gaap:AccumulatedOtherComprehensiveIncomeMemberso:MississippiPowerMember2020-03-310000092122so:MississippiPowerMemberus-gaap:CommonStockMember2020-12-310000092122so:MississippiPowerMemberus-gaap:AdditionalPaidInCapitalMember2020-12-310000092122so:MississippiPowerMemberus-gaap:RetainedEarningsMember2020-12-310000092122us-gaap:AccumulatedOtherComprehensiveIncomeMemberso:MississippiPowerMember2020-12-310000092122so:MississippiPowerMemberus-gaap:RetainedEarningsMember2021-01-012021-03-310000092122so:MississippiPowerMemberus-gaap:AdditionalPaidInCapitalMember2021-01-012021-03-310000092122so:MississippiPowerMemberus-gaap:CommonStockMember2021-03-310000092122so:MississippiPowerMemberus-gaap:AdditionalPaidInCapitalMember2021-03-310000092122so:MississippiPowerMemberus-gaap:RetainedEarningsMember2021-03-310000092122us-gaap:AccumulatedOtherComprehensiveIncomeMemberso:MississippiPowerMember2021-03-310000092122so:SouthernPowerMemberso:WholesaleNonAffiliatesMember2021-01-012021-03-310000092122so:SouthernPowerMemberso:WholesaleNonAffiliatesMember2020-01-012020-03-310000092122so:SouthernPowerMemberso:WholesaleAffiliatesMember2021-01-012021-03-310000092122so:SouthernPowerMemberso:WholesaleAffiliatesMember2020-01-012020-03-310000092122so:SouthernPowerMemberus-gaap:ProductAndServiceOtherMember2021-01-012021-03-310000092122so:SouthernPowerMemberus-gaap:ProductAndServiceOtherMember2020-01-012020-03-310000092122so:SouthernPowerMember2020-01-012020-03-310000092122so:SouthernPowerMembersrt:FuelMember2021-01-012021-03-310000092122so:SouthernPowerMembersrt:FuelMember2020-01-012020-03-310000092122us-gaap:ElectricityPurchasedMemberso:SouthernPowerMember2021-01-012021-03-310000092122us-gaap:ElectricityPurchasedMemberso:SouthernPowerMember2020-01-012020-03-310000092122so:SouthernPowerMember2020-12-310000092122so:SouthernPowerMember2019-12-310000092122so:SouthernPowerMember2020-03-310000092122so:SouthernPowerMemberus-gaap:AdditionalPaidInCapitalMember2019-12-310000092122so:SouthernPowerMemberus-gaap:RetainedEarningsMember2019-12-310000092122us-gaap:AccumulatedOtherComprehensiveIncomeMemberso:SouthernPowerMember2019-12-310000092122so:SouthernPowerMemberso:CommonStockholdersEquityNotIncludingNoncontrollingInterestMember2019-12-310000092122us-gaap:NoncontrollingInterestMemberso:SouthernPowerMember2019-12-310000092122so:SouthernPowerMemberus-gaap:RetainedEarningsMember2020-01-012020-03-310000092122so:SouthernPowerMemberso:CommonStockholdersEquityNotIncludingNoncontrollingInterestMember2020-01-012020-03-310000092122us-gaap:NoncontrollingInterestMemberso:SouthernPowerMember2020-01-012020-03-310000092122us-gaap:AccumulatedOtherComprehensiveIncomeMemberso:SouthernPowerMember2020-01-012020-03-310000092122so:SouthernPowerMemberus-gaap:AdditionalPaidInCapitalMember2020-03-310000092122so:SouthernPowerMemberus-gaap:RetainedEarningsMember2020-03-310000092122us-gaap:AccumulatedOtherComprehensiveIncomeMemberso:SouthernPowerMember2020-03-310000092122so:SouthernPowerMemberso:CommonStockholdersEquityNotIncludingNoncontrollingInterestMember2020-03-310000092122us-gaap:NoncontrollingInterestMemberso:SouthernPowerMember2020-03-310000092122so:SouthernPowerMemberus-gaap:AdditionalPaidInCapitalMember2020-12-310000092122so:SouthernPowerMemberus-gaap:RetainedEarningsMember2020-12-310000092122us-gaap:AccumulatedOtherComprehensiveIncomeMemberso:SouthernPowerMember2020-12-310000092122so:SouthernPowerMemberso:CommonStockholdersEquityNotIncludingNoncontrollingInterestMember2020-12-310000092122us-gaap:NoncontrollingInterestMemberso:SouthernPowerMember2020-12-310000092122so:SouthernPowerMemberus-gaap:RetainedEarningsMember2021-01-012021-03-310000092122so:SouthernPowerMemberso:CommonStockholdersEquityNotIncludingNoncontrollingInterestMember2021-01-012021-03-310000092122us-gaap:NoncontrollingInterestMemberso:SouthernPowerMember2021-01-012021-03-310000092122so:SouthernPowerMemberus-gaap:AdditionalPaidInCapitalMember2021-01-012021-03-310000092122us-gaap:AccumulatedOtherComprehensiveIncomeMemberso:SouthernPowerMember2021-01-012021-03-310000092122so:SouthernPowerMemberus-gaap:AdditionalPaidInCapitalMember2021-03-310000092122so:SouthernPowerMemberus-gaap:RetainedEarningsMember2021-03-310000092122us-gaap:AccumulatedOtherComprehensiveIncomeMemberso:SouthernPowerMember2021-03-310000092122so:SouthernPowerMemberso:CommonStockholdersEquityNotIncludingNoncontrollingInterestMember2021-03-310000092122us-gaap:NoncontrollingInterestMemberso:SouthernPowerMember2021-03-310000092122so:SouthernCompanyGasMember2020-01-012020-03-310000092122us-gaap:NaturalGasUsRegulatedMemberso:SouthernCompanyGasMember2021-01-012021-03-310000092122us-gaap:NaturalGasUsRegulatedMemberso:SouthernCompanyGasMember2020-01-012020-03-310000092122us-gaap:AlternativeEnergyMemberso:SouthernCompanyGasMember2021-01-012021-03-310000092122us-gaap:AlternativeEnergyMemberso:SouthernCompanyGasMember2020-01-012020-03-310000092122so:SouthernCompanyGasMember2020-12-310000092122so:SouthernCompanyGasMember2019-12-310000092122so:SouthernCompanyGasMember2020-03-310000092122us-gaap:AdditionalPaidInCapitalMemberso:SouthernCompanyGasMember2019-12-310000092122so:SouthernCompanyGasMemberus-gaap:RetainedEarningsMember2019-12-310000092122us-gaap:AccumulatedOtherComprehensiveIncomeMemberso:SouthernCompanyGasMember2019-12-310000092122so:SouthernCompanyGasMemberus-gaap:RetainedEarningsMember2020-01-012020-03-310000092122us-gaap:AdditionalPaidInCapitalMemberso:SouthernCompanyGasMember2020-01-012020-03-310000092122us-gaap:AccumulatedOtherComprehensiveIncomeMemberso:SouthernCompanyGasMember2020-01-012020-03-310000092122us-gaap:AdditionalPaidInCapitalMemberso:SouthernCompanyGasMember2020-03-310000092122so:SouthernCompanyGasMemberus-gaap:RetainedEarningsMember2020-03-310000092122us-gaap:AccumulatedOtherComprehensiveIncomeMemberso:SouthernCompanyGasMember2020-03-310000092122us-gaap:AdditionalPaidInCapitalMemberso:SouthernCompanyGasMember2020-12-310000092122so:SouthernCompanyGasMemberus-gaap:RetainedEarningsMember2020-12-310000092122us-gaap:AccumulatedOtherComprehensiveIncomeMemberso:SouthernCompanyGasMember2020-12-310000092122so:SouthernCompanyGasMemberus-gaap:RetainedEarningsMember2021-01-012021-03-310000092122us-gaap:AdditionalPaidInCapitalMemberso:SouthernCompanyGasMember2021-01-012021-03-310000092122us-gaap:AccumulatedOtherComprehensiveIncomeMemberso:SouthernCompanyGasMember2021-01-012021-03-310000092122us-gaap:AdditionalPaidInCapitalMemberso:SouthernCompanyGasMember2021-03-310000092122so:SouthernCompanyGasMemberus-gaap:RetainedEarningsMember2021-03-310000092122us-gaap:AccumulatedOtherComprehensiveIncomeMemberso:SouthernCompanyGasMember2021-03-310000092122so:GasDistributionOperationsMemberso:SouthernCompanyGasMember2020-12-310000092122so:GasDistributionOperationsMemberso:SouthernCompanyGasMember2021-03-310000092122so:GasMarketingServicesMemberso:SouthernCompanyGasMember2021-03-310000092122so:GasMarketingServicesMemberso:SouthernCompanyGasMember2020-12-310000092122us-gaap:CustomerRelationshipsMember2021-03-310000092122us-gaap:CustomerRelationshipsMember2020-12-310000092122us-gaap:TradeNamesMember2021-03-310000092122us-gaap:TradeNamesMember2020-12-310000092122so:StorageandTransportationContractsMember2021-03-310000092122so:StorageandTransportationContractsMember2020-12-310000092122so:PPAFairValueAdjustmentsMember2021-03-310000092122so:PPAFairValueAdjustmentsMember2020-12-310000092122us-gaap:OtherIntangibleAssetsMember2021-03-310000092122us-gaap:OtherIntangibleAssetsMember2020-12-310000092122so:SouthernPowerMemberso:PPAFairValueAdjustmentsMember2021-03-310000092122so:SouthernPowerMemberso:PPAFairValueAdjustmentsMember2020-12-310000092122us-gaap:CustomerRelationshipsMemberso:SouthernCompanyGasMember2021-03-310000092122us-gaap:CustomerRelationshipsMemberso:SouthernCompanyGasMember2020-12-310000092122us-gaap:TradeNamesMemberso:SouthernCompanyGasMember2021-03-310000092122us-gaap:TradeNamesMemberso:SouthernCompanyGasMember2020-12-310000092122so:StorageandTransportationContractsMemberso:SouthernCompanyGasMember2021-03-310000092122so:StorageandTransportationContractsMemberso:SouthernCompanyGasMember2020-12-310000092122us-gaap:OtherCurrentAssetsMember2021-03-310000092122us-gaap:OtherCurrentAssetsMember2020-12-310000092122us-gaap:OtherCurrentAssetsMemberso:SouthernPowerMember2021-03-310000092122us-gaap:OtherCurrentAssetsMemberso:SouthernCompanyGasMember2021-03-310000092122us-gaap:OtherCurrentAssetsMemberso:SouthernCompanyGasMember2020-12-310000092122us-gaap:OtherNoncurrentAssetsMember2021-03-310000092122us-gaap:OtherNoncurrentAssetsMember2020-12-310000092122so:SouthernPowerMemberus-gaap:OtherNoncurrentAssetsMember2021-03-310000092122so:SouthernCompanyGasMemberus-gaap:OtherNoncurrentAssetsMember2021-03-310000092122so:SouthernCompanyGasMemberus-gaap:OtherNoncurrentAssetsMember2020-12-310000092122so:OtherRegulatoryLiabilitiesCurrentMemberso:AlabamaPowerMember2021-03-310000092122so:OtherRegulatoryLiabilitiesCurrentMemberso:AlabamaPowerMember2020-12-310000092122so:DeferredUnderRecoveredRegulatoryClauseRevenuesMemberso:AlabamaPowerMember2021-03-310000092122so:DeferredUnderRecoveredRegulatoryClauseRevenuesMemberso:AlabamaPowerMember2020-12-310000092122so:OtherRegulatoryLiabilitiesDeferredMemberso:AlabamaPowerMember2021-03-310000092122so:OtherRegulatoryLiabilitiesDeferredMemberso:AlabamaPowerMember2020-12-310000092122so:GeorgiaPowerMemberso:OverRecoveredFuelClauseRevenuesMember2021-03-310000092122so:GeorgiaPowerMemberso:OverRecoveredFuelClauseRevenuesMember2020-12-310000092122so:OverRecoveredRegulatoryClauseLiabilitiesMemberso:MississippiPowerMember2021-03-310000092122so:OverRecoveredRegulatoryClauseLiabilitiesMemberso:MississippiPowerMember2020-12-310000092122so:MississippiPowerMemberso:OtherRegulatoryAssetsCurrentMember2021-03-310000092122so:MississippiPowerMemberso:OtherRegulatoryAssetsCurrentMember2020-12-310000092122so:MississippiPowerMemberso:OtherRegulatoryAssetsDeferredMember2021-03-310000092122so:MississippiPowerMemberso:OtherRegulatoryAssetsDeferredMember2020-12-310000092122so:MississippiPowerMemberso:OtherRegulatoryLiabilitiesDeferredMember2021-03-310000092122so:MississippiPowerMemberso:OtherRegulatoryLiabilitiesDeferredMember2020-12-310000092122so:OtherRegulatoryLiabilitiesMemberso:SouthernCompanyGasMember2021-03-310000092122so:OtherRegulatoryLiabilitiesMemberso:SouthernCompanyGasMember2020-12-310000092122so:OtherRegulatoryAssetsCurrentMemberso:SouthernCompanyGasMember2021-03-310000092122so:OtherRegulatoryAssetsCurrentMemberso:SouthernCompanyGasMember2020-12-310000092122so:OtherRegulatoryAssetsDeferredMemberso:SouthernCompanyGasMember2021-03-310000092122so:OtherRegulatoryAssetsDeferredMemberso:SouthernCompanyGasMember2020-12-310000092122so:PlantBarryUnit8Memberso:AlabamaPowerMember2021-03-31xbrli:pure0000092122so:MississippiPowerMemberus-gaap:SubsequentEventMemberso:AlabamaPowerMemberso:PlantGreeneCountyUnits1And2Member2021-04-150000092122so:GeorgiaPowerMemberso:PlantVogtleUnits3And4Member2021-01-012021-01-010000092122so:GeorgiaPowerMemberso:PlantVogtleUnits3And4Member2021-03-31so:utility0000092122so:GeorgiaPowerMemberso:PlantVogtleUnits3And4Member2012-01-012012-12-31utr:MW0000092122so:GeorgiaPowerMemberso:PlantVogtleUnits3And4Memberso:VogtleOwnersMember2021-01-012021-03-310000092122so:GeorgiaPowerMemberso:PlantVogtleUnits3And4Member2021-01-012021-03-310000092122so:GeorgiaPowerMemberso:TwentyThirdVogtleConstructionMonitoringReportMemberso:PlantVogtleUnits3And4Member2021-03-310000092122so:GeorgiaPowerMemberso:TwentyThirdVogtleConstructionMonitoringReportMemberso:PlantVogtleUnits3And4Member2020-06-300000092122so:GeorgiaPowerMemberso:TwentyThirdVogtleConstructionMonitoringReportMemberso:PlantVogtleUnits3And4Member2021-01-012021-03-310000092122so:GeorgiaPowerMemberso:TwentyThirdVogtleConstructionMonitoringReportMemberso:PlantVogtleUnits3And4Member2020-01-012020-06-300000092122srt:MinimumMemberso:GeorgiaPowerMemberso:PlantVogtleUnits3And4Memberso:COVID19Member2021-01-012021-03-310000092122so:GeorgiaPowerMemberso:PlantVogtleUnits3And4Membersrt:MaximumMemberso:COVID19Member2021-01-012021-03-310000092122srt:MinimumMemberso:GeorgiaPowerMemberso:PlantVogtleUnits3And4Memberso:COVID19Member2021-03-310000092122so:GeorgiaPowerMemberso:PlantVogtleUnits3And4Membersrt:MaximumMemberso:COVID19Member2021-03-310000092122so:GeorgiaPowerMemberso:PlantVogtleUnits3And4Member2018-08-310000092122so:GeorgiaPowerMemberso:PlantVogtleUnits3And4Memberso:CategoryIMember2021-03-310000092122so:GeorgiaPowerMemberso:PlantVogtleUnits3And4Memberso:CategoryIMember2021-01-012021-03-310000092122so:GeorgiaPowerMemberso:PlantVogtleUnits3And4Memberso:CategoryIIMember2021-01-012021-03-310000092122srt:MinimumMemberso:GeorgiaPowerMemberso:PlantVogtleUnits3And4Memberso:CategoryIIMember2021-01-012021-03-310000092122so:GeorgiaPowerMemberso:PlantVogtleUnits3And4Memberso:CategoryIIMembersrt:MaximumMember2021-01-012021-03-310000092122so:GeorgiaPowerMemberso:PlantVogtleUnits3And4Memberso:CategoryIIMemberso:VogtleOwnersMember2021-01-012021-03-310000092122so:GeorgiaPowerMemberso:CategoryIIIMemberso:PlantVogtleUnits3And4Member2021-01-012021-03-310000092122so:GeorgiaPowerMemberso:CategoryIIIMemberso:PlantVogtleUnits3And4Membersrt:MaximumMember2021-01-012021-03-310000092122so:GeorgiaPowerMemberso:CategoryIIIMemberso:PlantVogtleUnits3And4Memberso:VogtleOwnersMember2021-01-012021-03-310000092122so:GeorgiaPowerMemberso:PlantVogtleUnits3And4Member2009-01-012009-12-310000092122so:GeorgiaPowerMemberso:PlantVogtleUnits3And4Member2018-01-110000092122so:GeorgiaPowerMemberso:PlantVogtleUnits3And4Member2020-11-012020-11-300000092122so:GeorgiaPowerMemberso:PlantVogtleUnits3And4Member2018-01-112018-01-110000092122so:GeorgiaPowerMemberso:PlantVogtleUnits3And4Member2013-12-310000092122so:GeorgiaPowerMemberso:PlantVogtleUnits3And4Member2016-01-012016-01-010000092122so:GeorgiaPowerMemberso:PlantVogtleUnits3And4Member2020-01-012020-01-010000092122so:GeorgiaPowerMemberso:PlantVogtleUnits3And4Member2020-01-012020-12-310000092122so:GeorgiaPowerMemberso:PlantVogtleUnits3And4Membersrt:ScenarioForecastMember2021-01-012021-12-310000092122so:GeorgiaPowerMemberso:PlantVogtleUnits3And4Membersrt:ScenarioForecastMember2022-01-012022-12-31so:report0000092122so:GeorgiaPowerMemberso:TwentyThirdVogtleConstructionMonitoringReportMemberso:PlantVogtleUnits3And4Member2020-12-310000092122so:TwentyFourthVogtleConstructionMonitoringReportMemberso:GeorgiaPowerMemberso:PlantVogtleUnits3And4Member2020-08-312020-08-310000092122so:MississippiPowerMember2021-03-152021-03-150000092122so:MississippiPowerMemberus-gaap:SubsequentEventMemberso:PlantWatsonUnit4Member2021-04-150000092122so:MississippiPowerMemberus-gaap:SubsequentEventMemberso:PlantGreeneCountyUnits1And2Member2021-04-150000092122so:PlantDanielUnits1And2Memberso:MississippiPowerMemberus-gaap:SubsequentEventMember2021-04-150000092122so:PlantDanielUnits1And2Memberso:MississippiPowerMember2021-03-310000092122so:MississippiPowerMemberus-gaap:SubsequentEventMember2021-04-062021-04-060000092122so:InvestingInIllinoisMemberso:SouthernCompanyGasMember2021-01-012021-03-310000092122so:SAVEMemberso:SouthernCompanyGasMember2021-01-012021-03-310000092122so:AtlantaGasLightMemberus-gaap:SubsequentEventMember2021-04-282021-04-280000092122srt:MinimumMemberso:AtlantaGasLightMemberus-gaap:SubsequentEventMember2021-04-280000092122so:AtlantaGasLightMembersrt:MaximumMemberus-gaap:SubsequentEventMember2021-04-28utr:mi0000092122us-gaap:SubsequentEventMemberso:VirginiaNaturalGasMember2021-04-06so:claim0000092122so:ShareholderDerivativeLawsuitsMemberus-gaap:PendingLitigationMember2017-12-310000092122so:ShareholderDerivativeLawsuitsMemberus-gaap:PendingLitigationMember2018-01-012018-12-31so:plaintiff0000092122so:MississippiPowerMemberso:PurportedViolationsOfMississippiConsumerProtectionActMemberus-gaap:PendingLitigationMember2018-01-012018-12-31so:defendant0000092122so:MississippiPowerMemberso:PurportedViolationsOfMississippiConsumerProtectionActMemberus-gaap:PendingLitigationMember2019-03-012019-03-310000092122so:PennEastPipelineMemberso:SouthernCompanyGasMember2021-03-310000092122so:SNGMemberso:SouthernCompanyGasMember2021-03-310000092122so:SNGMember2021-03-310000092122so:RetailElectricResidentialMember2021-01-012021-03-310000092122so:RetailElectricResidentialMemberso:AlabamaPowerMember2021-01-012021-03-310000092122so:GeorgiaPowerMemberso:RetailElectricResidentialMember2021-01-012021-03-310000092122so:RetailElectricResidentialMemberso:MississippiPowerMember2021-01-012021-03-310000092122so:RetailElectricResidentialMemberso:SouthernPowerMember2021-01-012021-03-310000092122so:RetailElectricResidentialMemberso:SouthernCompanyGasMember2021-01-012021-03-310000092122so:RetailElectricCommercialMember2021-01-012021-03-310000092122so:RetailElectricCommercialMemberso:AlabamaPowerMember2021-01-012021-03-310000092122so:GeorgiaPowerMemberso:RetailElectricCommercialMember2021-01-012021-03-310000092122so:MississippiPowerMemberso:RetailElectricCommercialMember2021-01-012021-03-310000092122so:RetailElectricCommercialMemberso:SouthernPowerMember2021-01-012021-03-310000092122so:RetailElectricCommercialMemberso:SouthernCompanyGasMember2021-01-012021-03-310000092122so:RetailElectricIndustrialMember2021-01-012021-03-310000092122so:RetailElectricIndustrialMemberso:AlabamaPowerMember2021-01-012021-03-310000092122so:GeorgiaPowerMemberso:RetailElectricIndustrialMember2021-01-012021-03-310000092122so:MississippiPowerMemberso:RetailElectricIndustrialMember2021-01-012021-03-310000092122so:SouthernPowerMemberso:RetailElectricIndustrialMember2021-01-012021-03-310000092122so:RetailElectricIndustrialMemberso:SouthernCompanyGasMember2021-01-012021-03-310000092122so:RetailElectricOtherMember2021-01-012021-03-310000092122so:RetailElectricOtherMemberso:AlabamaPowerMember2021-01-012021-03-310000092122so:GeorgiaPowerMemberso:RetailElectricOtherMember2021-01-012021-03-310000092122so:MississippiPowerMemberso:RetailElectricOtherMember2021-01-012021-03-310000092122so:RetailElectricOtherMemberso:SouthernPowerMember2021-01-012021-03-310000092122so:RetailElectricOtherMemberso:SouthernCompanyGasMember2021-01-012021-03-310000092122so:RetailElectricMember2021-01-012021-03-310000092122so:RetailElectricMemberso:AlabamaPowerMember2021-01-012021-03-310000092122so:GeorgiaPowerMemberso:RetailElectricMember2021-01-012021-03-310000092122so:RetailElectricMemberso:MississippiPowerMember2021-01-012021-03-310000092122so:RetailElectricMemberso:SouthernPowerMember2021-01-012021-03-310000092122so:RetailElectricMemberso:SouthernCompanyGasMember2021-01-012021-03-310000092122so:NaturalGasDistributionResidentialMember2021-01-012021-03-310000092122so:AlabamaPowerMemberso:NaturalGasDistributionResidentialMember2021-01-012021-03-310000092122so:GeorgiaPowerMemberso:NaturalGasDistributionResidentialMember2021-01-012021-03-310000092122so:MississippiPowerMemberso:NaturalGasDistributionResidentialMember2021-01-012021-03-310000092122so:SouthernPowerMemberso:NaturalGasDistributionResidentialMember2021-01-012021-03-310000092122so:NaturalGasDistributionResidentialMemberso:SouthernCompanyGasMember2021-01-012021-03-310000092122so:NaturalGasDistributionCommercialMember2021-01-012021-03-310000092122so:NaturalGasDistributionCommercialMemberso:AlabamaPowerMember2021-01-012021-03-310000092122so:GeorgiaPowerMemberso:NaturalGasDistributionCommercialMember2021-01-012021-03-310000092122so:MississippiPowerMemberso:NaturalGasDistributionCommercialMember2021-01-012021-03-310000092122so:NaturalGasDistributionCommercialMemberso:SouthernPowerMember2021-01-012021-03-310000092122so:NaturalGasDistributionCommercialMemberso:SouthernCompanyGasMember2021-01-012021-03-310000092122so:NaturalGasDistributionTransportationMember2021-01-012021-03-310000092122so:AlabamaPowerMemberso:NaturalGasDistributionTransportationMember2021-01-012021-03-310000092122so:GeorgiaPowerMemberso:NaturalGasDistributionTransportationMember2021-01-012021-03-310000092122so:MississippiPowerMemberso:NaturalGasDistributionTransportationMember2021-01-012021-03-310000092122so:SouthernPowerMemberso:NaturalGasDistributionTransportationMember2021-01-012021-03-310000092122so:SouthernCompanyGasMemberso:NaturalGasDistributionTransportationMember2021-01-012021-03-310000092122so:NaturalGasDistributionIndustrialMember2021-01-012021-03-310000092122so:NaturalGasDistributionIndustrialMemberso:AlabamaPowerMember2021-01-012021-03-310000092122so:GeorgiaPowerMemberso:NaturalGasDistributionIndustrialMember2021-01-012021-03-310000092122so:MississippiPowerMemberso:NaturalGasDistributionIndustrialMember2021-01-012021-03-310000092122so:NaturalGasDistributionIndustrialMemberso:SouthernPowerMember2021-01-012021-03-310000092122so:NaturalGasDistributionIndustrialMemberso:SouthernCompanyGasMember2021-01-012021-03-310000092122so:NaturalGasDistributionOtherMember2021-01-012021-03-310000092122so:NaturalGasDistributionOtherMemberso:AlabamaPowerMember2021-01-012021-03-310000092122so:NaturalGasDistributionOtherMemberso:GeorgiaPowerMember2021-01-012021-03-310000092122so:NaturalGasDistributionOtherMemberso:MississippiPowerMember2021-01-012021-03-310000092122so:NaturalGasDistributionOtherMemberso:SouthernPowerMember2021-01-012021-03-310000092122so:NaturalGasDistributionOtherMemberso:SouthernCompanyGasMember2021-01-012021-03-310000092122so:NaturalGasDistributionMember2021-01-012021-03-310000092122so:NaturalGasDistributionMemberso:AlabamaPowerMember2021-01-012021-03-310000092122so:GeorgiaPowerMemberso:NaturalGasDistributionMember2021-01-012021-03-310000092122so:MississippiPowerMemberso:NaturalGasDistributionMember2021-01-012021-03-310000092122so:NaturalGasDistributionMemberso:SouthernPowerMember2021-01-012021-03-310000092122so:NaturalGasDistributionMemberso:SouthernCompanyGasMember2021-01-012021-03-310000092122so:WholesaleElectricPPAEnergyRevenuesMember2021-01-012021-03-310000092122so:AlabamaPowerMemberso:WholesaleElectricPPAEnergyRevenuesMember2021-01-012021-03-310000092122so:GeorgiaPowerMemberso:WholesaleElectricPPAEnergyRevenuesMember2021-01-012021-03-310000092122so:MississippiPowerMemberso:WholesaleElectricPPAEnergyRevenuesMember2021-01-012021-03-310000092122so:SouthernPowerMemberso:WholesaleElectricPPAEnergyRevenuesMember2021-01-012021-03-310000092122so:SouthernCompanyGasMemberso:WholesaleElectricPPAEnergyRevenuesMember2021-01-012021-03-310000092122so:WholesaleElectricPPACapacityRevenuesMember2021-01-012021-03-310000092122so:WholesaleElectricPPACapacityRevenuesMemberso:AlabamaPowerMember2021-01-012021-03-310000092122so:GeorgiaPowerMemberso:WholesaleElectricPPACapacityRevenuesMember2021-01-012021-03-310000092122so:MississippiPowerMemberso:WholesaleElectricPPACapacityRevenuesMember2021-01-012021-03-310000092122so:WholesaleElectricPPACapacityRevenuesMemberso:SouthernPowerMember2021-01-012021-03-310000092122so:WholesaleElectricPPACapacityRevenuesMemberso:SouthernCompanyGasMember2021-01-012021-03-310000092122so:WholesaleElectricNonPPARevenuesMember2021-01-012021-03-310000092122so:AlabamaPowerMemberso:WholesaleElectricNonPPARevenuesMember2021-01-012021-03-310000092122so:GeorgiaPowerMemberso:WholesaleElectricNonPPARevenuesMember2021-01-012021-03-310000092122so:MississippiPowerMemberso:WholesaleElectricNonPPARevenuesMember2021-01-012021-03-310000092122so:SouthernPowerMemberso:WholesaleElectricNonPPARevenuesMember2021-01-012021-03-310000092122so:SouthernCompanyGasMemberso:WholesaleElectricNonPPARevenuesMember2021-01-012021-03-310000092122so:WholesaleElectricRevenuesMember2021-01-012021-03-310000092122so:WholesaleElectricRevenuesMemberso:AlabamaPowerMember2021-01-012021-03-310000092122so:GeorgiaPowerMemberso:WholesaleElectricRevenuesMember2021-01-012021-03-310000092122so:MississippiPowerMemberso:WholesaleElectricRevenuesMember2021-01-012021-03-310000092122so:SouthernPowerMemberso:WholesaleElectricRevenuesMember2021-01-012021-03-310000092122so:WholesaleElectricRevenuesMemberso:SouthernCompanyGasMember2021-01-012021-03-310000092122so:OtherNaturalGasWholesaleGasServicesMember2021-01-012021-03-310000092122so:OtherNaturalGasWholesaleGasServicesMemberso:AlabamaPowerMember2021-01-012021-03-310000092122so:GeorgiaPowerMemberso:OtherNaturalGasWholesaleGasServicesMember2021-01-012021-03-310000092122so:MississippiPowerMemberso:OtherNaturalGasWholesaleGasServicesMember2021-01-012021-03-310000092122so:SouthernPowerMemberso:OtherNaturalGasWholesaleGasServicesMember2021-01-012021-03-310000092122so:OtherNaturalGasWholesaleGasServicesMemberso:SouthernCompanyGasMember2021-01-012021-03-310000092122so:OtherNaturalGasGasMarketingServicesMember2021-01-012021-03-310000092122so:OtherNaturalGasGasMarketingServicesMemberso:AlabamaPowerMember2021-01-012021-03-310000092122so:OtherNaturalGasGasMarketingServicesMemberso:GeorgiaPowerMember2021-01-012021-03-310000092122so:OtherNaturalGasGasMarketingServicesMemberso:MississippiPowerMember2021-01-012021-03-310000092122so:OtherNaturalGasGasMarketingServicesMemberso:SouthernPowerMember2021-01-012021-03-310000092122so:OtherNaturalGasGasMarketingServicesMemberso:SouthernCompanyGasMember2021-01-012021-03-310000092122so:OtherNaturalGasOtherNaturalGasRevenuesMember2021-01-012021-03-310000092122so:OtherNaturalGasOtherNaturalGasRevenuesMemberso:AlabamaPowerMember2021-01-012021-03-310000092122so:GeorgiaPowerMemberso:OtherNaturalGasOtherNaturalGasRevenuesMember2021-01-012021-03-310000092122so:MississippiPowerMemberso:OtherNaturalGasOtherNaturalGasRevenuesMember2021-01-012021-03-310000092122so:SouthernPowerMemberso:OtherNaturalGasOtherNaturalGasRevenuesMember2021-01-012021-03-310000092122so:OtherNaturalGasOtherNaturalGasRevenuesMemberso:SouthernCompanyGasMember2021-01-012021-03-310000092122so:OtherNaturalGasMember2021-01-012021-03-310000092122so:OtherNaturalGasMemberso:AlabamaPowerMember2021-01-012021-03-310000092122so:GeorgiaPowerMemberso:OtherNaturalGasMember2021-01-012021-03-310000092122so:MississippiPowerMemberso:OtherNaturalGasMember2021-01-012021-03-310000092122so:OtherNaturalGasMemberso:SouthernPowerMember2021-01-012021-03-310000092122so:OtherNaturalGasMemberso:SouthernCompanyGasMember2021-01-012021-03-310000092122so:OtherRevenuesMember2021-01-012021-03-310000092122so:AlabamaPowerMemberso:OtherRevenuesMember2021-01-012021-03-310000092122so:GeorgiaPowerMemberso:OtherRevenuesMember2021-01-012021-03-310000092122so:MississippiPowerMemberso:OtherRevenuesMember2021-01-012021-03-310000092122so:SouthernPowerMemberso:OtherRevenuesMember2021-01-012021-03-310000092122so:SouthernCompanyGasMemberso:OtherRevenuesMember2021-01-012021-03-310000092122so:OtherRevenueSourcesMember2021-01-012021-03-310000092122so:AlabamaPowerMemberso:OtherRevenueSourcesMember2021-01-012021-03-310000092122so:GeorgiaPowerMemberso:OtherRevenueSourcesMember2021-01-012021-03-310000092122so:MississippiPowerMemberso:OtherRevenueSourcesMember2021-01-012021-03-310000092122so:SouthernPowerMemberso:OtherRevenueSourcesMember2021-01-012021-03-310000092122so:OtherRevenueSourcesMemberso:SouthernCompanyGasMember2021-01-012021-03-310000092122so:OtherAdjustmentsMember2021-01-012021-03-310000092122so:AlabamaPowerMemberso:OtherAdjustmentsMember2021-01-012021-03-310000092122so:GeorgiaPowerMemberso:OtherAdjustmentsMember2021-01-012021-03-310000092122so:MississippiPowerMemberso:OtherAdjustmentsMember2021-01-012021-03-310000092122so:SouthernPowerMemberso:OtherAdjustmentsMember2021-01-012021-03-310000092122so:SouthernCompanyGasMemberso:OtherAdjustmentsMember2021-01-012021-03-310000092122so:RetailElectricResidentialMember2020-01-012020-03-310000092122so:RetailElectricResidentialMemberso:AlabamaPowerMember2020-01-012020-03-310000092122so:GeorgiaPowerMemberso:RetailElectricResidentialMember2020-01-012020-03-310000092122so:RetailElectricResidentialMemberso:MississippiPowerMember2020-01-012020-03-310000092122so:RetailElectricResidentialMemberso:SouthernPowerMember2020-01-012020-03-310000092122so:RetailElectricResidentialMemberso:SouthernCompanyGasMember2020-01-012020-03-310000092122so:RetailElectricCommercialMember2020-01-012020-03-310000092122so:RetailElectricCommercialMemberso:AlabamaPowerMember2020-01-012020-03-310000092122so:GeorgiaPowerMemberso:RetailElectricCommercialMember2020-01-012020-03-310000092122so:MississippiPowerMemberso:RetailElectricCommercialMember2020-01-012020-03-310000092122so:RetailElectricCommercialMemberso:SouthernPowerMember2020-01-012020-03-310000092122so:RetailElectricCommercialMemberso:SouthernCompanyGasMember2020-01-012020-03-310000092122so:RetailElectricIndustrialMember2020-01-012020-03-310000092122so:RetailElectricIndustrialMemberso:AlabamaPowerMember2020-01-012020-03-310000092122so:GeorgiaPowerMemberso:RetailElectricIndustrialMember2020-01-012020-03-310000092122so:MississippiPowerMemberso:RetailElectricIndustrialMember2020-01-012020-03-310000092122so:SouthernPowerMemberso:RetailElectricIndustrialMember2020-01-012020-03-310000092122so:RetailElectricIndustrialMemberso:SouthernCompanyGasMember2020-01-012020-03-310000092122so:RetailElectricOtherMember2020-01-012020-03-310000092122so:RetailElectricOtherMemberso:AlabamaPowerMember2020-01-012020-03-310000092122so:GeorgiaPowerMemberso:RetailElectricOtherMember2020-01-012020-03-310000092122so:MississippiPowerMemberso:RetailElectricOtherMember2020-01-012020-03-310000092122so:RetailElectricOtherMemberso:SouthernPowerMember2020-01-012020-03-310000092122so:RetailElectricOtherMemberso:SouthernCompanyGasMember2020-01-012020-03-310000092122so:RetailElectricMember2020-01-012020-03-310000092122so:RetailElectricMemberso:AlabamaPowerMember2020-01-012020-03-310000092122so:GeorgiaPowerMemberso:RetailElectricMember2020-01-012020-03-310000092122so:RetailElectricMemberso:MississippiPowerMember2020-01-012020-03-310000092122so:RetailElectricMemberso:SouthernPowerMember2020-01-012020-03-310000092122so:RetailElectricMemberso:SouthernCompanyGasMember2020-01-012020-03-310000092122so:NaturalGasDistributionResidentialMember2020-01-012020-03-310000092122so:AlabamaPowerMemberso:NaturalGasDistributionResidentialMember2020-01-012020-03-310000092122so:GeorgiaPowerMemberso:NaturalGasDistributionResidentialMember2020-01-012020-03-310000092122so:MississippiPowerMemberso:NaturalGasDistributionResidentialMember2020-01-012020-03-310000092122so:SouthernPowerMemberso:NaturalGasDistributionResidentialMember2020-01-012020-03-310000092122so:NaturalGasDistributionResidentialMemberso:SouthernCompanyGasMember2020-01-012020-03-310000092122so:NaturalGasDistributionCommercialMember2020-01-012020-03-310000092122so:NaturalGasDistributionCommercialMemberso:AlabamaPowerMember2020-01-012020-03-310000092122so:GeorgiaPowerMemberso:NaturalGasDistributionCommercialMember2020-01-012020-03-310000092122so:MississippiPowerMemberso:NaturalGasDistributionCommercialMember2020-01-012020-03-310000092122so:NaturalGasDistributionCommercialMemberso:SouthernPowerMember2020-01-012020-03-310000092122so:NaturalGasDistributionCommercialMemberso:SouthernCompanyGasMember2020-01-012020-03-310000092122so:NaturalGasDistributionTransportationMember2020-01-012020-03-310000092122so:AlabamaPowerMemberso:NaturalGasDistributionTransportationMember2020-01-012020-03-310000092122so:GeorgiaPowerMemberso:NaturalGasDistributionTransportationMember2020-01-012020-03-310000092122so:MississippiPowerMemberso:NaturalGasDistributionTransportationMember2020-01-012020-03-310000092122so:SouthernPowerMemberso:NaturalGasDistributionTransportationMember2020-01-012020-03-310000092122so:SouthernCompanyGasMemberso:NaturalGasDistributionTransportationMember2020-01-012020-03-310000092122so:NaturalGasDistributionIndustrialMember2020-01-012020-03-310000092122so:NaturalGasDistributionIndustrialMemberso:AlabamaPowerMember2020-01-012020-03-310000092122so:GeorgiaPowerMemberso:NaturalGasDistributionIndustrialMember2020-01-012020-03-310000092122so:MississippiPowerMemberso:NaturalGasDistributionIndustrialMember2020-01-012020-03-310000092122so:NaturalGasDistributionIndustrialMemberso:SouthernPowerMember2020-01-012020-03-310000092122so:NaturalGasDistributionIndustrialMemberso:SouthernCompanyGasMember2020-01-012020-03-310000092122so:NaturalGasDistributionOtherMember2020-01-012020-03-310000092122so:NaturalGasDistributionOtherMemberso:AlabamaPowerMember2020-01-012020-03-310000092122so:NaturalGasDistributionOtherMemberso:GeorgiaPowerMember2020-01-012020-03-310000092122so:NaturalGasDistributionOtherMemberso:MississippiPowerMember2020-01-012020-03-310000092122so:NaturalGasDistributionOtherMemberso:SouthernPowerMember2020-01-012020-03-310000092122so:NaturalGasDistributionOtherMemberso:SouthernCompanyGasMember2020-01-012020-03-310000092122so:NaturalGasDistributionMember2020-01-012020-03-310000092122so:NaturalGasDistributionMemberso:AlabamaPowerMember2020-01-012020-03-310000092122so:GeorgiaPowerMemberso:NaturalGasDistributionMember2020-01-012020-03-310000092122so:MississippiPowerMemberso:NaturalGasDistributionMember2020-01-012020-03-310000092122so:NaturalGasDistributionMemberso:SouthernPowerMember2020-01-012020-03-310000092122so:NaturalGasDistributionMemberso:SouthernCompanyGasMember2020-01-012020-03-310000092122so:WholesaleElectricPPAEnergyRevenuesMember2020-01-012020-03-310000092122so:AlabamaPowerMemberso:WholesaleElectricPPAEnergyRevenuesMember2020-01-012020-03-310000092122so:GeorgiaPowerMemberso:WholesaleElectricPPAEnergyRevenuesMember2020-01-012020-03-310000092122so:MississippiPowerMemberso:WholesaleElectricPPAEnergyRevenuesMember2020-01-012020-03-310000092122so:SouthernPowerMemberso:WholesaleElectricPPAEnergyRevenuesMember2020-01-012020-03-310000092122so:SouthernCompanyGasMemberso:WholesaleElectricPPAEnergyRevenuesMember2020-01-012020-03-310000092122so:WholesaleElectricPPACapacityRevenuesMember2020-01-012020-03-310000092122so:WholesaleElectricPPACapacityRevenuesMemberso:AlabamaPowerMember2020-01-012020-03-310000092122so:GeorgiaPowerMemberso:WholesaleElectricPPACapacityRevenuesMember2020-01-012020-03-310000092122so:MississippiPowerMemberso:WholesaleElectricPPACapacityRevenuesMember2020-01-012020-03-310000092122so:WholesaleElectricPPACapacityRevenuesMemberso:SouthernPowerMember2020-01-012020-03-310000092122so:WholesaleElectricPPACapacityRevenuesMemberso:SouthernCompanyGasMember2020-01-012020-03-310000092122so:WholesaleElectricNonPPARevenuesMember2020-01-012020-03-310000092122so:AlabamaPowerMemberso:WholesaleElectricNonPPARevenuesMember2020-01-012020-03-310000092122so:GeorgiaPowerMemberso:WholesaleElectricNonPPARevenuesMember2020-01-012020-03-310000092122so:MississippiPowerMemberso:WholesaleElectricNonPPARevenuesMember2020-01-012020-03-310000092122so:SouthernPowerMemberso:WholesaleElectricNonPPARevenuesMember2020-01-012020-03-310000092122so:SouthernCompanyGasMemberso:WholesaleElectricNonPPARevenuesMember2020-01-012020-03-310000092122so:WholesaleElectricRevenuesMember2020-01-012020-03-310000092122so:WholesaleElectricRevenuesMemberso:AlabamaPowerMember2020-01-012020-03-310000092122so:GeorgiaPowerMemberso:WholesaleElectricRevenuesMember2020-01-012020-03-310000092122so:MississippiPowerMemberso:WholesaleElectricRevenuesMember2020-01-012020-03-310000092122so:SouthernPowerMemberso:WholesaleElectricRevenuesMember2020-01-012020-03-310000092122so:WholesaleElectricRevenuesMemberso:SouthernCompanyGasMember2020-01-012020-03-310000092122so:OtherNaturalGasWholesaleGasServicesMember2020-01-012020-03-310000092122so:OtherNaturalGasWholesaleGasServicesMemberso:AlabamaPowerMember2020-01-012020-03-310000092122so:GeorgiaPowerMemberso:OtherNaturalGasWholesaleGasServicesMember2020-01-012020-03-310000092122so:MississippiPowerMemberso:OtherNaturalGasWholesaleGasServicesMember2020-01-012020-03-310000092122so:SouthernPowerMemberso:OtherNaturalGasWholesaleGasServicesMember2020-01-012020-03-310000092122so:OtherNaturalGasWholesaleGasServicesMemberso:SouthernCompanyGasMember2020-01-012020-03-310000092122so:OtherNaturalGasGasMarketingServicesMember2020-01-012020-03-310000092122so:OtherNaturalGasGasMarketingServicesMemberso:AlabamaPowerMember2020-01-012020-03-310000092122so:OtherNaturalGasGasMarketingServicesMemberso:GeorgiaPowerMember2020-01-012020-03-310000092122so:OtherNaturalGasGasMarketingServicesMemberso:MississippiPowerMember2020-01-012020-03-310000092122so:OtherNaturalGasGasMarketingServicesMemberso:SouthernPowerMember2020-01-012020-03-310000092122so:OtherNaturalGasGasMarketingServicesMemberso:SouthernCompanyGasMember2020-01-012020-03-310000092122so:OtherNaturalGasOtherNaturalGasRevenuesMember2020-01-012020-03-310000092122so:OtherNaturalGasOtherNaturalGasRevenuesMemberso:AlabamaPowerMember2020-01-012020-03-310000092122so:GeorgiaPowerMemberso:OtherNaturalGasOtherNaturalGasRevenuesMember2020-01-012020-03-310000092122so:MississippiPowerMemberso:OtherNaturalGasOtherNaturalGasRevenuesMember2020-01-012020-03-310000092122so:SouthernPowerMemberso:OtherNaturalGasOtherNaturalGasRevenuesMember2020-01-012020-03-310000092122so:OtherNaturalGasOtherNaturalGasRevenuesMemberso:SouthernCompanyGasMember2020-01-012020-03-310000092122so:OtherNaturalGasMember2020-01-012020-03-310000092122so:OtherNaturalGasMemberso:AlabamaPowerMember2020-01-012020-03-310000092122so:GeorgiaPowerMemberso:OtherNaturalGasMember2020-01-012020-03-310000092122so:MississippiPowerMemberso:OtherNaturalGasMember2020-01-012020-03-310000092122so:OtherNaturalGasMemberso:SouthernPowerMember2020-01-012020-03-310000092122so:OtherNaturalGasMemberso:SouthernCompanyGasMember2020-01-012020-03-310000092122so:OtherRevenuesMember2020-01-012020-03-310000092122so:AlabamaPowerMemberso:OtherRevenuesMember2020-01-012020-03-310000092122so:GeorgiaPowerMemberso:OtherRevenuesMember2020-01-012020-03-310000092122so:MississippiPowerMemberso:OtherRevenuesMember2020-01-012020-03-310000092122so:SouthernPowerMemberso:OtherRevenuesMember2020-01-012020-03-310000092122so:SouthernCompanyGasMemberso:OtherRevenuesMember2020-01-012020-03-310000092122so:OtherRevenueSourcesMember2020-01-012020-03-310000092122so:AlabamaPowerMemberso:OtherRevenueSourcesMember2020-01-012020-03-310000092122so:GeorgiaPowerMemberso:OtherRevenueSourcesMember2020-01-012020-03-310000092122so:MississippiPowerMemberso:OtherRevenueSourcesMember2020-01-012020-03-310000092122so:SouthernPowerMemberso:OtherRevenueSourcesMember2020-01-012020-03-310000092122so:OtherRevenueSourcesMemberso:SouthernCompanyGasMember2020-01-012020-03-310000092122so:OtherAdjustmentsMember2020-01-012020-03-310000092122so:AlabamaPowerMemberso:OtherAdjustmentsMember2020-01-012020-03-310000092122so:GeorgiaPowerMemberso:OtherAdjustmentsMember2020-01-012020-03-310000092122so:MississippiPowerMemberso:OtherAdjustmentsMember2020-01-012020-03-310000092122so:SouthernPowerMemberso:OtherAdjustmentsMember2020-01-012020-03-310000092122so:SouthernCompanyGasMemberso:OtherAdjustmentsMember2020-01-012020-03-310000092122so:UnregulatedDistributedGenerationMember2021-03-310000092122so:UnregulatedDistributedGenerationMember2020-12-3100000921222021-04-012021-03-3100000921222022-01-012021-03-3100000921222023-01-012021-03-3100000921222024-01-012021-03-3100000921222025-01-012021-03-3100000921222026-01-012021-03-310000092122so:AlabamaPowerMember2021-04-012021-03-3100000921222022-01-01so:AlabamaPowerMember2021-03-3100000921222023-01-01so:AlabamaPowerMember2021-03-3100000921222024-01-01so:AlabamaPowerMember2021-03-310000092122so:AlabamaPowerMember2025-01-012021-03-3100000921222026-01-01so:AlabamaPowerMember2021-03-310000092122so:GeorgiaPowerMember2021-04-012021-03-310000092122so:GeorgiaPowerMember2022-01-012021-03-310000092122so:GeorgiaPowerMember2023-01-012021-03-310000092122so:GeorgiaPowerMember2024-01-012021-03-310000092122so:GeorgiaPowerMember2025-01-012021-03-310000092122so:GeorgiaPowerMember2026-01-012021-03-310000092122so:SouthernPowerMember2021-04-012021-03-3100000921222022-01-01so:SouthernPowerMember2021-03-310000092122so:SouthernPowerMember2023-01-012021-03-3100000921222024-01-01so:SouthernPowerMember2021-03-310000092122so:SouthernPowerMember2025-01-012021-03-310000092122so:SouthernPowerMember2026-01-012021-03-310000092122so:SPSolarHoldingsILPMemberso:SouthernPowerMemberus-gaap:VariableInterestEntityPrimaryBeneficiaryMember2021-03-310000092122so:SPSolarHoldingsILPMemberso:SouthernPowerMemberus-gaap:VariableInterestEntityPrimaryBeneficiaryMember2020-12-310000092122so:SPSolarHoldingsILPMemberso:SouthernPowerMember2021-01-012021-03-310000092122so:SPSolarHoldingsILPMemberso:GlobalAtlanticMember2021-01-012021-03-310000092122so:SPWindMemberso:SouthernPowerMemberus-gaap:VariableInterestEntityPrimaryBeneficiaryMember2021-03-310000092122so:SPWindMemberso:SouthernPowerMemberus-gaap:VariableInterestEntityPrimaryBeneficiaryMember2020-12-310000092122so:SPWindMemberso:SouthernPowerMemberus-gaap:VariableInterestEntityPrimaryBeneficiaryMember2021-01-012021-03-310000092122so:SPWindMemberus-gaap:VariableInterestEntityPrimaryBeneficiaryMemberso:FinancialInvestorsMember2021-01-012021-03-31so:investor0000092122so:OtherVariableInterestEntitiesMemberso:SouthernPowerMemberus-gaap:VariableInterestEntityPrimaryBeneficiaryMember2021-03-310000092122so:OtherVariableInterestEntitiesMemberso:SouthernPowerMemberus-gaap:VariableInterestEntityPrimaryBeneficiaryMember2020-12-310000092122so:SNGMemberso:SouthernCompanyGasMember2020-12-310000092122so:PennEastPipelineMemberso:SouthernCompanyGasMember2020-12-310000092122so:OtherMemberso:SouthernCompanyGasMember2021-03-310000092122so:OtherMemberso:SouthernCompanyGasMember2020-12-310000092122so:SNGMemberso:SouthernCompanyGasMember2021-01-012021-03-310000092122so:SNGMemberso:SouthernCompanyGasMember2020-01-012020-03-310000092122so:PennEastPipelineMemberso:SouthernCompanyGasMember2021-01-012021-03-310000092122so:PennEastPipelineMemberso:SouthernCompanyGasMember2020-01-012020-03-310000092122so:OtherMemberso:SouthernCompanyGasMember2021-01-012021-03-310000092122so:OtherMemberso:SouthernCompanyGasMember2020-01-012020-03-310000092122so:SouthernCompanyMember2021-03-310000092122so:SouthernElectricGeneratingCompanyMember2021-03-310000092122so:ContinuingLetterOfCreditFacilityAMemberso:SouthernPowerMember2021-03-310000092122so:SouthernPowerMemberso:ContinuingLetterOfCreditFacilityBMember2021-03-310000092122so:SouthernCompanyGasCapitalMember2021-03-310000092122so:NicorGasMember2021-03-310000092122us-gaap:PensionPlansDefinedBenefitMember2021-03-310000092122us-gaap:PensionPlansDefinedBenefitMember2021-01-012021-03-310000092122us-gaap:PensionPlansDefinedBenefitMemberso:AlabamaPowerMember2021-01-012021-03-310000092122so:GeorgiaPowerMemberus-gaap:PensionPlansDefinedBenefitMember2021-01-012021-03-310000092122so:MississippiPowerMemberus-gaap:PensionPlansDefinedBenefitMember2021-01-012021-03-310000092122us-gaap:PensionPlansDefinedBenefitMemberso:SouthernPowerMember2021-01-012021-03-310000092122us-gaap:PensionPlansDefinedBenefitMemberso:SouthernCompanyGasMember2021-01-012021-03-310000092122us-gaap:OtherPostretirementBenefitPlansDefinedBenefitMember2021-01-012021-03-310000092122us-gaap:OtherPostretirementBenefitPlansDefinedBenefitMemberso:AlabamaPowerMember2021-01-012021-03-310000092122so:GeorgiaPowerMemberus-gaap:OtherPostretirementBenefitPlansDefinedBenefitMember2021-01-012021-03-310000092122so:MississippiPowerMemberus-gaap:OtherPostretirementBenefitPlansDefinedBenefitMember2021-01-012021-03-310000092122us-gaap:OtherPostretirementBenefitPlansDefinedBenefitMemberso:SouthernPowerMember2021-01-012021-03-310000092122us-gaap:OtherPostretirementBenefitPlansDefinedBenefitMemberso:SouthernCompanyGasMember2021-01-012021-03-310000092122us-gaap:PensionPlansDefinedBenefitMember2020-01-012020-03-310000092122us-gaap:PensionPlansDefinedBenefitMemberso:AlabamaPowerMember2020-01-012020-03-310000092122so:GeorgiaPowerMemberus-gaap:PensionPlansDefinedBenefitMember2020-01-012020-03-310000092122so:MississippiPowerMemberus-gaap:PensionPlansDefinedBenefitMember2020-01-012020-03-310000092122us-gaap:PensionPlansDefinedBenefitMemberso:SouthernPowerMember2020-01-012020-03-310000092122us-gaap:PensionPlansDefinedBenefitMemberso:SouthernCompanyGasMember2020-01-012020-03-310000092122us-gaap:OtherPostretirementBenefitPlansDefinedBenefitMember2020-01-012020-03-310000092122us-gaap:OtherPostretirementBenefitPlansDefinedBenefitMemberso:AlabamaPowerMember2020-01-012020-03-310000092122so:GeorgiaPowerMemberus-gaap:OtherPostretirementBenefitPlansDefinedBenefitMember2020-01-012020-03-310000092122so:MississippiPowerMemberus-gaap:OtherPostretirementBenefitPlansDefinedBenefitMember2020-01-012020-03-310000092122us-gaap:OtherPostretirementBenefitPlansDefinedBenefitMemberso:SouthernPowerMember2020-01-012020-03-310000092122us-gaap:OtherPostretirementBenefitPlansDefinedBenefitMemberso:SouthernCompanyGasMember2020-01-012020-03-310000092122us-gaap:FairValueMeasurementsRecurringMemberus-gaap:EnergyRelatedDerivativeMemberus-gaap:FairValueInputsLevel1Member2021-03-310000092122us-gaap:FairValueMeasurementsRecurringMemberus-gaap:EnergyRelatedDerivativeMemberus-gaap:FairValueInputsLevel2Member2021-03-310000092122us-gaap:FairValueInputsLevel3Memberus-gaap:FairValueMeasurementsRecurringMemberus-gaap:EnergyRelatedDerivativeMember2021-03-310000092122us-gaap:FairValueMeasurementsRecurringMemberus-gaap:EnergyRelatedDerivativeMember2021-03-310000092122us-gaap:FairValueMeasurementsRecurringMemberus-gaap:InterestRateContractMemberus-gaap:FairValueInputsLevel1Member2021-03-310000092122us-gaap:FairValueMeasurementsRecurringMemberus-gaap:InterestRateContractMemberus-gaap:FairValueInputsLevel2Member2021-03-310000092122us-gaap:FairValueInputsLevel3Memberus-gaap:FairValueMeasurementsRecurringMemberus-gaap:InterestRateContractMember2021-03-310000092122us-gaap:FairValueMeasurementsRecurringMemberus-gaap:InterestRateContractMember2021-03-310000092122us-gaap:FairValueMeasurementsRecurringMemberus-gaap:FairValueInputsLevel1Memberus-gaap:ForeignExchangeContractMember2021-03-310000092122us-gaap:FairValueMeasurementsRecurringMemberus-gaap:FairValueInputsLevel2Memberus-gaap:ForeignExchangeContractMember2021-03-310000092122us-gaap:FairValueInputsLevel3Memberus-gaap:FairValueMeasurementsRecurringMemberus-gaap:ForeignExchangeContractMember2021-03-310000092122us-gaap:FairValueMeasurementsRecurringMemberus-gaap:ForeignExchangeContractMember2021-03-310000092122us-gaap:FairValueMeasurementsRecurringMemberus-gaap:FairValueInputsLevel1Memberso:DomesticEquityMember2021-03-310000092122us-gaap:FairValueMeasurementsRecurringMemberus-gaap:FairValueInputsLevel2Memberso:DomesticEquityMember2021-03-310000092122us-gaap:FairValueInputsLevel3Memberus-gaap:FairValueMeasurementsRecurringMemberso:DomesticEquityMember2021-03-310000092122us-gaap:FairValueMeasurementsRecurringMemberso:DomesticEquityMember2021-03-310000092122us-gaap:FairValueMeasurementsRecurringMemberso:ForeignEquityMemberus-gaap:FairValueInputsLevel1Member2021-03-310000092122us-gaap:FairValueMeasurementsRecurringMemberso:ForeignEquityMemberus-gaap:FairValueInputsLevel2Member2021-03-310000092122us-gaap:FairValueInputsLevel3Memberus-gaap:FairValueMeasurementsRecurringMemberso:ForeignEquityMember2021-03-310000092122us-gaap:FairValueMeasurementsRecurringMemberso:ForeignEquityMember2021-03-310000092122us-gaap:FairValueMeasurementsRecurringMemberus-gaap:USTreasuryAndGovernmentMemberus-gaap:FairValueInputsLevel1Member2021-03-310000092122us-gaap:FairValueMeasurementsRecurringMemberus-gaap:USTreasuryAndGovernmentMemberus-gaap:FairValueInputsLevel2Member2021-03-310000092122us-gaap:FairValueInputsLevel3Memberus-gaap:FairValueMeasurementsRecurringMemberus-gaap:USTreasuryAndGovernmentMember2021-03-310000092122us-gaap:FairValueMeasurementsRecurringMemberus-gaap:USTreasuryAndGovernmentMember2021-03-310000092122us-gaap:FairValueMeasurementsRecurringMemberus-gaap:MunicipalBondsMemberus-gaap:FairValueInputsLevel1Member2021-03-310000092122us-gaap:FairValueMeasurementsRecurringMemberus-gaap:MunicipalBondsMemberus-gaap:FairValueInputsLevel2Member2021-03-310000092122us-gaap:FairValueInputsLevel3Memberus-gaap:FairValueMeasurementsRecurringMemberus-gaap:MunicipalBondsMember2021-03-310000092122us-gaap:FairValueMeasurementsRecurringMemberus-gaap:MunicipalBondsMember2021-03-310000092122us-gaap:FairValueMeasurementsRecurringMemberus-gaap:FairValueInputsLevel1Memberus-gaap:FixedIncomeFundsMember2021-03-310000092122us-gaap:FairValueMeasurementsRecurringMemberus-gaap:FairValueInputsLevel2Memberus-gaap:FixedIncomeFundsMember2021-03-310000092122us-gaap:FairValueInputsLevel3Memberus-gaap:FairValueMeasurementsRecurringMemberus-gaap:FixedIncomeFundsMember2021-03-310000092122us-gaap:FairValueMeasurementsRecurringMemberus-gaap:FixedIncomeFundsMember2021-03-310000092122us-gaap:CorporateDebtSecuritiesMemberus-gaap:FairValueMeasurementsRecurringMemberus-gaap:FairValueInputsLevel1Member2021-03-310000092122us-gaap:CorporateDebtSecuritiesMemberus-gaap:FairValueMeasurementsRecurringMemberus-gaap:FairValueInputsLevel2Member2021-03-310000092122us-gaap:FairValueInputsLevel3Memberus-gaap:CorporateDebtSecuritiesMemberus-gaap:FairValueMeasurementsRecurringMember2021-03-310000092122us-gaap:CorporateDebtSecuritiesMemberus-gaap:FairValueMeasurementsRecurringMember2021-03-310000092122us-gaap:AssetBackedSecuritiesMemberus-gaap:FairValueMeasurementsRecurringMemberus-gaap:FairValueInputsLevel1Member2021-03-310000092122us-gaap:AssetBackedSecuritiesMemberus-gaap:FairValueMeasurementsRecurringMemberus-gaap:FairValueInputsLevel2Member2021-03-310000092122us-gaap:FairValueInputsLevel3Memberus-gaap:AssetBackedSecuritiesMemberus-gaap:FairValueMeasurementsRecurringMember2021-03-310000092122us-gaap:AssetBackedSecuritiesMemberus-gaap:FairValueMeasurementsRecurringMember2021-03-310000092122us-gaap:FairValueMeasurementsRecurringMemberus-gaap:FairValueInputsLevel1Memberus-gaap:PrivateEquityFundsMember2021-03-310000092122us-gaap:FairValueMeasurementsRecurringMemberus-gaap:FairValueInputsLevel2Memberus-gaap:PrivateEquityFundsMember2021-03-310000092122us-gaap:FairValueInputsLevel3Memberus-gaap:FairValueMeasurementsRecurringMemberus-gaap:PrivateEquityFundsMember2021-03-310000092122us-gaap:FairValueMeasurementsRecurringMemberus-gaap:FairValueMeasuredAtNetAssetValuePerShareMemberus-gaap:PrivateEquityFundsMember2021-03-310000092122us-gaap:FairValueMeasurementsRecurringMemberus-gaap:PrivateEquityFundsMember2021-03-310000092122us-gaap:FairValueMeasurementsRecurringMemberus-gaap:FairValueInputsLevel1Memberus-gaap:OtherThanSecuritiesInvestmentMember2021-03-310000092122us-gaap:FairValueMeasurementsRecurringMemberus-gaap:FairValueInputsLevel2Memberus-gaap:OtherThanSecuritiesInvestmentMember2021-03-310000092122us-gaap:FairValueInputsLevel3Memberus-gaap:FairValueMeasurementsRecurringMemberus-gaap:OtherThanSecuritiesInvestmentMember2021-03-310000092122us-gaap:FairValueMeasurementsRecurringMemberus-gaap:OtherThanSecuritiesInvestmentMember2021-03-310000092122us-gaap:FairValueMeasurementsRecurringMemberus-gaap:FairValueInputsLevel1Member2021-03-310000092122us-gaap:FairValueMeasurementsRecurringMemberus-gaap:FairValueInputsLevel2Member2021-03-310000092122us-gaap:FairValueInputsLevel3Memberus-gaap:FairValueMeasurementsRecurringMember2021-03-310000092122us-gaap:FairValueMeasurementsRecurringMember2021-03-310000092122us-gaap:FairValueMeasurementsRecurringMemberus-gaap:FairValueMeasuredAtNetAssetValuePerShareMember2021-03-310000092122us-gaap:FairValueMeasurementsRecurringMemberus-gaap:EnergyRelatedDerivativeMemberus-gaap:FairValueInputsLevel1Memberso:AlabamaPowerMember2021-03-310000092122us-gaap:FairValueMeasurementsRecurringMemberus-gaap:EnergyRelatedDerivativeMemberus-gaap:FairValueInputsLevel2Memberso:AlabamaPowerMember2021-03-310000092122us-gaap:FairValueInputsLevel3Memberus-gaap:FairValueMeasurementsRecurringMemberus-gaap:EnergyRelatedDerivativeMemberso:AlabamaPowerMember2021-03-310000092122us-gaap:FairValueMeasurementsRecurringMemberus-gaap:EnergyRelatedDerivativeMemberso:AlabamaPowerMember2021-03-310000092122us-gaap:FairValueMeasurementsRecurringMemberus-gaap:FairValueInputsLevel1Memberso:AlabamaPowerMemberso:DomesticEquityMember2021-03-310000092122us-gaap:FairValueMeasurementsRecurringMemberus-gaap:FairValueInputsLevel2Memberso:AlabamaPowerMemberso:DomesticEquityMember2021-03-310000092122us-gaap:FairValueInputsLevel3Memberus-gaap:FairValueMeasurementsRecurringMemberso:AlabamaPowerMemberso:DomesticEquityMember2021-03-310000092122us-gaap:FairValueMeasurementsRecurringMemberso:AlabamaPowerMemberso:DomesticEquityMember2021-03-310000092122us-gaap:FairValueMeasurementsRecurringMemberso:ForeignEquityMemberus-gaap:FairValueInputsLevel1Memberso:AlabamaPowerMember2021-03-310000092122us-gaap:FairValueMeasurementsRecurringMemberso:ForeignEquityMemberus-gaap:FairValueInputsLevel2Memberso:AlabamaPowerMember2021-03-310000092122us-gaap:FairValueInputsLevel3Memberus-gaap:FairValueMeasurementsRecurringMemberso:ForeignEquityMemberso:AlabamaPowerMember2021-03-310000092122us-gaap:FairValueMeasurementsRecurringMemberso:ForeignEquityMemberso:AlabamaPowerMember2021-03-310000092122us-gaap:FairValueMeasurementsRecurringMemberus-gaap:USTreasuryAndGovernmentMemberus-gaap:FairValueInputsLevel1Memberso:AlabamaPowerMember2021-03-310000092122us-gaap:FairValueMeasurementsRecurringMemberus-gaap:USTreasuryAndGovernmentMemberus-gaap:FairValueInputsLevel2Memberso:AlabamaPowerMember2021-03-310000092122us-gaap:FairValueInputsLevel3Memberus-gaap:FairValueMeasurementsRecurringMemberus-gaap:USTreasuryAndGovernmentMemberso:AlabamaPowerMember2021-03-310000092122us-gaap:FairValueMeasurementsRecurringMemberus-gaap:USTreasuryAndGovernmentMemberso:AlabamaPowerMember2021-03-310000092122us-gaap:FairValueMeasurementsRecurringMemberus-gaap:MunicipalBondsMemberus-gaap:FairValueInputsLevel1Memberso:AlabamaPowerMember2021-03-310000092122us-gaap:FairValueMeasurementsRecurringMemberus-gaap:MunicipalBondsMemberus-gaap:FairValueInputsLevel2Memberso:AlabamaPowerMember2021-03-310000092122us-gaap:FairValueInputsLevel3Memberus-gaap:FairValueMeasurementsRecurringMemberus-gaap:MunicipalBondsMemberso:AlabamaPowerMember2021-03-310000092122us-gaap:FairValueMeasurementsRecurringMemberus-gaap:MunicipalBondsMemberso:AlabamaPowerMember2021-03-310000092122us-gaap:CorporateDebtSecuritiesMemberus-gaap:FairValueMeasurementsRecurringMemberus-gaap:FairValueInputsLevel1Memberso:AlabamaPowerMember2021-03-310000092122us-gaap:CorporateDebtSecuritiesMemberus-gaap:FairValueMeasurementsRecurringMemberus-gaap:FairValueInputsLevel2Memberso:AlabamaPowerMember2021-03-310000092122us-gaap:FairValueInputsLevel3Memberus-gaap:CorporateDebtSecuritiesMemberus-gaap:FairValueMeasurementsRecurringMemberso:AlabamaPowerMember2021-03-310000092122us-gaap:CorporateDebtSecuritiesMemberus-gaap:FairValueMeasurementsRecurringMemberso:AlabamaPowerMember2021-03-310000092122us-gaap:AssetBackedSecuritiesMemberus-gaap:FairValueMeasurementsRecurringMemberus-gaap:FairValueInputsLevel1Memberso:AlabamaPowerMember2021-03-310000092122us-gaap:AssetBackedSecuritiesMemberus-gaap:FairValueMeasurementsRecurringMemberus-gaap:FairValueInputsLevel2Memberso:AlabamaPowerMember2021-03-310000092122us-gaap:FairValueInputsLevel3Memberus-gaap:AssetBackedSecuritiesMemberus-gaap:FairValueMeasurementsRecurringMemberso:AlabamaPowerMember2021-03-310000092122us-gaap:AssetBackedSecuritiesMemberus-gaap:FairValueMeasurementsRecurringMemberso:AlabamaPowerMember2021-03-310000092122us-gaap:FairValueMeasurementsRecurringMemberus-gaap:FairValueInputsLevel1Memberus-gaap:PrivateEquityFundsMemberso:AlabamaPowerMember2021-03-310000092122us-gaap:FairValueMeasurementsRecurringMemberus-gaap:FairValueInputsLevel2Memberus-gaap:PrivateEquityFundsMemberso:AlabamaPowerMember2021-03-310000092122us-gaap:FairValueInputsLevel3Memberus-gaap:FairValueMeasurementsRecurringMemberus-gaap:PrivateEquityFundsMemberso:AlabamaPowerMember2021-03-310000092122us-gaap:FairValueMeasurementsRecurringMemberus-gaap:FairValueMeasuredAtNetAssetValuePerShareMemberus-gaap:PrivateEquityFundsMemberso:AlabamaPowerMember2021-03-310000092122us-gaap:FairValueMeasurementsRecurringMemberus-gaap:PrivateEquityFundsMemberso:AlabamaPowerMember2021-03-310000092122us-gaap:FairValueMeasurementsRecurringMemberus-gaap:FairValueInputsLevel1Memberso:AlabamaPowerMemberus-gaap:OtherThanSecuritiesInvestmentMember2021-03-310000092122us-gaap:FairValueMeasurementsRecurringMemberus-gaap:FairValueInputsLevel2Memberso:AlabamaPowerMemberus-gaap:OtherThanSecuritiesInvestmentMember2021-03-310000092122us-gaap:FairValueInputsLevel3Memberus-gaap:FairValueMeasurementsRecurringMemberso:AlabamaPowerMemberus-gaap:OtherThanSecuritiesInvestmentMember2021-03-310000092122us-gaap:FairValueMeasurementsRecurringMemberso:AlabamaPowerMemberus-gaap:OtherThanSecuritiesInvestmentMember2021-03-310000092122us-gaap:FairValueMeasurementsRecurringMemberus-gaap:FairValueInputsLevel1Memberso:AlabamaPowerMember2021-03-310000092122us-gaap:FairValueMeasurementsRecurringMemberus-gaap:FairValueInputsLevel2Memberso:AlabamaPowerMember2021-03-310000092122us-gaap:FairValueInputsLevel3Memberus-gaap:FairValueMeasurementsRecurringMemberso:AlabamaPowerMember2021-03-310000092122us-gaap:FairValueMeasurementsRecurringMemberso:AlabamaPowerMember2021-03-310000092122us-gaap:FairValueMeasurementsRecurringMemberus-gaap:FairValueMeasuredAtNetAssetValuePerShareMemberso:AlabamaPowerMember2021-03-310000092122so:GeorgiaPowerMemberus-gaap:FairValueMeasurementsRecurringMemberus-gaap:EnergyRelatedDerivativeMemberus-gaap:FairValueInputsLevel1Member2021-03-310000092122so:GeorgiaPowerMemberus-gaap:FairValueMeasurementsRecurringMemberus-gaap:EnergyRelatedDerivativeMemberus-gaap:FairValueInputsLevel2Member2021-03-310000092122so:GeorgiaPowerMemberus-gaap:FairValueInputsLevel3Memberus-gaap:FairValueMeasurementsRecurringMemberus-gaap:EnergyRelatedDerivativeMember2021-03-310000092122so:GeorgiaPowerMemberus-gaap:FairValueMeasurementsRecurringMemberus-gaap:EnergyRelatedDerivativeMember2021-03-310000092122so:GeorgiaPowerMemberus-gaap:FairValueMeasurementsRecurringMemberus-gaap:FairValueInputsLevel1Memberso:DomesticEquityMember2021-03-310000092122so:GeorgiaPowerMemberus-gaap:FairValueMeasurementsRecurringMemberus-gaap:FairValueInputsLevel2Memberso:DomesticEquityMember2021-03-310000092122so:GeorgiaPowerMemberus-gaap:FairValueInputsLevel3Memberus-gaap:FairValueMeasurementsRecurringMemberso:DomesticEquityMember2021-03-310000092122so:GeorgiaPowerMemberus-gaap:FairValueMeasurementsRecurringMemberso:DomesticEquityMember2021-03-310000092122so:GeorgiaPowerMemberus-gaap:FairValueMeasurementsRecurringMemberso:ForeignEquityMemberus-gaap:FairValueInputsLevel1Member2021-03-310000092122so:GeorgiaPowerMemberus-gaap:FairValueMeasurementsRecurringMemberso:ForeignEquityMemberus-gaap:FairValueInputsLevel2Member2021-03-310000092122so:GeorgiaPowerMemberus-gaap:FairValueInputsLevel3Memberus-gaap:FairValueMeasurementsRecurringMemberso:ForeignEquityMember2021-03-310000092122so:GeorgiaPowerMemberus-gaap:FairValueMeasurementsRecurringMemberso:ForeignEquityMember2021-03-310000092122so:GeorgiaPowerMemberus-gaap:FairValueMeasurementsRecurringMemberus-gaap:USTreasuryAndGovernmentMemberus-gaap:FairValueInputsLevel1Member2021-03-310000092122so:GeorgiaPowerMemberus-gaap:FairValueMeasurementsRecurringMemberus-gaap:USTreasuryAndGovernmentMemberus-gaap:FairValueInputsLevel2Member2021-03-310000092122so:GeorgiaPowerMemberus-gaap:FairValueInputsLevel3Memberus-gaap:FairValueMeasurementsRecurringMemberus-gaap:USTreasuryAndGovernmentMember2021-03-310000092122so:GeorgiaPowerMemberus-gaap:FairValueMeasurementsRecurringMemberus-gaap:USTreasuryAndGovernmentMember2021-03-310000092122so:GeorgiaPowerMemberus-gaap:FairValueMeasurementsRecurringMemberus-gaap:MunicipalBondsMemberus-gaap:FairValueInputsLevel1Member2021-03-310000092122so:GeorgiaPowerMemberus-gaap:FairValueMeasurementsRecurringMemberus-gaap:MunicipalBondsMemberus-gaap:FairValueInputsLevel2Member2021-03-310000092122so:GeorgiaPowerMemberus-gaap:FairValueInputsLevel3Memberus-gaap:FairValueMeasurementsRecurringMemberus-gaap:MunicipalBondsMember2021-03-310000092122so:GeorgiaPowerMemberus-gaap:FairValueMeasurementsRecurringMemberus-gaap:MunicipalBondsMember2021-03-310000092122so:GeorgiaPowerMemberus-gaap:CorporateDebtSecuritiesMemberus-gaap:FairValueMeasurementsRecurringMemberus-gaap:FairValueInputsLevel1Member2021-03-310000092122so:GeorgiaPowerMemberus-gaap:CorporateDebtSecuritiesMemberus-gaap:FairValueMeasurementsRecurringMemberus-gaap:FairValueInputsLevel2Member2021-03-310000092122so:GeorgiaPowerMemberus-gaap:FairValueInputsLevel3Memberus-gaap:CorporateDebtSecuritiesMemberus-gaap:FairValueMeasurementsRecurringMember2021-03-310000092122so:GeorgiaPowerMemberus-gaap:CorporateDebtSecuritiesMemberus-gaap:FairValueMeasurementsRecurringMember2021-03-310000092122so:GeorgiaPowerMemberus-gaap:AssetBackedSecuritiesMemberus-gaap:FairValueMeasurementsRecurringMemberus-gaap:FairValueInputsLevel1Member2021-03-310000092122so:GeorgiaPowerMemberus-gaap:AssetBackedSecuritiesMemberus-gaap:FairValueMeasurementsRecurringMemberus-gaap:FairValueInputsLevel2Member2021-03-310000092122so:GeorgiaPowerMemberus-gaap:FairValueInputsLevel3Memberus-gaap:AssetBackedSecuritiesMemberus-gaap:FairValueMeasurementsRecurringMember2021-03-310000092122so:GeorgiaPowerMemberus-gaap:AssetBackedSecuritiesMemberus-gaap:FairValueMeasurementsRecurringMember2021-03-310000092122so:GeorgiaPowerMemberus-gaap:FairValueMeasurementsRecurringMemberus-gaap:FairValueInputsLevel1Memberus-gaap:OtherThanSecuritiesInvestmentMember2021-03-310000092122so:GeorgiaPowerMemberus-gaap:FairValueMeasurementsRecurringMemberus-gaap:FairValueInputsLevel2Memberus-gaap:OtherThanSecuritiesInvestmentMember2021-03-310000092122so:GeorgiaPowerMemberus-gaap:FairValueInputsLevel3Memberus-gaap:FairValueMeasurementsRecurringMemberus-gaap:OtherThanSecuritiesInvestmentMember2021-03-310000092122so:GeorgiaPowerMemberus-gaap:FairValueMeasurementsRecurringMemberus-gaap:OtherThanSecuritiesInvestmentMember2021-03-310000092122so:GeorgiaPowerMemberus-gaap:FairValueMeasurementsRecurringMemberus-gaap:FairValueInputsLevel1Member2021-03-310000092122so:GeorgiaPowerMemberus-gaap:FairValueMeasurementsRecurringMemberus-gaap:FairValueInputsLevel2Member2021-03-310000092122so:GeorgiaPowerMemberus-gaap:FairValueInputsLevel3Memberus-gaap:FairValueMeasurementsRecurringMember2021-03-310000092122so:GeorgiaPowerMemberus-gaap:FairValueMeasurementsRecurringMember2021-03-310000092122so:MississippiPowerMemberus-gaap:FairValueMeasurementsRecurringMemberus-gaap:EnergyRelatedDerivativeMemberus-gaap:FairValueInputsLevel1Member2021-03-310000092122so:MississippiPowerMemberus-gaap:FairValueMeasurementsRecurringMemberus-gaap:EnergyRelatedDerivativeMemberus-gaap:FairValueInputsLevel2Member2021-03-310000092122so:MississippiPowerMemberus-gaap:FairValueInputsLevel3Memberus-gaap:FairValueMeasurementsRecurringMemberus-gaap:EnergyRelatedDerivativeMember2021-03-310000092122so:MississippiPowerMemberus-gaap:FairValueMeasurementsRecurringMemberus-gaap:EnergyRelatedDerivativeMember2021-03-310000092122us-gaap:FairValueMeasurementsRecurringMemberus-gaap:EnergyRelatedDerivativeMemberso:SouthernPowerMemberus-gaap:FairValueInputsLevel1Member2021-03-310000092122us-gaap:FairValueMeasurementsRecurringMemberus-gaap:EnergyRelatedDerivativeMemberso:SouthernPowerMemberus-gaap:FairValueInputsLevel2Member2021-03-310000092122us-gaap:FairValueInputsLevel3Memberus-gaap:FairValueMeasurementsRecurringMemberus-gaap:EnergyRelatedDerivativeMemberso:SouthernPowerMember2021-03-310000092122us-gaap:FairValueMeasurementsRecurringMemberus-gaap:EnergyRelatedDerivativeMemberso:SouthernPowerMember2021-03-310000092122us-gaap:FairValueMeasurementsRecurringMemberso:SouthernPowerMemberus-gaap:FairValueInputsLevel1Memberus-gaap:ForeignExchangeContractMember2021-03-310000092122us-gaap:FairValueMeasurementsRecurringMemberso:SouthernPowerMemberus-gaap:FairValueInputsLevel2Memberus-gaap:ForeignExchangeContractMember2021-03-310000092122us-gaap:FairValueInputsLevel3Memberus-gaap:FairValueMeasurementsRecurringMemberso:SouthernPowerMemberus-gaap:ForeignExchangeContractMember2021-03-310000092122us-gaap:FairValueMeasurementsRecurringMemberso:SouthernPowerMemberus-gaap:ForeignExchangeContractMember2021-03-310000092122us-gaap:FairValueMeasurementsRecurringMemberso:SouthernPowerMemberus-gaap:FairValueInputsLevel1Member2021-03-310000092122us-gaap:FairValueMeasurementsRecurringMemberso:SouthernPowerMemberus-gaap:FairValueInputsLevel2Member2021-03-310000092122us-gaap:FairValueInputsLevel3Memberus-gaap:FairValueMeasurementsRecurringMemberso:SouthernPowerMember2021-03-310000092122us-gaap:FairValueMeasurementsRecurringMemberso:SouthernPowerMember2021-03-310000092122us-gaap:FairValueMeasurementsRecurringMemberus-gaap:EnergyRelatedDerivativeMemberus-gaap:FairValueInputsLevel1Memberso:SouthernCompanyGasMember2021-03-310000092122us-gaap:FairValueMeasurementsRecurringMemberus-gaap:EnergyRelatedDerivativeMemberus-gaap:FairValueInputsLevel2Memberso:SouthernCompanyGasMember2021-03-310000092122us-gaap:FairValueInputsLevel3Memberus-gaap:FairValueMeasurementsRecurringMemberus-gaap:EnergyRelatedDerivativeMemberso:SouthernCompanyGasMember2021-03-310000092122us-gaap:FairValueMeasurementsRecurringMemberus-gaap:EnergyRelatedDerivativeMemberso:SouthernCompanyGasMember2021-03-310000092122us-gaap:FairValueMeasurementsRecurringMemberus-gaap:FairValueInputsLevel1Memberso:SouthernCompanyGasMemberso:DomesticEquityMember2021-03-310000092122us-gaap:FairValueMeasurementsRecurringMemberus-gaap:FairValueInputsLevel2Memberso:SouthernCompanyGasMemberso:DomesticEquityMember2021-03-310000092122us-gaap:FairValueInputsLevel3Memberus-gaap:FairValueMeasurementsRecurringMemberso:SouthernCompanyGasMemberso:DomesticEquityMember2021-03-310000092122us-gaap:FairValueMeasurementsRecurringMemberso:SouthernCompanyGasMemberso:DomesticEquityMember2021-03-310000092122us-gaap:FairValueMeasurementsRecurringMemberso:ForeignEquityMemberus-gaap:FairValueInputsLevel1Memberso:SouthernCompanyGasMember2021-03-310000092122us-gaap:FairValueMeasurementsRecurringMemberso:ForeignEquityMemberus-gaap:FairValueInputsLevel2Memberso:SouthernCompanyGasMember2021-03-310000092122us-gaap:FairValueInputsLevel3Memberus-gaap:FairValueMeasurementsRecurringMemberso:ForeignEquityMemberso:SouthernCompanyGasMember2021-03-310000092122us-gaap:FairValueMeasurementsRecurringMemberso:ForeignEquityMemberso:SouthernCompanyGasMember2021-03-310000092122us-gaap:FairValueMeasurementsRecurringMemberus-gaap:FairValueInputsLevel1Memberus-gaap:FixedIncomeFundsMemberso:SouthernCompanyGasMember2021-03-310000092122us-gaap:FairValueMeasurementsRecurringMemberus-gaap:FairValueInputsLevel2Memberus-gaap:FixedIncomeFundsMemberso:SouthernCompanyGasMember2021-03-310000092122us-gaap:FairValueInputsLevel3Memberus-gaap:FairValueMeasurementsRecurringMemberus-gaap:FixedIncomeFundsMemberso:SouthernCompanyGasMember2021-03-310000092122us-gaap:FairValueMeasurementsRecurringMemberus-gaap:FixedIncomeFundsMemberso:SouthernCompanyGasMember2021-03-310000092122us-gaap:FairValueMeasurementsRecurringMemberus-gaap:FairValueInputsLevel1Memberso:SouthernCompanyGasMember2021-03-310000092122us-gaap:FairValueMeasurementsRecurringMemberus-gaap:FairValueInputsLevel2Memberso:SouthernCompanyGasMember2021-03-310000092122us-gaap:FairValueInputsLevel3Memberus-gaap:FairValueMeasurementsRecurringMemberso:SouthernCompanyGasMember2021-03-310000092122us-gaap:FairValueMeasurementsRecurringMemberso:SouthernCompanyGasMember2021-03-310000092122us-gaap:PrivateEquityFundsMemberso:AlabamaPowerMember2021-03-310000092122us-gaap:FairValueInputsLevel3Memberus-gaap:EnergyRelatedDerivativeMemberso:SouthernCompanyGasMember2021-03-31iso4217:USDutr:MMBTU0000092122srt:MinimumMemberus-gaap:MeasurementInputCommodityForwardPriceMemberus-gaap:FairValueInputsLevel3Memberus-gaap:MarketApproachValuationTechniqueMemberus-gaap:EnergyRelatedDerivativeMemberso:SouthernCompanyGasMember2021-03-310000092122us-gaap:MeasurementInputCommodityForwardPriceMemberus-gaap:FairValueInputsLevel3Memberus-gaap:MarketApproachValuationTechniqueMemberus-gaap:EnergyRelatedDerivativeMembersrt:MaximumMemberso:SouthernCompanyGasMember2021-03-31utr:MMBTU0000092122us-gaap:PublicUtilitiesInventoryNaturalGasMember2021-03-310000092122us-gaap:PublicUtilitiesInventoryNaturalGasMemberso:AlabamaPowerMember2021-03-310000092122so:GeorgiaPowerMemberus-gaap:PublicUtilitiesInventoryNaturalGasMember2021-03-310000092122so:MississippiPowerMemberus-gaap:PublicUtilitiesInventoryNaturalGasMember2021-03-310000092122so:SouthernPowerMemberus-gaap:PublicUtilitiesInventoryNaturalGasMember2021-03-310000092122us-gaap:PublicUtilitiesInventoryNaturalGasMemberso:SouthernCompanyGasMember2021-03-310000092122us-gaap:NondesignatedMemberus-gaap:LongMemberus-gaap:PublicUtilitiesInventoryNaturalGasMemberso:SouthernCompanyGasMember2021-03-310000092122us-gaap:NondesignatedMemberus-gaap:ShortMemberus-gaap:PublicUtilitiesInventoryNaturalGasMemberso:SouthernCompanyGasMember2021-03-310000092122so:CashFlowHedgesOfExistingDebtMemberso:MississippiPowerMemberus-gaap:InterestRateContractMember2021-03-310000092122so:CashFlowHedgesOfExistingDebtMemberso:MississippiPowerMemberus-gaap:InterestRateContractMember2021-01-012021-03-310000092122us-gaap:InterestRateContractMemberso:SouthernCompanyMemberso:FairValueHedgesOfExistingDebtMember2021-03-310000092122us-gaap:InterestRateContractMemberso:SouthernCompanyMemberso:FairValueHedgesOfExistingDebtMember2021-01-012021-03-310000092122us-gaap:InterestRateContractMemberso:SouthernCompanyMemberso:FairValueHedgesOfExistingDebtMemberus-gaap:LondonInterbankOfferedRateLIBORMember2021-01-012021-03-310000092122us-gaap:InterestRateContractMember2021-03-310000092122so:CashFlowHedgesOfExistingDebtMemberus-gaap:ForeignExchangeContractMemberso:SouthernPowerMemberso:HedgingMaturityDateOneMember2021-03-310000092122so:CashFlowHedgesOfExistingDebtMemberus-gaap:ForeignExchangeContractMemberso:SouthernPowerMemberso:HedgingMaturityDateOneMember2021-01-012021-03-31iso4217:EUR0000092122so:CashFlowHedgesOfExistingDebtMemberus-gaap:ForeignExchangeContractMemberso:SouthernPowerMemberso:HedgingMaturityDateTwoMember2021-03-310000092122so:CashFlowHedgesOfExistingDebtMemberus-gaap:ForeignExchangeContractMemberso:SouthernPowerMemberso:HedgingMaturityDateTwoMember2021-01-012021-03-310000092122so:CashFlowHedgesOfExistingDebtMemberus-gaap:ForeignExchangeContractMember2021-03-310000092122so:ParentCompanyandSouthernPowerMember2021-03-310000092122us-gaap:DesignatedAsHedgingInstrumentMemberus-gaap:EnergyRelatedDerivativeMemberso:AssetsFromRiskManagementActivitiesMemberso:HedgingInstrumentsForRegulatoryPurposesMember2021-03-310000092122us-gaap:OtherCurrentLiabilitiesMemberus-gaap:DesignatedAsHedgingInstrumentMemberus-gaap:EnergyRelatedDerivativeMemberso:HedgingInstrumentsForRegulatoryPurposesMember2021-03-310000092122us-gaap:DesignatedAsHedgingInstrumentMemberus-gaap:EnergyRelatedDerivativeMemberso:AssetsFromRiskManagementActivitiesMemberso:HedgingInstrumentsForRegulatoryPurposesMember2020-12-310000092122us-gaap:OtherCurrentLiabilitiesMemberus-gaap:DesignatedAsHedgingInstrumentMemberus-gaap:EnergyRelatedDerivativeMemberso:HedgingInstrumentsForRegulatoryPurposesMember2020-12-310000092122us-gaap:DesignatedAsHedgingInstrumentMemberus-gaap:EnergyRelatedDerivativeMemberso:OtherDeferredChargesAndAssetsMemberso:HedgingInstrumentsForRegulatoryPurposesMember2021-03-310000092122us-gaap:DesignatedAsHedgingInstrumentMemberus-gaap:EnergyRelatedDerivativeMemberso:OtherDeferredCreditsAndLiabilitiesMemberso:HedgingInstrumentsForRegulatoryPurposesMember2021-03-310000092122us-gaap:DesignatedAsHedgingInstrumentMemberus-gaap:EnergyRelatedDerivativeMemberso:OtherDeferredChargesAndAssetsMemberso:HedgingInstrumentsForRegulatoryPurposesMember2020-12-310000092122us-gaap:DesignatedAsHedgingInstrumentMemberus-gaap:EnergyRelatedDerivativeMemberso:OtherDeferredCreditsAndLiabilitiesMemberso:HedgingInstrumentsForRegulatoryPurposesMember2020-12-310000092122us-gaap:DesignatedAsHedgingInstrumentMemberso:HedgingInstrumentsForRegulatoryPurposesMember2021-03-310000092122us-gaap:DesignatedAsHedgingInstrumentMemberso:HedgingInstrumentsForRegulatoryPurposesMember2020-12-310000092122us-gaap:DesignatedAsHedgingInstrumentMemberus-gaap:EnergyRelatedDerivativeMemberso:CashFlowAndFairValueHedgingMemberso:AssetsFromRiskManagementActivitiesMember2021-03-310000092122us-gaap:OtherCurrentLiabilitiesMemberus-gaap:DesignatedAsHedgingInstrumentMemberus-gaap:EnergyRelatedDerivativeMemberso:CashFlowAndFairValueHedgingMember2021-03-310000092122us-gaap:DesignatedAsHedgingInstrumentMemberus-gaap:EnergyRelatedDerivativeMemberso:CashFlowAndFairValueHedgingMemberso:AssetsFromRiskManagementActivitiesMember2020-12-310000092122us-gaap:OtherCurrentLiabilitiesMemberus-gaap:DesignatedAsHedgingInstrumentMemberus-gaap:EnergyRelatedDerivativeMemberso:CashFlowAndFairValueHedgingMember2020-12-310000092122us-gaap:InterestRateContractMemberus-gaap:DesignatedAsHedgingInstrumentMemberso:CashFlowAndFairValueHedgingMemberso:AssetsFromRiskManagementActivitiesMember2021-03-310000092122us-gaap:OtherCurrentLiabilitiesMemberus-gaap:InterestRateContractMemberus-gaap:DesignatedAsHedgingInstrumentMemberso:CashFlowAndFairValueHedgingMember2021-03-310000092122us-gaap:InterestRateContractMemberus-gaap:DesignatedAsHedgingInstrumentMemberso:CashFlowAndFairValueHedgingMemberso:AssetsFromRiskManagementActivitiesMember2020-12-310000092122us-gaap:OtherCurrentLiabilitiesMemberus-gaap:InterestRateContractMemberus-gaap:DesignatedAsHedgingInstrumentMemberso:CashFlowAndFairValueHedgingMember2020-12-310000092122us-gaap:ForeignExchangeContractMemberus-gaap:DesignatedAsHedgingInstrumentMemberso:CashFlowAndFairValueHedgingMemberso:AssetsFromRiskManagementActivitiesMember2021-03-310000092122us-gaap:ForeignExchangeContractMemberus-gaap:OtherCurrentLiabilitiesMemberus-gaap:DesignatedAsHedgingInstrumentMemberso:CashFlowAndFairValueHedgingMember2021-03-310000092122us-gaap:ForeignExchangeContractMemberus-gaap:DesignatedAsHedgingInstrumentMemberso:CashFlowAndFairValueHedgingMemberso:AssetsFromRiskManagementActivitiesMember2020-12-310000092122us-gaap:ForeignExchangeContractMemberus-gaap:OtherCurrentLiabilitiesMemberus-gaap:DesignatedAsHedgingInstrumentMemberso:CashFlowAndFairValueHedgingMember2020-12-310000092122us-gaap:ForeignExchangeContractMemberus-gaap:DesignatedAsHedgingInstrumentMemberso:CashFlowAndFairValueHedgingMemberso:OtherDeferredChargesAndAssetsMember2021-03-310000092122us-gaap:ForeignExchangeContractMemberus-gaap:DesignatedAsHedgingInstrumentMemberso:CashFlowAndFairValueHedgingMemberso:OtherDeferredCreditsAndLiabilitiesMember2021-03-310000092122us-gaap:ForeignExchangeContractMemberus-gaap:DesignatedAsHedgingInstrumentMemberso:CashFlowAndFairValueHedgingMemberso:OtherDeferredChargesAndAssetsMember2020-12-310000092122us-gaap:ForeignExchangeContractMemberus-gaap:DesignatedAsHedgingInstrumentMemberso:CashFlowAndFairValueHedgingMemberso:OtherDeferredCreditsAndLiabilitiesMember2020-12-310000092122us-gaap:DesignatedAsHedgingInstrumentMemberso:CashFlowAndFairValueHedgingMember2021-03-310000092122us-gaap:DesignatedAsHedgingInstrumentMemberso:CashFlowAndFairValueHedgingMember2020-12-310000092122us-gaap:NondesignatedMemberus-gaap:EnergyRelatedDerivativeMemberso:AssetsFromRiskManagementActivitiesMember2021-03-310000092122us-gaap:OtherCurrentLiabilitiesMemberus-gaap:NondesignatedMemberus-gaap:EnergyRelatedDerivativeMember2021-03-310000092122us-gaap:NondesignatedMemberus-gaap:EnergyRelatedDerivativeMemberso:AssetsFromRiskManagementActivitiesMember2020-12-310000092122us-gaap:OtherCurrentLiabilitiesMemberus-gaap:NondesignatedMemberus-gaap:EnergyRelatedDerivativeMember2020-12-310000092122us-gaap:NondesignatedMemberus-gaap:EnergyRelatedDerivativeMemberso:OtherDeferredChargesAndAssetsMember2021-03-310000092122us-gaap:NondesignatedMemberus-gaap:EnergyRelatedDerivativeMemberso:OtherDeferredCreditsAndLiabilitiesMember2021-03-310000092122us-gaap:NondesignatedMemberus-gaap:EnergyRelatedDerivativeMemberso:OtherDeferredChargesAndAssetsMember2020-12-310000092122us-gaap:NondesignatedMemberus-gaap:EnergyRelatedDerivativeMemberso:OtherDeferredCreditsAndLiabilitiesMember2020-12-310000092122us-gaap:NondesignatedMember2021-03-310000092122us-gaap:NondesignatedMember2020-12-310000092122us-gaap:OtherCurrentAssetsMemberus-gaap:DesignatedAsHedgingInstrumentMemberus-gaap:EnergyRelatedDerivativeMemberso:AlabamaPowerMemberso:HedgingInstrumentsForRegulatoryPurposesMember2021-03-310000092122us-gaap:OtherCurrentLiabilitiesMemberus-gaap:DesignatedAsHedgingInstrumentMemberus-gaap:EnergyRelatedDerivativeMemberso:AlabamaPowerMemberso:HedgingInstrumentsForRegulatoryPurposesMember2021-03-310000092122us-gaap:OtherCurrentAssetsMemberus-gaap:DesignatedAsHedgingInstrumentMemberus-gaap:EnergyRelatedDerivativeMemberso:AlabamaPowerMemberso:HedgingInstrumentsForRegulatoryPurposesMember2020-12-310000092122us-gaap:OtherCurrentLiabilitiesMemberus-gaap:DesignatedAsHedgingInstrumentMemberus-gaap:EnergyRelatedDerivativeMemberso:AlabamaPowerMemberso:HedgingInstrumentsForRegulatoryPurposesMember2020-12-310000092122us-gaap:DesignatedAsHedgingInstrumentMemberus-gaap:EnergyRelatedDerivativeMemberso:OtherDeferredChargesAndAssetsMemberso:AlabamaPowerMemberso:HedgingInstrumentsForRegulatoryPurposesMember2021-03-310000092122us-gaap:DesignatedAsHedgingInstrumentMemberus-gaap:EnergyRelatedDerivativeMemberso:OtherDeferredCreditsAndLiabilitiesMemberso:AlabamaPowerMemberso:HedgingInstrumentsForRegulatoryPurposesMember2021-03-310000092122us-gaap:DesignatedAsHedgingInstrumentMemberus-gaap:EnergyRelatedDerivativeMemberso:OtherDeferredChargesAndAssetsMemberso:AlabamaPowerMemberso:HedgingInstrumentsForRegulatoryPurposesMember2020-12-310000092122us-gaap:DesignatedAsHedgingInstrumentMemberus-gaap:EnergyRelatedDerivativeMemberso:OtherDeferredCreditsAndLiabilitiesMemberso:AlabamaPowerMemberso:HedgingInstrumentsForRegulatoryPurposesMember2020-12-310000092122us-gaap:DesignatedAsHedgingInstrumentMemberso:AlabamaPowerMemberso:HedgingInstrumentsForRegulatoryPurposesMember2021-03-310000092122us-gaap:DesignatedAsHedgingInstrumentMemberso:AlabamaPowerMemberso:HedgingInstrumentsForRegulatoryPurposesMember2020-12-310000092122us-gaap:OtherCurrentAssetsMemberso:GeorgiaPowerMemberus-gaap:DesignatedAsHedgingInstrumentMemberus-gaap:EnergyRelatedDerivativeMemberso:HedgingInstrumentsForRegulatoryPurposesMember2021-03-310000092122so:GeorgiaPowerMemberus-gaap:OtherCurrentLiabilitiesMemberus-gaap:DesignatedAsHedgingInstrumentMemberus-gaap:EnergyRelatedDerivativeMemberso:HedgingInstrumentsForRegulatoryPurposesMember2021-03-310000092122us-gaap:OtherCurrentAssetsMemberso:GeorgiaPowerMemberus-gaap:DesignatedAsHedgingInstrumentMemberus-gaap:EnergyRelatedDerivativeMemberso:HedgingInstrumentsForRegulatoryPurposesMember2020-12-310000092122so:GeorgiaPowerMemberus-gaap:OtherCurrentLiabilitiesMemberus-gaap:DesignatedAsHedgingInstrumentMemberus-gaap:EnergyRelatedDerivativeMemberso:HedgingInstrumentsForRegulatoryPurposesMember2020-12-310000092122so:GeorgiaPowerMemberus-gaap:DesignatedAsHedgingInstrumentMemberus-gaap:EnergyRelatedDerivativeMemberso:OtherDeferredChargesAndAssetsMemberso:HedgingInstrumentsForRegulatoryPurposesMember2021-03-310000092122so:GeorgiaPowerMemberus-gaap:DesignatedAsHedgingInstrumentMemberus-gaap:EnergyRelatedDerivativeMemberso:OtherDeferredCreditsAndLiabilitiesMemberso:HedgingInstrumentsForRegulatoryPurposesMember2021-03-310000092122so:GeorgiaPowerMemberus-gaap:DesignatedAsHedgingInstrumentMemberus-gaap:EnergyRelatedDerivativeMemberso:OtherDeferredChargesAndAssetsMemberso:HedgingInstrumentsForRegulatoryPurposesMember2020-12-310000092122so:GeorgiaPowerMemberus-gaap:DesignatedAsHedgingInstrumentMemberus-gaap:EnergyRelatedDerivativeMemberso:OtherDeferredCreditsAndLiabilitiesMemberso:HedgingInstrumentsForRegulatoryPurposesMember2020-12-310000092122so:GeorgiaPowerMemberus-gaap:DesignatedAsHedgingInstrumentMemberso:HedgingInstrumentsForRegulatoryPurposesMember2021-03-310000092122so:GeorgiaPowerMemberus-gaap:DesignatedAsHedgingInstrumentMemberso:HedgingInstrumentsForRegulatoryPurposesMember2020-12-310000092122us-gaap:OtherCurrentAssetsMemberso:MississippiPowerMemberus-gaap:DesignatedAsHedgingInstrumentMemberus-gaap:EnergyRelatedDerivativeMemberso:HedgingInstrumentsForRegulatoryPurposesMember2021-03-310000092122us-gaap:OtherCurrentLiabilitiesMemberso:MississippiPowerMemberus-gaap:DesignatedAsHedgingInstrumentMemberus-gaap:EnergyRelatedDerivativeMemberso:HedgingInstrumentsForRegulatoryPurposesMember2021-03-310000092122us-gaap:OtherCurrentAssetsMemberso:MississippiPowerMemberus-gaap:DesignatedAsHedgingInstrumentMemberus-gaap:EnergyRelatedDerivativeMemberso:HedgingInstrumentsForRegulatoryPurposesMember2020-12-310000092122us-gaap:OtherCurrentLiabilitiesMemberso:MississippiPowerMemberus-gaap:DesignatedAsHedgingInstrumentMemberus-gaap:EnergyRelatedDerivativeMemberso:HedgingInstrumentsForRegulatoryPurposesMember2020-12-310000092122so:MississippiPowerMemberus-gaap:DesignatedAsHedgingInstrumentMemberus-gaap:EnergyRelatedDerivativeMemberso:OtherDeferredChargesAndAssetsMemberso:HedgingInstrumentsForRegulatoryPurposesMember2021-03-310000092122so:MississippiPowerMemberus-gaap:DesignatedAsHedgingInstrumentMemberus-gaap:EnergyRelatedDerivativeMemberso:OtherDeferredCreditsAndLiabilitiesMemberso:HedgingInstrumentsForRegulatoryPurposesMember2021-03-310000092122so:MississippiPowerMemberus-gaap:DesignatedAsHedgingInstrumentMemberus-gaap:EnergyRelatedDerivativeMemberso:OtherDeferredChargesAndAssetsMemberso:HedgingInstrumentsForRegulatoryPurposesMember2020-12-310000092122so:MississippiPowerMemberus-gaap:DesignatedAsHedgingInstrumentMemberus-gaap:EnergyRelatedDerivativeMemberso:OtherDeferredCreditsAndLiabilitiesMemberso:HedgingInstrumentsForRegulatoryPurposesMember2020-12-310000092122so:MississippiPowerMemberus-gaap:DesignatedAsHedgingInstrumentMemberso:HedgingInstrumentsForRegulatoryPurposesMember2021-03-310000092122so:MississippiPowerMemberus-gaap:DesignatedAsHedgingInstrumentMemberso:HedgingInstrumentsForRegulatoryPurposesMember2020-12-310000092122us-gaap:OtherCurrentAssetsMemberus-gaap:DesignatedAsHedgingInstrumentMemberus-gaap:EnergyRelatedDerivativeMemberso:CashFlowAndFairValueHedgingMemberso:SouthernPowerMember2021-03-310000092122us-gaap:OtherCurrentLiabilitiesMemberus-gaap:DesignatedAsHedgingInstrumentMemberus-gaap:EnergyRelatedDerivativeMemberso:CashFlowAndFairValueHedgingMemberso:SouthernPowerMember2021-03-310000092122us-gaap:OtherCurrentAssetsMemberus-gaap:DesignatedAsHedgingInstrumentMemberus-gaap:EnergyRelatedDerivativeMemberso:CashFlowAndFairValueHedgingMemberso:SouthernPowerMember2020-12-310000092122us-gaap:OtherCurrentLiabilitiesMemberus-gaap:DesignatedAsHedgingInstrumentMemberus-gaap:EnergyRelatedDerivativeMemberso:CashFlowAndFairValueHedgingMemberso:SouthernPowerMember2020-12-310000092122us-gaap:OtherCurrentAssetsMemberus-gaap:ForeignExchangeContractMemberus-gaap:DesignatedAsHedgingInstrumentMemberso:CashFlowAndFairValueHedgingMemberso:SouthernPowerMember2021-03-310000092122us-gaap:ForeignExchangeContractMemberus-gaap:OtherCurrentLiabilitiesMemberus-gaap:DesignatedAsHedgingInstrumentMemberso:CashFlowAndFairValueHedgingMemberso:SouthernPowerMember2021-03-310000092122us-gaap:OtherCurrentAssetsMemberus-gaap:ForeignExchangeContractMemberus-gaap:DesignatedAsHedgingInstrumentMemberso:CashFlowAndFairValueHedgingMemberso:SouthernPowerMember2020-12-310000092122us-gaap:ForeignExchangeContractMemberus-gaap:OtherCurrentLiabilitiesMemberus-gaap:DesignatedAsHedgingInstrumentMemberso:CashFlowAndFairValueHedgingMemberso:SouthernPowerMember2020-12-310000092122us-gaap:ForeignExchangeContractMemberus-gaap:DesignatedAsHedgingInstrumentMemberso:CashFlowAndFairValueHedgingMemberso:SouthernPowerMemberso:OtherDeferredChargesAndAssetsMember2021-03-310000092122us-gaap:ForeignExchangeContractMemberus-gaap:DesignatedAsHedgingInstrumentMemberso:CashFlowAndFairValueHedgingMemberso:SouthernPowerMemberso:OtherDeferredCreditsAndLiabilitiesMember2021-03-310000092122us-gaap:ForeignExchangeContractMemberus-gaap:DesignatedAsHedgingInstrumentMemberso:CashFlowAndFairValueHedgingMemberso:SouthernPowerMemberso:OtherDeferredChargesAndAssetsMember2020-12-310000092122us-gaap:ForeignExchangeContractMemberus-gaap:DesignatedAsHedgingInstrumentMemberso:CashFlowAndFairValueHedgingMemberso:SouthernPowerMemberso:OtherDeferredCreditsAndLiabilitiesMember2020-12-310000092122us-gaap:DesignatedAsHedgingInstrumentMemberso:CashFlowAndFairValueHedgingMemberso:SouthernPowerMember2021-03-310000092122us-gaap:DesignatedAsHedgingInstrumentMemberso:CashFlowAndFairValueHedgingMemberso:SouthernPowerMember2020-12-310000092122us-gaap:OtherCurrentAssetsMemberus-gaap:NondesignatedMemberus-gaap:EnergyRelatedDerivativeMemberso:SouthernPowerMember2021-03-310000092122us-gaap:OtherCurrentLiabilitiesMemberus-gaap:NondesignatedMemberus-gaap:EnergyRelatedDerivativeMemberso:SouthernPowerMember2021-03-310000092122us-gaap:OtherCurrentAssetsMemberus-gaap:NondesignatedMemberus-gaap:EnergyRelatedDerivativeMemberso:SouthernPowerMember2020-12-310000092122us-gaap:OtherCurrentLiabilitiesMemberus-gaap:NondesignatedMemberus-gaap:EnergyRelatedDerivativeMemberso:SouthernPowerMember2020-12-310000092122us-gaap:NondesignatedMemberso:SouthernPowerMember2021-03-310000092122us-gaap:NondesignatedMemberso:SouthernPowerMember2020-12-310000092122us-gaap:DesignatedAsHedgingInstrumentMemberus-gaap:EnergyRelatedDerivativeMemberso:AssetsFromRiskManagementActivitiesMemberso:HedgingInstrumentsForRegulatoryPurposesMemberso:SouthernCompanyGasMember2021-03-310000092122us-gaap:OtherCurrentLiabilitiesMemberus-gaap:DesignatedAsHedgingInstrumentMemberus-gaap:EnergyRelatedDerivativeMemberso:HedgingInstrumentsForRegulatoryPurposesMemberso:SouthernCompanyGasMember2021-03-310000092122us-gaap:DesignatedAsHedgingInstrumentMemberus-gaap:EnergyRelatedDerivativeMemberso:AssetsFromRiskManagementActivitiesMemberso:HedgingInstrumentsForRegulatoryPurposesMemberso:SouthernCompanyGasMember2020-12-310000092122us-gaap:OtherCurrentLiabilitiesMemberus-gaap:DesignatedAsHedgingInstrumentMemberus-gaap:EnergyRelatedDerivativeMemberso:HedgingInstrumentsForRegulatoryPurposesMemberso:SouthernCompanyGasMember2020-12-310000092122us-gaap:DesignatedAsHedgingInstrumentMemberso:HedgingInstrumentsForRegulatoryPurposesMemberso:SouthernCompanyGasMember2021-03-310000092122us-gaap:DesignatedAsHedgingInstrumentMemberso:HedgingInstrumentsForRegulatoryPurposesMemberso:SouthernCompanyGasMember2020-12-310000092122us-gaap:DesignatedAsHedgingInstrumentMemberus-gaap:EnergyRelatedDerivativeMemberso:CashFlowAndFairValueHedgingMemberso:AssetsFromRiskManagementActivitiesMemberso:SouthernCompanyGasMember2021-03-310000092122us-gaap:OtherCurrentLiabilitiesMemberus-gaap:DesignatedAsHedgingInstrumentMemberus-gaap:EnergyRelatedDerivativeMemberso:CashFlowAndFairValueHedgingMemberso:SouthernCompanyGasMember2021-03-310000092122us-gaap:DesignatedAsHedgingInstrumentMemberus-gaap:EnergyRelatedDerivativeMemberso:CashFlowAndFairValueHedgingMemberso:AssetsFromRiskManagementActivitiesMemberso:SouthernCompanyGasMember2020-12-310000092122us-gaap:OtherCurrentLiabilitiesMemberus-gaap:DesignatedAsHedgingInstrumentMemberus-gaap:EnergyRelatedDerivativeMemberso:CashFlowAndFairValueHedgingMemberso:SouthernCompanyGasMember2020-12-310000092122us-gaap:DesignatedAsHedgingInstrumentMemberso:CashFlowAndFairValueHedgingMemberso:SouthernCompanyGasMember2021-03-310000092122us-gaap:DesignatedAsHedgingInstrumentMemberso:CashFlowAndFairValueHedgingMemberso:SouthernCompanyGasMember2020-12-310000092122us-gaap:NondesignatedMemberus-gaap:EnergyRelatedDerivativeMemberso:AssetsFromRiskManagementActivitiesMemberso:SouthernCompanyGasMember2021-03-310000092122us-gaap:OtherCurrentLiabilitiesMemberus-gaap:NondesignatedMemberus-gaap:EnergyRelatedDerivativeMemberso:SouthernCompanyGasMember2021-03-310000092122us-gaap:NondesignatedMemberus-gaap:EnergyRelatedDerivativeMemberso:AssetsFromRiskManagementActivitiesMemberso:SouthernCompanyGasMember2020-12-310000092122us-gaap:OtherCurrentLiabilitiesMemberus-gaap:NondesignatedMemberus-gaap:EnergyRelatedDerivativeMemberso:SouthernCompanyGasMember2020-12-310000092122us-gaap:NondesignatedMemberus-gaap:EnergyRelatedDerivativeMemberso:OtherDeferredChargesAndAssetsMemberso:SouthernCompanyGasMember2021-03-310000092122us-gaap:NondesignatedMemberus-gaap:EnergyRelatedDerivativeMemberso:OtherDeferredCreditsAndLiabilitiesMemberso:SouthernCompanyGasMember2021-03-310000092122us-gaap:NondesignatedMemberus-gaap:EnergyRelatedDerivativeMemberso:OtherDeferredChargesAndAssetsMemberso:SouthernCompanyGasMember2020-12-310000092122us-gaap:NondesignatedMemberus-gaap:EnergyRelatedDerivativeMemberso:OtherDeferredCreditsAndLiabilitiesMemberso:SouthernCompanyGasMember2020-12-310000092122us-gaap:NondesignatedMemberso:SouthernCompanyGasMember2021-03-310000092122us-gaap:NondesignatedMemberso:SouthernCompanyGasMember2020-12-310000092122so:OtherRegulatoryAssetsDeferredMemberus-gaap:EnergyRelatedDerivativeMember2021-03-310000092122so:OtherRegulatoryAssetsDeferredMemberus-gaap:EnergyRelatedDerivativeMemberso:AlabamaPowerMember2021-03-310000092122so:GeorgiaPowerMemberso:OtherRegulatoryAssetsDeferredMemberus-gaap:EnergyRelatedDerivativeMember2021-03-310000092122so:MississippiPowerMemberso:OtherRegulatoryAssetsDeferredMemberus-gaap:EnergyRelatedDerivativeMember2021-03-310000092122so:OtherRegulatoryAssetsDeferredMemberus-gaap:EnergyRelatedDerivativeMemberso:SouthernCompanyGasMember2021-03-310000092122us-gaap:EnergyRelatedDerivativeMemberso:OtherRegulatoryLiabilitiesCurrentMember2021-03-310000092122us-gaap:EnergyRelatedDerivativeMemberso:OtherRegulatoryLiabilitiesCurrentMemberso:AlabamaPowerMember2021-03-310000092122so:GeorgiaPowerMemberus-gaap:EnergyRelatedDerivativeMemberso:OtherRegulatoryLiabilitiesCurrentMember2021-03-310000092122so:MississippiPowerMemberus-gaap:EnergyRelatedDerivativeMemberso:OtherRegulatoryLiabilitiesCurrentMember2021-03-310000092122us-gaap:EnergyRelatedDerivativeMemberso:OtherRegulatoryLiabilitiesCurrentMemberso:SouthernCompanyGasMember2021-03-310000092122us-gaap:EnergyRelatedDerivativeMemberso:OtherRegulatoryLiabilitiesDeferredMember2021-03-310000092122us-gaap:EnergyRelatedDerivativeMemberso:OtherRegulatoryLiabilitiesDeferredMemberso:AlabamaPowerMember2021-03-310000092122so:GeorgiaPowerMemberus-gaap:EnergyRelatedDerivativeMemberso:OtherRegulatoryLiabilitiesDeferredMember2021-03-310000092122so:MississippiPowerMemberus-gaap:EnergyRelatedDerivativeMemberso:OtherRegulatoryLiabilitiesDeferredMember2021-03-310000092122us-gaap:EnergyRelatedDerivativeMemberso:OtherRegulatoryLiabilitiesDeferredMemberso:SouthernCompanyGasMember2021-03-310000092122us-gaap:EnergyRelatedDerivativeMember2021-03-310000092122us-gaap:EnergyRelatedDerivativeMemberso:AlabamaPowerMember2021-03-310000092122so:GeorgiaPowerMemberus-gaap:EnergyRelatedDerivativeMember2021-03-310000092122so:MississippiPowerMemberus-gaap:EnergyRelatedDerivativeMember2021-03-310000092122us-gaap:EnergyRelatedDerivativeMemberso:SouthernCompanyGasMember2021-03-310000092122so:OtherRegulatoryAssetsDeferredMemberus-gaap:EnergyRelatedDerivativeMember2020-12-310000092122so:OtherRegulatoryAssetsDeferredMemberus-gaap:EnergyRelatedDerivativeMemberso:AlabamaPowerMember2020-12-310000092122so:GeorgiaPowerMemberso:OtherRegulatoryAssetsDeferredMemberus-gaap:EnergyRelatedDerivativeMember2020-12-310000092122so:MississippiPowerMemberso:OtherRegulatoryAssetsDeferredMemberus-gaap:EnergyRelatedDerivativeMember2020-12-310000092122so:OtherRegulatoryAssetsDeferredMemberus-gaap:EnergyRelatedDerivativeMemberso:SouthernCompanyGasMember2020-12-310000092122us-gaap:EnergyRelatedDerivativeMemberso:OtherRegulatoryLiabilitiesCurrentMember2020-12-310000092122us-gaap:EnergyRelatedDerivativeMemberso:OtherRegulatoryLiabilitiesCurrentMemberso:AlabamaPowerMember2020-12-310000092122so:GeorgiaPowerMemberus-gaap:EnergyRelatedDerivativeMemberso:OtherRegulatoryLiabilitiesCurrentMember2020-12-310000092122so:MississippiPowerMemberus-gaap:EnergyRelatedDerivativeMemberso:OtherRegulatoryLiabilitiesCurrentMember2020-12-310000092122us-gaap:EnergyRelatedDerivativeMemberso:OtherRegulatoryLiabilitiesCurrentMemberso:SouthernCompanyGasMember2020-12-310000092122us-gaap:EnergyRelatedDerivativeMemberso:OtherRegulatoryLiabilitiesDeferredMember2020-12-310000092122us-gaap:EnergyRelatedDerivativeMemberso:OtherRegulatoryLiabilitiesDeferredMemberso:AlabamaPowerMember2020-12-310000092122so:GeorgiaPowerMemberus-gaap:EnergyRelatedDerivativeMemberso:OtherRegulatoryLiabilitiesDeferredMember2020-12-310000092122so:MississippiPowerMemberus-gaap:EnergyRelatedDerivativeMemberso:OtherRegulatoryLiabilitiesDeferredMember2020-12-310000092122us-gaap:EnergyRelatedDerivativeMemberso:OtherRegulatoryLiabilitiesDeferredMemberso:SouthernCompanyGasMember2020-12-310000092122us-gaap:EnergyRelatedDerivativeMember2020-12-310000092122us-gaap:EnergyRelatedDerivativeMemberso:AlabamaPowerMember2020-12-310000092122so:GeorgiaPowerMemberus-gaap:EnergyRelatedDerivativeMember2020-12-310000092122so:MississippiPowerMemberus-gaap:EnergyRelatedDerivativeMember2020-12-310000092122us-gaap:EnergyRelatedDerivativeMemberso:SouthernCompanyGasMember2020-12-310000092122us-gaap:EnergyRelatedDerivativeMember2021-01-012021-03-310000092122us-gaap:EnergyRelatedDerivativeMember2020-01-012020-03-310000092122us-gaap:InterestRateContractMember2021-01-012021-03-310000092122us-gaap:InterestRateContractMember2020-01-012020-03-310000092122us-gaap:ForeignExchangeContractMember2021-01-012021-03-310000092122us-gaap:ForeignExchangeContractMember2020-01-012020-03-310000092122us-gaap:EnergyRelatedDerivativeMemberso:SouthernPowerMember2021-01-012021-03-310000092122us-gaap:EnergyRelatedDerivativeMemberso:SouthernPowerMember2020-01-012020-03-310000092122us-gaap:ForeignExchangeContractMemberso:SouthernPowerMember2021-01-012021-03-310000092122us-gaap:ForeignExchangeContractMemberso:SouthernPowerMember2020-01-012020-03-310000092122us-gaap:EnergyRelatedDerivativeMemberso:SouthernCompanyGasMember2021-01-012021-03-310000092122us-gaap:EnergyRelatedDerivativeMemberso:SouthernCompanyGasMember2020-01-012020-03-310000092122us-gaap:InterestRateContractMemberso:SouthernCompanyGasMember2021-01-012021-03-310000092122us-gaap:InterestRateContractMemberso:SouthernCompanyGasMember2020-01-012020-03-310000092122us-gaap:EnergyRelatedDerivativeMemberus-gaap:CostOfSalesMemberus-gaap:CashFlowHedgingMember2021-01-012021-03-310000092122us-gaap:EnergyRelatedDerivativeMemberus-gaap:CostOfSalesMemberus-gaap:CashFlowHedgingMember2020-01-012020-03-310000092122us-gaap:EnergyRelatedDerivativeMemberso:DepreciationandAmortizationMemberus-gaap:CashFlowHedgingMember2021-01-012021-03-310000092122us-gaap:EnergyRelatedDerivativeMemberso:DepreciationandAmortizationMemberus-gaap:CashFlowHedgingMember2020-01-012020-03-310000092122us-gaap:InterestExpenseMemberus-gaap:InterestRateContractMemberus-gaap:CashFlowHedgingMember2021-01-012021-03-310000092122us-gaap:InterestExpenseMemberus-gaap:InterestRateContractMemberus-gaap:CashFlowHedgingMember2020-01-012020-03-310000092122us-gaap:ForeignExchangeContractMemberus-gaap:InterestExpenseMemberus-gaap:CashFlowHedgingMember2021-01-012021-03-310000092122us-gaap:ForeignExchangeContractMemberus-gaap:InterestExpenseMemberus-gaap:CashFlowHedgingMember2020-01-012020-03-310000092122us-gaap:InterestExpenseMemberus-gaap:InterestRateContractMemberus-gaap:FairValueHedgingMember2021-01-012021-03-310000092122us-gaap:InterestExpenseMemberus-gaap:InterestRateContractMemberus-gaap:FairValueHedgingMember2020-01-012020-03-310000092122us-gaap:ForeignExchangeContractMemberus-gaap:OtherNonoperatingIncomeExpenseMemberus-gaap:CashFlowHedgingMember2021-01-012021-03-310000092122us-gaap:ForeignExchangeContractMemberus-gaap:OtherNonoperatingIncomeExpenseMemberus-gaap:CashFlowHedgingMember2020-01-012020-03-310000092122us-gaap:EnergyRelatedDerivativeMemberso:DepreciationandAmortizationMemberso:SouthernPowerMemberus-gaap:CashFlowHedgingMember2021-01-012021-03-310000092122us-gaap:EnergyRelatedDerivativeMemberso:DepreciationandAmortizationMemberso:SouthernPowerMemberus-gaap:CashFlowHedgingMember2020-01-012020-03-310000092122us-gaap:ForeignExchangeContractMemberus-gaap:InterestExpenseMemberso:SouthernPowerMemberus-gaap:CashFlowHedgingMember2021-01-012021-03-310000092122us-gaap:ForeignExchangeContractMemberus-gaap:InterestExpenseMemberso:SouthernPowerMemberus-gaap:CashFlowHedgingMember2020-01-012020-03-310000092122us-gaap:ForeignExchangeContractMemberus-gaap:OtherNonoperatingIncomeExpenseMemberso:SouthernPowerMemberus-gaap:CashFlowHedgingMember2021-01-012021-03-310000092122us-gaap:ForeignExchangeContractMemberus-gaap:OtherNonoperatingIncomeExpenseMemberso:SouthernPowerMemberus-gaap:CashFlowHedgingMember2020-01-012020-03-310000092122us-gaap:ShortTermDebtMemberus-gaap:FairValueHedgingMember2021-03-310000092122us-gaap:ShortTermDebtMemberus-gaap:FairValueHedgingMember2020-12-310000092122us-gaap:NondesignatedMemberso:NaturalGasRevenuesMemberus-gaap:EnergyRelatedDerivativeMember2021-01-012021-03-310000092122us-gaap:NondesignatedMemberso:NaturalGasRevenuesMemberus-gaap:EnergyRelatedDerivativeMember2020-01-012020-03-310000092122us-gaap:NondesignatedMemberus-gaap:EnergyRelatedDerivativeMemberso:CostofNaturalGasMember2021-01-012021-03-310000092122us-gaap:NondesignatedMemberus-gaap:EnergyRelatedDerivativeMemberso:CostofNaturalGasMember2020-01-012020-03-310000092122us-gaap:NondesignatedMemberus-gaap:EnergyRelatedDerivativeMember2021-01-012021-03-310000092122us-gaap:NondesignatedMemberus-gaap:EnergyRelatedDerivativeMember2020-01-012020-03-310000092122so:RegistrantsMemberso:DerivativeCounterpartiesMember2021-03-310000092122us-gaap:DisposalGroupHeldforsaleNotDiscontinuedOperationsMember2021-03-310000092122us-gaap:DisposalGroupHeldforsaleNotDiscontinuedOperationsMember2020-12-310000092122so:SouthernPowerMemberso:DeuelHarvestMember2021-02-280000092122so:DeuelHarvestMemberso:SouthernPowerMemberso:DeuelHarvestMember2021-02-280000092122so:SouthernPowerMembersrt:MaximumMemberso:DeuelHarvestMember2021-02-012021-02-280000092122srt:MinimumMemberso:SouthernPowerMemberso:DeuelHarvestMember2021-02-012021-02-280000092122so:SouthernPowerMemberso:DeuelHarvestMember2021-03-302021-03-300000092122srt:MinimumMemberso:SouthernPowerMemberso:SeriesofConstructionProjectsMember2021-03-310000092122so:SouthernPowerMembersrt:MaximumMemberso:SeriesofConstructionProjectsMember2021-03-310000092122so:SouthernPowerMemberso:SeriesofConstructionProjectsMember2021-03-310000092122so:SouthernPowerMembersrt:ScenarioForecastMemberso:GarlandSolarStorageMember2021-12-310000092122so:SouthernPowerMembersrt:ScenarioForecastMemberso:GarlandSolarStorageMember2021-10-012021-12-310000092122so:TranquillitySolarStorageMemberso:SouthernPowerMembersrt:ScenarioForecastMember2021-12-310000092122so:TranquillitySolarStorageMemberso:SouthernPowerMembersrt:ScenarioForecastMember2021-10-012021-12-310000092122so:SouthernPowerMembersrt:ScenarioForecastMemberso:GlassSandsMember2021-12-310000092122so:SouthernPowerMembersrt:ScenarioForecastMemberso:GlassSandsMember2021-10-012021-12-310000092122so:GarlandSolarStorageMemberso:SouthernPowerMemberso:GarlandSolarStorageMemberso:ClassBMembershipInterestMember2020-12-012020-12-310000092122so:TranquillitySolarStorageMemberso:SouthernPowerMemberso:TranquillitySolarStorageMemberso:ClassBMembershipInterestMember2020-12-012020-12-310000092122so:GlassSandsMemberso:SouthernPowerMemberso:GlassSandsMember2020-12-310000092122so:SouthernPowerMemberso:WindGeneratingFacilityMember2021-01-012021-03-310000092122us-gaap:SubsequentEventMemberso:SequentMemberso:SouthernCompanyGasMemberus-gaap:DisposalGroupDisposedOfBySaleNotDiscontinuedOperationsMember2021-04-280000092122so:SequentMemberso:SouthernCompanyGasMemberus-gaap:DisposalGroupDisposedOfBySaleNotDiscontinuedOperationsMember2021-03-31so:payment0000092122so:SouthernCompanyGasMemberus-gaap:DisposalGroupDisposedOfBySaleNotDiscontinuedOperationsMemberso:PivotalLNGMember2020-03-310000092122srt:ScenarioForecastMemberso:SouthernCompanyGasMemberus-gaap:DisposalGroupDisposedOfBySaleNotDiscontinuedOperationsMemberso:PivotalLNGMember2021-04-220000092122srt:ScenarioForecastMemberso:SouthernCompanyGasMemberus-gaap:DisposalGroupDisposedOfBySaleNotDiscontinuedOperationsMemberso:PivotalLNGMember2021-08-31so:state0000092122so:SouthernPowerMemberso:TraditionalElectricOperatingCompaniesMemberso:WholesaleAffiliatesMember2021-01-012021-03-310000092122so:SouthernPowerMemberso:TraditionalElectricOperatingCompaniesMemberso:WholesaleAffiliatesMember2020-01-012020-03-310000092122so:SouthernPowerMemberus-gaap:NaturalGasUsRegulatedMemberso:SouthernCompanyGasMember2021-01-012021-03-310000092122so:SouthernPowerMemberus-gaap:NaturalGasUsRegulatedMemberso:SouthernCompanyGasMember2020-01-012020-03-310000092122so:ElectricUtilitiesMemberso:TraditionalElectricOperatingCompaniesMemberus-gaap:OperatingSegmentsMember2021-01-012021-03-310000092122so:ElectricUtilitiesMemberso:SouthernPowerMemberus-gaap:OperatingSegmentsMember2021-01-012021-03-310000092122so:ElectricUtilitiesMemberus-gaap:IntersegmentEliminationMember2021-01-012021-03-310000092122so:ElectricUtilitiesMember2021-01-012021-03-310000092122so:SouthernCompanyGasMemberus-gaap:OperatingSegmentsMember2021-01-012021-03-310000092122us-gaap:OperatingSegmentsMemberus-gaap:CorporateAndOtherMember2021-01-012021-03-310000092122us-gaap:IntersegmentEliminationMember2021-01-012021-03-310000092122so:ElectricUtilitiesMemberso:TraditionalElectricOperatingCompaniesMemberus-gaap:OperatingSegmentsMember2021-03-310000092122so:ElectricUtilitiesMemberso:SouthernPowerMemberus-gaap:OperatingSegmentsMember2021-03-310000092122so:ElectricUtilitiesMemberus-gaap:IntersegmentEliminationMember2021-03-310000092122so:ElectricUtilitiesMember2021-03-310000092122so:SouthernCompanyGasMemberus-gaap:OperatingSegmentsMember2021-03-310000092122us-gaap:OperatingSegmentsMemberus-gaap:CorporateAndOtherMember2021-03-310000092122us-gaap:IntersegmentEliminationMember2021-03-310000092122so:ElectricUtilitiesMemberso:TraditionalElectricOperatingCompaniesMemberus-gaap:OperatingSegmentsMember2020-01-012020-03-310000092122so:ElectricUtilitiesMemberso:SouthernPowerMemberus-gaap:OperatingSegmentsMember2020-01-012020-03-310000092122so:ElectricUtilitiesMemberus-gaap:IntersegmentEliminationMember2020-01-012020-03-310000092122so:ElectricUtilitiesMember2020-01-012020-03-310000092122so:SouthernCompanyGasMemberus-gaap:OperatingSegmentsMember2020-01-012020-03-310000092122us-gaap:OperatingSegmentsMemberus-gaap:CorporateAndOtherMember2020-01-012020-03-310000092122us-gaap:IntersegmentEliminationMember2020-01-012020-03-310000092122so:ElectricUtilitiesMemberso:TraditionalElectricOperatingCompaniesMemberus-gaap:OperatingSegmentsMember2020-12-310000092122so:ElectricUtilitiesMemberso:SouthernPowerMemberus-gaap:OperatingSegmentsMember2020-12-310000092122so:ElectricUtilitiesMemberus-gaap:IntersegmentEliminationMember2020-12-310000092122so:ElectricUtilitiesMember2020-12-310000092122so:SouthernCompanyGasMemberus-gaap:OperatingSegmentsMember2020-12-310000092122us-gaap:OperatingSegmentsMemberus-gaap:CorporateAndOtherMember2020-12-310000092122us-gaap:IntersegmentEliminationMember2020-12-310000092122so:MankatoMemberso:SouthernPowerMemberus-gaap:DisposalGroupDisposedOfBySaleNotDiscontinuedOperationsMember2020-01-012020-03-310000092122us-gaap:RetailMemberso:ElectricUtilitiesMember2021-01-012021-03-310000092122so:WholesaleNonAffiliatesMemberso:ElectricUtilitiesMember2021-01-012021-03-310000092122so:ElectricUtilitiesMemberso:OtherElectricRevenueMember2021-01-012021-03-310000092122so:ElectricUtilitiesMember2021-01-012021-03-310000092122us-gaap:RetailMemberso:ElectricUtilitiesMember2020-01-012020-03-310000092122so:WholesaleNonAffiliatesMemberso:ElectricUtilitiesMember2020-01-012020-03-310000092122so:ElectricUtilitiesMemberso:OtherElectricRevenueMember2020-01-012020-03-310000092122so:ElectricUtilitiesMember2020-01-012020-03-310000092122so:NaturalGasDistributionMemberso:SouthernCompanyGasMember2021-01-012021-03-310000092122so:SouthernCompanyGasMemberso:WholesaleGasServicesMember2021-01-012021-03-310000092122so:SouthernCompanyGasMemberso:GasMarketingServicesMember2021-01-012021-03-310000092122so:NaturalGasDistributionOtherMemberso:SouthernCompanyGasMember2021-01-012021-03-310000092122so:SouthernCompanyGasMember2021-01-012021-03-310000092122so:NaturalGasDistributionMemberso:SouthernCompanyGasMember2020-01-012020-03-310000092122so:SouthernCompanyGasMemberso:WholesaleGasServicesMember2020-01-012020-03-310000092122so:SouthernCompanyGasMemberso:GasMarketingServicesMember2020-01-012020-03-310000092122so:NaturalGasDistributionOtherMemberso:SouthernCompanyGasMember2020-01-012020-03-310000092122so:SouthernCompanyGasMember2020-01-012020-03-31so:segment0000092122so:SouthernNaturalGasCompanyLLCMemberso:SouthernCompanyGasMember2021-03-310000092122so:PennEastPipelinesMemberso:SouthernCompanyGasMember2021-03-310000092122so:DaltonPipelineMemberso:SouthernCompanyGasMember2021-03-310000092122so:AtlanticCoastPipelineMemberso:SouthernCompanyGasMember2021-03-310000092122so:GasDistributionOperationsMemberso:SouthernCompanyGasMemberus-gaap:OperatingSegmentsMember2021-01-012021-03-310000092122so:GasPipelineInvestmentsMemberso:SouthernCompanyGasMemberus-gaap:OperatingSegmentsMember2021-01-012021-03-310000092122so:WholesaleGasServicesMemberso:SouthernCompanyGasMemberus-gaap:OperatingSegmentsMember2021-01-012021-03-310000092122so:GasMarketingServicesMemberso:SouthernCompanyGasMemberus-gaap:OperatingSegmentsMember2021-01-012021-03-310000092122so:SouthernCompanyGasMemberus-gaap:OperatingSegmentsMember2021-01-012021-03-310000092122so:SouthernCompanyGasMemberus-gaap:OperatingSegmentsMemberus-gaap:CorporateAndOtherMember2021-01-012021-03-310000092122us-gaap:IntersegmentEliminationMemberso:SouthernCompanyGasMember2021-01-012021-03-310000092122so:GasDistributionOperationsMemberso:SouthernCompanyGasMemberus-gaap:OperatingSegmentsMember2021-03-310000092122so:GasPipelineInvestmentsMemberso:SouthernCompanyGasMemberus-gaap:OperatingSegmentsMember2021-03-310000092122so:WholesaleGasServicesMemberso:SouthernCompanyGasMemberus-gaap:OperatingSegmentsMember2021-03-310000092122so:GasMarketingServicesMemberso:SouthernCompanyGasMemberus-gaap:OperatingSegmentsMember2021-03-310000092122so:SouthernCompanyGasMemberus-gaap:OperatingSegmentsMember2021-03-310000092122so:SouthernCompanyGasMemberus-gaap:OperatingSegmentsMemberus-gaap:CorporateAndOtherMember2021-03-310000092122us-gaap:IntersegmentEliminationMemberso:SouthernCompanyGasMember2021-03-310000092122so:GasDistributionOperationsMemberso:SouthernCompanyGasMemberus-gaap:OperatingSegmentsMember2020-01-012020-03-310000092122so:GasPipelineInvestmentsMemberso:SouthernCompanyGasMemberus-gaap:OperatingSegmentsMember2020-01-012020-03-310000092122so:WholesaleGasServicesMemberso:SouthernCompanyGasMemberus-gaap:OperatingSegmentsMember2020-01-012020-03-310000092122so:GasMarketingServicesMemberso:SouthernCompanyGasMemberus-gaap:OperatingSegmentsMember2020-01-012020-03-310000092122so:SouthernCompanyGasMemberus-gaap:OperatingSegmentsMember2020-01-012020-03-310000092122so:SouthernCompanyGasMemberus-gaap:OperatingSegmentsMemberus-gaap:CorporateAndOtherMember2020-01-012020-03-310000092122us-gaap:IntersegmentEliminationMemberso:SouthernCompanyGasMember2020-01-012020-03-310000092122so:GasDistributionOperationsMemberso:SouthernCompanyGasMemberus-gaap:OperatingSegmentsMember2020-12-310000092122so:GasPipelineInvestmentsMemberso:SouthernCompanyGasMemberus-gaap:OperatingSegmentsMember2020-12-310000092122so:WholesaleGasServicesMemberso:SouthernCompanyGasMemberus-gaap:OperatingSegmentsMember2020-12-310000092122so:GasMarketingServicesMemberso:SouthernCompanyGasMemberus-gaap:OperatingSegmentsMember2020-12-310000092122so:SouthernCompanyGasMemberus-gaap:OperatingSegmentsMember2020-12-310000092122so:SouthernCompanyGasMemberus-gaap:OperatingSegmentsMemberus-gaap:CorporateAndOtherMember2020-12-310000092122us-gaap:IntersegmentEliminationMemberso:SouthernCompanyGasMember2020-12-310000092122so:ThirdPartyGrossRevenuesMemberso:WholesaleGasServicesMemberso:SouthernCompanyGasMember2021-01-012021-03-310000092122so:IntercompanyRevenuesMemberso:WholesaleGasServicesMemberso:SouthernCompanyGasMember2021-01-012021-03-310000092122so:TotalGrossRevenuesMemberso:WholesaleGasServicesMemberso:SouthernCompanyGasMember2021-01-012021-03-310000092122so:WholesaleGasServicesMemberso:SouthernCompanyGasMember2021-01-012021-03-310000092122so:ThirdPartyGrossRevenuesMemberso:WholesaleGasServicesMemberso:SouthernCompanyGasMember2020-01-012020-03-310000092122so:IntercompanyRevenuesMemberso:WholesaleGasServicesMemberso:SouthernCompanyGasMember2020-01-012020-03-310000092122so:TotalGrossRevenuesMemberso:WholesaleGasServicesMemberso:SouthernCompanyGasMember2020-01-012020-03-310000092122so:WholesaleGasServicesMemberso:SouthernCompanyGasMember2020-01-012020-03-31
    Table of Contents                                Index to Financial Statements
UNITED STATES
SECURITIES AND EXCHANGE COMMISSION
Washington, D.C. 20549
FORM 10-Q
QUARTERLY REPORT PURSUANT TO SECTION 13 OR 15(d)
OF THE SECURITIES EXCHANGE ACT OF 1934
For the quarterly period ended March 31, 2021
OR
TRANSITION REPORT PURSUANT TO SECTION 13 OR 15(d)
OF THE SECURITIES EXCHANGE ACT OF 1934
For the transition period from           to            
Commission
File Number
Registrant,
State of Incorporation,
Address and Telephone Number
I.R.S. Employer
Identification No.
1-3526The Southern Company58-0690070
(A Delaware Corporation)
30 Ivan Allen Jr. Boulevard, N.W.
Atlanta, Georgia 30308
(404) 506-5000
1-3164Alabama Power Company63-0004250
(An Alabama Corporation)
600 North 18th Street
Birmingham, Alabama 35203
(205) 257-1000
1-6468Georgia Power Company58-0257110
(A Georgia Corporation)
241 Ralph McGill Boulevard, N.E.
Atlanta, Georgia 30308
(404) 506-6526
001-11229Mississippi Power Company64-0205820
(A Mississippi Corporation)
2992 West Beach Boulevard
Gulfport, Mississippi 39501
(228) 864-1211
001-37803Southern Power Company58-2598670
(A Delaware Corporation)
30 Ivan Allen Jr. Boulevard, N.W.
Atlanta, Georgia 30308
(404) 506-5000
1-14174Southern Company Gas58-2210952
(A Georgia Corporation)
Ten Peachtree Place, N.E.
Atlanta, Georgia 30309
(404) 584-4000


    Table of Contents                                Index to Financial Statements
Securities registered pursuant to Section 12(b) of the Act:
RegistrantTitle of Each ClassTrading
Symbol(s)
Name of Each Exchange
on Which Registered
The Southern CompanyCommon Stock, par value $5 per shareSONew York Stock Exchange
(NYSE)
The Southern CompanySeries 2016A 5.25% Junior Subordinated Notes due 2076SOJBNYSE
The Southern CompanySeries 2017B 5.25% Junior Subordinated Notes due 2077SOJCNYSE
The Southern Company2019 Series A Corporate UnitsSOLNNYSE
The Southern CompanySeries 2020A 4.95% Junior Subordinated Notes due 2080SOJDNYSE
The Southern CompanySeries 2020C 4.20% Junior Subordinated Notes due 2060SOJENYSE
Alabama Power Company5.00% Series Class A Preferred StockALP PR QNYSE
Georgia Power CompanySeries 2017A 5.00% Junior Subordinated Notes due 2077GPJANYSE
Southern Power CompanySeries 2016A 1.000% Senior Notes due 2022SO/22BNYSE
Southern Power CompanySeries 2016B 1.850% Senior Notes due 2026SO/26ANYSE
Indicate by check mark whether the registrants (1) have filed all reports required to be filed by Section 13 or 15(d) of the Securities Exchange Act of 1934 during the preceding 12 months (or for such shorter period that the registrants were required to file such reports), and (2) have been subject to such filing requirements for the past 90 days. Yes þ No ¨
Indicate by check mark whether the registrants have submitted electronically every Interactive Data File required to be submitted pursuant to Rule 405 of Regulation S-T during the preceding 12 months (or for such shorter period that the registrants were required to submit such files). Yes þ No ¨
Indicate by check mark whether the registrant is a large accelerated filer, an accelerated filer, a non-accelerated filer, a smaller reporting company, or an emerging growth company. See the definitions of "large accelerated filer," "accelerated filer," "smaller reporting company," and "emerging growth company" in Rule 12b-2 of the Exchange Act.
RegistrantLarge Accelerated FilerAccelerated
Filer
Non-accelerated FilerSmaller
Reporting
Company
Emerging
Growth
Company
The Southern CompanyX
Alabama Power CompanyX
Georgia Power CompanyX
Mississippi Power CompanyX
Southern Power CompanyX
Southern Company GasX
If an emerging growth company, indicate by check mark if the registrant has elected not to use the extended transition period for complying with any new or revised financial accounting standards provided pursuant to Section 13(a) of the Exchange Act.
Indicate by check mark whether the registrant is a shell company (as defined in Rule 12b-2 of the Exchange Act). Yes No þ (Response applicable to all registrants.)
RegistrantDescription of Common Stock
Shares Outstanding at March 31, 2021
The Southern CompanyPar Value $5 Per Share1,058,630,385 
Alabama Power CompanyPar Value $40 Per Share30,537,500 
Georgia Power CompanyWithout Par Value9,261,500 
Mississippi Power CompanyWithout Par Value1,121,000 
Southern Power CompanyPar Value $0.01 Per Share1,000 
Southern Company GasPar Value $0.01 Per Share100 
This combined Form 10-Q is separately filed by The Southern Company, Alabama Power Company, Georgia Power Company, Mississippi Power Company, Southern Power Company, and Southern Company Gas. Information contained herein relating to any individual registrant is filed by such registrant on its own behalf. Each registrant makes no representation as to information relating to the other registrants.
2

    Table of Contents                                Index to Financial Statements
TABLE OF CONTENTS
  Page
PART I—FINANCIAL INFORMATION
Item 1.
Item 2.
Item 3.
Item 4.
PART II—OTHER INFORMATION
Item 1.
Item 1A.
Item 2.Unregistered Sales of Equity Securities and Use of ProceedsInapplicable
Item 3.Defaults Upon Senior SecuritiesInapplicable
Item 4.Mine Safety DisclosuresInapplicable
Item 5.Other InformationInapplicable
Item 6.
3

    Table of Contents                                Index to Financial Statements

DEFINITIONS
TermMeaning
2019 ARPAlternate Rate Plan approved by the Georgia PSC in 2019 for Georgia Power for the years 2020 through 2022
AFUDCAllowance for funds used during construction
Alabama PowerAlabama Power Company
Amended and Restated Loan Guarantee AgreementLoan guarantee agreement entered into by Georgia Power with the DOE in 2014, as amended and restated in March 2019, under which the proceeds of borrowings may be used to reimburse Georgia Power for Eligible Project Costs incurred in connection with its construction of Plant Vogtle Units 3 and 4
AROAsset retirement obligation
Atlanta Gas LightAtlanta Gas Light Company, a wholly-owned subsidiary of Southern Company Gas
Atlantic Coast PipelineAtlantic Coast Pipeline, LLC, a joint venture to construct and operate a natural gas pipeline in which Southern Company Gas held a 5% interest through March 24, 2020
BechtelBechtel Power Corporation, the primary contractor for the remaining construction activities for Plant Vogtle Units 3 and 4
Bechtel AgreementThe 2017 construction completion agreement between the Vogtle Owners and Bechtel
CCRCoal combustion residuals
Chattanooga GasChattanooga Gas Company, a wholly-owned subsidiary of Southern Company Gas
CODCommercial operation date
Contractor Settlement AgreementThe December 31, 2015 agreement between Westinghouse and the Vogtle Owners resolving disputes between the Vogtle Owners and the EPC Contractor under the Vogtle 3 and 4 Agreement
COVID-19The novel coronavirus disease declared a pandemic by the World Health Organization and the Centers for Disease Control and Prevention in March 2020
CWIPConstruction work in progress
DaltonCity of Dalton, Georgia, an incorporated municipality in the State of Georgia, acting by and through its Board of Water, Light, and Sinking Fund Commissioners
Dalton PipelineA pipeline facility in Georgia in which Southern Company Gas has a 50% undivided ownership interest
DOEU.S. Department of Energy
ECO PlanMississippi Power's environmental compliance overview plan
Eligible Project CostsCertain costs of construction relating to Plant Vogtle Units 3 and 4 that are eligible for financing under the loan guarantee program established under Title XVII of the Energy Policy Act of 2005
EPAU.S. Environmental Protection Agency
EPC ContractorWestinghouse and its affiliate, WECTEC Global Project Services Inc.; the former engineering, procurement, and construction contractor for Plant Vogtle Units 3 and 4
FERCFederal Energy Regulatory Commission
FFBFederal Financing Bank
FFB Credit FacilitiesNote purchase agreements among the DOE, Georgia Power, and the FFB and related promissory notes which provide for two multi-advance term loan facilities
FitchFitch Ratings, Inc.
Form 10-KAnnual Report on Form 10-K of Southern Company, Alabama Power, Georgia Power, Mississippi Power, Southern Power, and Southern Company Gas for the year ended December 31, 2020, as applicable
GAAPU.S. generally accepted accounting principles
Georgia PowerGeorgia Power Company
GRAMAtlanta Gas Light's Georgia Rate Adjustment Mechanism
Guarantee Settlement AgreementThe June 9, 2017 settlement agreement between the Vogtle Owners and Toshiba related to certain payment obligations of the EPC Contractor guaranteed by Toshiba
4

    Table of Contents                                Index to Financial Statements

DEFINITIONS
(continued)
TermMeaning
Gulf PowerGulf Power Company, until January 1, 2019 a wholly-owned subsidiary of Southern Company; effective January 1, 2021, Gulf Power Company merged with and into Florida Power and Light Company, with Florida Power and Light Company remaining as the surviving company
Heating Degree DaysA measure of weather, calculated when the average daily temperatures are less than 65 degrees Fahrenheit
Heating SeasonThe period from November through March when Southern Company Gas' natural gas usage and operating revenues are generally higher
HLBVHypothetical liquidation at book value
IGCCIntegrated coal gasification combined cycle, the technology originally approved for Mississippi Power's Kemper County energy facility
IICIntercompany Interchange Contract
IRPIntegrated resource plan
ITAACInspections, Tests, Analyses, and Acceptance Criteria, standards established by the NRC
ITCInvestment tax credit
JEAJacksonville Electric Authority
Jefferson Island
Jefferson Island Storage and Hub, L.L.C, which owns a natural gas storage facility in Louisiana consisting of two salt dome caverns; a subsidiary of Southern Company Gas through December 1, 2020
KWHKilowatt-hour
LIBORLondon Interbank Offered Rate
LIFOLast-in, first-out
LOCOMLower of weighted average cost or current market price
LTSALong-term service agreement
MarketersMarketers selling retail natural gas in Georgia and certificated by the Georgia PSC
MEAG PowerMunicipal Electric Authority of Georgia
Mississippi PowerMississippi Power Company
Mississippi Power Rate Case Settlement AgreementSettlement agreement between Mississippi Power and the Mississippi Public
Utilities Staff approved by the Mississippi PSC in March 2020 related to Mississippi Power's base rate case filed in 2019
mmBtuMillion British thermal units
Moody'sMoody's Investors Service, Inc.
MRAMunicipal and Rural Associations
MWMegawatt
natural gas distribution utilitiesSouthern Company Gas' natural gas distribution utilities (Nicor Gas, Atlanta Gas Light, Virginia Natural Gas, and Chattanooga Gas)
NCCRGeorgia Power's Nuclear Construction Cost Recovery
Nicor GasNorthern Illinois Gas Company, a wholly-owned subsidiary of Southern Company Gas
NRCU.S. Nuclear Regulatory Commission
NYMEXNew York Mercantile Exchange, Inc.
OCIOther comprehensive income
PennEast PipelinePennEast Pipeline Company, LLC, a joint venture to construct and operate a natural gas pipeline in which Southern Company Gas has a 20% ownership interest
PEPMississippi Power's Performance Evaluation Plan
Pivotal LNGPivotal LNG, Inc., through March 24, 2020, a wholly-owned subsidiary of Southern Company Gas
PowerSecurePowerSecure, Inc., a wholly-owned subsidiary of Southern Company
PowerSouthPowerSouth Energy Cooperative
PPAPower purchase agreements, as well as, for Southern Power, contracts for differences that provide the owner of a renewable facility a certain fixed price for the electricity sold to the grid
5

    Table of Contents                                Index to Financial Statements

DEFINITIONS
(continued)
TermMeaning
PSCPublic Service Commission
PTCProduction tax credit
Rate CNPAlabama Power's Rate Certificated New Plant, consisting of Rate CNP New Plant, Rate CNP Compliance, and Rate CNP PPA
Rate ECRAlabama Power's Rate Energy Cost Recovery
Rate RSEAlabama Power's Rate Stabilization and Equalization
RegistrantsSouthern Company, Alabama Power, Georgia Power, Mississippi Power, Southern Power Company, and Southern Company Gas
ROEReturn on equity
S&PS&P Global Ratings, a division of S&P Global Inc.
SCSSouthern Company Services, Inc., the Southern Company system service company and a wholly-owned subsidiary of Southern Company
SECU.S. Securities and Exchange Commission
SEGCOSouthern Electric Generating Company, 50% owned by each of Alabama Power and Georgia Power
SequentSequent Energy Management, L.P. and Sequent Energy Canada Corp., wholly-owned subsidiaries of Southern Company Gas
SNGSouthern Natural Gas Company, L.L.C., a pipeline system in which Southern Company Gas has a 50% ownership interest
Southern CompanyThe Southern Company
Southern Company GasSouthern Company Gas and its subsidiaries
Southern Company Gas CapitalSouthern Company Gas Capital Corporation, a 100%-owned subsidiary of Southern Company Gas
Southern Company power poolThe operating arrangement whereby the integrated generating resources of the traditional electric operating companies and Southern Power (excluding subsidiaries) are subject to joint commitment and dispatch in order to serve their combined load obligations
Southern Company systemSouthern Company, the traditional electric operating companies, Southern Power, Southern Company Gas, Southern Electric Generating Company, Southern Nuclear, SCS, Southern Communications Services, Inc., PowerSecure, and other subsidiaries
Southern HoldingsSouthern Company Holdings, Inc., a wholly-owned subsidiary of Southern Company
Southern NuclearSouthern Nuclear Operating Company, Inc., a wholly-owned subsidiary of Southern Company
Southern PowerSouthern Power Company and its subsidiaries
SouthStarSouthStar Energy Services, LLC (a Marketer), a wholly-owned subsidiary of Southern Company Gas
SP SolarSP Solar Holdings I, LP, a limited partnership indirectly owning substantially all of Southern Power's solar facilities, in which Southern Power has a 67% ownership interest
SP WindSP Wind Holdings II, LLC, a holding company owning a portfolio of eight operating wind facilities, in which Southern Power is the controlling partner in a tax equity arrangement
Subsidiary RegistrantsAlabama Power, Georgia Power, Mississippi Power, Southern Power, and Southern Company Gas
Tax ReformThe impact of the Tax Cuts and Jobs Act, which became effective on January 1, 2018
ToshibaToshiba Corporation, the parent company of Westinghouse
traditional electric operating companiesAlabama Power, Georgia Power, and Mississippi Power
VCMVogtle Construction Monitoring
VIEVariable interest entity
Virginia Natural GasVirginia Natural Gas, Inc., a wholly-owned subsidiary of Southern Company Gas
Vogtle 3 and 4 AgreementAgreement entered into with the EPC Contractor in 2008 by Georgia Power, acting for itself and as agent for the Vogtle Owners, and rejected in bankruptcy in July 2017, pursuant to which the EPC Contractor agreed to design, engineer, procure, construct, and test Plant Vogtle Units 3 and 4
6

    Table of Contents                                Index to Financial Statements

DEFINITIONS
(continued)
TermMeaning
Vogtle OwnersGeorgia Power, Oglethorpe Power Corporation, MEAG Power, and Dalton
Vogtle Services AgreementThe June 2017 services agreement between the Vogtle Owners and the EPC Contractor, as amended and restated in July 2017, for the EPC Contractor to transition construction management of Plant Vogtle Units 3 and 4 to Southern Nuclear and to provide ongoing design, engineering, and procurement services to Southern Nuclear
WACOGWeighted average cost of gas
WestinghouseWestinghouse Electric Company LLC
7

    Table of Contents                                Index to Financial Statements
CAUTIONARY STATEMENT REGARDING FORWARD-LOOKING INFORMATION
This Quarterly Report on Form 10-Q contains forward-looking statements. Forward-looking statements include, among other things, statements concerning the potential and expected effects of the COVID-19 pandemic, regulated rates, the strategic goals for the business, customer and sales growth, economic conditions, cost recovery and other rate actions, projected equity ratios, current and proposed environmental regulations and related compliance plans and estimated expenditures, pending or potential litigation matters, access to sources of capital, financing activities, completion dates and costs of construction projects, matters related to the abandonment of the Kemper IGCC, completion of announced dispositions, filings with state and federal regulatory authorities, and estimated construction plans and expenditures. In some cases, forward-looking statements can be identified by terminology such as "may," "will," "could," "would," "should," "expects," "plans," "anticipates," "believes," "estimates," "projects," "predicts," "potential," or "continue" or the negative of these terms or other similar terminology. There are various factors that could cause actual results to differ materially from those suggested by the forward-looking statements; accordingly, there can be no assurance that such indicated results will be realized. These factors include:

the impact of recent and future federal and state regulatory changes, including tax, environmental, and other laws and regulations to which Southern Company and its subsidiaries are subject, as well as changes in application of existing laws and regulations;
the potential effects of the continued COVID-19 pandemic, including, but not limited to, those described in Item 1A "Risk Factors" of the Form 10-K;
the extent and timing of costs and legal requirements related to CCR;
current and future litigation or regulatory investigations, proceedings, or inquiries, including litigation and other disputes related to the Kemper County energy facility;
the effects, extent, and timing of the entry of additional competition in the markets in which Southern Company's subsidiaries operate, including from the development and deployment of alternative energy sources;
variations in demand for electricity and natural gas;
available sources and costs of natural gas and other fuels;
the ability to complete necessary or desirable pipeline expansion or infrastructure projects, limits on pipeline capacity, and operational interruptions to natural gas distribution and transmission activities;
transmission constraints;
effects of inflation;
the ability to control costs and avoid cost and schedule overruns during the development, construction, and operation of facilities or other projects, including Plant Vogtle Units 3 and 4 (which includes components based on new technology that only within the last few years began initial operation in the global nuclear industry at this scale) and Plant Barry Unit 8, due to current and future challenges which include, but are not limited to, changes in labor costs, availability, and productivity; challenges with management of contractors or vendors; subcontractor performance; adverse weather conditions; shortages, delays, increased costs, or inconsistent quality of equipment, materials, and labor; contractor or supplier delay; delays due to judicial or regulatory action; nonperformance under construction, operating, or other agreements; operational readiness, including specialized operator training and required site safety programs; engineering or design problems; design and other licensing-based compliance matters, including, for nuclear units, inspections and the timely submittal by Southern Nuclear of the ITAAC documentation for each unit and the related reviews and approvals by the NRC necessary to support NRC authorization to load fuel; challenges with start-up activities, including major equipment failure, or system integration; and/or operational performance; and challenges related to the COVID-19 pandemic;
the ability to overcome or mitigate the current challenges at Plant Vogtle Units 3 and 4, as described in Note (B) to the Condensed Financial Statements under "Georgia Power – Nuclear Construction" in Item 1 herein, that could further impact the cost and schedule for the project;
legal proceedings and regulatory approvals and actions related to construction projects, such as Plant Vogtle Units 3 and 4, Plant Barry Unit 8, and pipeline projects, including PSC approvals and FERC and NRC actions;
under certain specified circumstances, a decision by holders of more than 10% of the ownership interests of Plant Vogtle Units 3 and 4 not to proceed with construction and the ability of other Vogtle Owners to tender a portion of their ownership interests to Georgia Power following certain construction cost increases;
8

    Table of Contents                                Index to Financial Statements
CAUTIONARY STATEMENT REGARDING FORWARD-LOOKING INFORMATION
(continued)
in the event Georgia Power becomes obligated to provide funding to MEAG Power with respect to the portion of MEAG Power's ownership interest in Plant Vogtle Units 3 and 4 involving JEA, any inability of Georgia Power to receive repayment of such funding;
the ability to construct facilities in accordance with the requirements of permits and licenses (including satisfaction of NRC requirements), to satisfy any environmental performance standards and the requirements of tax credits and other incentives, and to integrate facilities into the Southern Company system upon completion of construction;
investment performance of the employee and retiree benefit plans and nuclear decommissioning trust funds;
advances in technology, including the pace and extent of development of low- to no-carbon energy technologies and negative carbon concepts;
performance of counterparties under ongoing renewable energy partnerships and development agreements;
state and federal rate regulations and the impact of pending and future rate cases and negotiations, including rate actions relating to ROE, equity ratios, additional generating capacity, and fuel and other cost recovery mechanisms;
the ability to successfully operate the electric utilities' generating, transmission, and distribution facilities and Southern Company Gas' natural gas distribution and storage facilities and the successful performance of necessary corporate functions;
the inherent risks involved in operating and constructing nuclear generating facilities;
the inherent risks involved in transporting and storing natural gas;
the performance of projects undertaken by the non-utility businesses and the success of efforts to invest in and develop new opportunities;
internal restructuring or other restructuring options that may be pursued;
potential business strategies, including acquisitions or dispositions of assets or businesses, which cannot be assured to be completed or beneficial to Southern Company or its subsidiaries;
the ability of counterparties of Southern Company and its subsidiaries to make payments as and when due and to perform as required;
the ability to obtain new short- and long-term contracts with wholesale customers;
the direct or indirect effect on the Southern Company system's business resulting from cyber intrusion or physical attack and the threat of physical attacks;
interest rate fluctuations and financial market conditions and the results of financing efforts;
access to capital markets and other financing sources;
changes in Southern Company's and any of its subsidiaries' credit ratings;
changes in the method of determining LIBOR or the replacement of LIBOR with an alternative reference rate;
the ability of Southern Company's electric utilities to obtain additional generating capacity (or sell excess generating capacity) at competitive prices;
catastrophic events such as fires, earthquakes, explosions, floods, tornadoes, hurricanes and other storms, droughts, pandemic health events, political unrest, or other similar occurrences;
the direct or indirect effects on the Southern Company system's business resulting from incidents affecting the U.S. electric grid, natural gas pipeline infrastructure, or operation of generating or storage resources;
impairments of goodwill or long-lived assets;
the effect of accounting pronouncements issued periodically by standard-setting bodies; and
other factors discussed elsewhere herein and in other reports (including the Form 10-K) filed by the Registrants from time to time with the SEC.
The Registrants expressly disclaim any obligation to update any forward-looking statements.
9

    Table of Contents                                Index to Financial Statements
PART I
Item 1. Financial Statements (Unaudited).
 Page
10

    Table of Contents                                Index to Financial Statements

THE SOUTHERN COMPANY AND SUBSIDIARY COMPANIES
CONDENSED CONSOLIDATED STATEMENTS OF INCOME (UNAUDITED)
 
 For the Three Months Ended March 31,
 20212020
 (in millions)
Operating Revenues:
Retail electric revenues$3,342 $3,078 
Wholesale electric revenues545 418 
Other electric revenues170 151 
Natural gas revenues (includes alternative revenue programs of $2 and $9, respectively)
1,694 1,249 
Other revenues159 122 
Total operating revenues5,910 5,018 
Operating Expenses:
Fuel848