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Income Taxes - Deferred Tax Assets and Liabilities (Details) (USD $)
Dec. 31, 2014
Dec. 31, 2013
Deferred tax liabilities -    
Total - deferred tax liabilities $ 11,064,000,000us-gaap_DeferredTaxLiabilities $ 10,420,000,000us-gaap_DeferredTaxLiabilities
Deferred Tax Liabilities, Gross 16,256,000,000us-gaap_DeferredIncomeTaxLiabilities 13,995,000,000us-gaap_DeferredIncomeTaxLiabilities
Deferred tax assets -    
Total - deferred tax assets 5,241,000,000us-gaap_DeferredTaxAssetsGross 3,624,000,000us-gaap_DeferredTaxAssetsGross
Total deferred tax liabilities, net 5,192,000,000us-gaap_DeferredTaxAssetsLiabilitiesNet 3,575,000,000us-gaap_DeferredTaxAssetsLiabilitiesNet
Portion included in current assets/(liabilities), net 504,000,000so_PortionIncludedInCurrentTaxLiabilitiesCurrentTaxAssetsNet 143,000,000so_PortionIncludedInCurrentTaxLiabilitiesCurrentTaxAssetsNet
Valuation allowance (49,000,000)us-gaap_DeferredTaxAssetsValuationAllowance (49,000,000)us-gaap_DeferredTaxAssetsValuationAllowance
Accumulated deferred income taxes 11,568,000,000us-gaap_DeferredTaxLiabilitiesNoncurrent 10,563,000,000us-gaap_DeferredTaxLiabilitiesNoncurrent
Deferred State Tax Assets [Member]    
Deferred tax assets -    
Total - deferred tax assets 117,000,000us-gaap_DeferredTaxAssetsGross
/ us-gaap_RegulatoryAssetAxis
= so_DeferredStateTaxAssetsMember		 77,000,000us-gaap_DeferredTaxAssetsGross
/ us-gaap_RegulatoryAssetAxis
= so_DeferredStateTaxAssetsMember
Asset retirement obligations-asset [Member]    
Deferred tax assets -    
Total - deferred tax assets 871,000,000us-gaap_DeferredTaxAssetsGross
/ us-gaap_RegulatoryAssetAxis
= us-gaap_AssetRetirementObligationCostsMember		 824,000,000us-gaap_DeferredTaxAssetsGross
/ us-gaap_RegulatoryAssetAxis
= us-gaap_AssetRetirementObligationCostsMember
Kemper IGCC Loss [Member]    
Deferred tax assets -    
Total - deferred tax assets 631,000,000us-gaap_DeferredTaxAssetsGross
/ us-gaap_RegulatoryAssetAxis
= so_KemperIGCCLossMember		 472,000,000us-gaap_DeferredTaxAssetsGross
/ us-gaap_RegulatoryAssetAxis
= so_KemperIGCCLossMember
Unbilled revenues [Member]    
Deferred tax assets -    
Total - deferred tax assets 67,000,000us-gaap_DeferredTaxAssetsGross
/ us-gaap_AccountsNotesLoansAndFinancingReceivablesByBillingStatusTypeAxis
= us-gaap_UnbilledRevenuesMember		 116,000,000us-gaap_DeferredTaxAssetsGross
/ us-gaap_AccountsNotesLoansAndFinancingReceivablesByBillingStatusTypeAxis
= us-gaap_UnbilledRevenuesMember
Accelerated depreciation [Member]    
Deferred tax liabilities -    
Deferred Tax Liabilities, Gross 11,125,000,000us-gaap_DeferredIncomeTaxLiabilities
/ so_DeferredTaxAssetsLiabilitiesAxis
= so_AcceleratedDepreciationMember		 9,710,000,000us-gaap_DeferredIncomeTaxLiabilities
/ so_DeferredTaxAssetsLiabilitiesAxis
= so_AcceleratedDepreciationMember
Property basis differences [Member]    
Deferred tax liabilities -    
Deferred Tax Liabilities, Gross 1,332,000,000us-gaap_DeferredIncomeTaxLiabilities
/ so_DeferredTaxAssetsLiabilitiesAxis
= so_PropertyBasisDifferencesMember		 1,515,000,000us-gaap_DeferredIncomeTaxLiabilities
/ so_DeferredTaxAssetsLiabilitiesAxis
= so_PropertyBasisDifferencesMember
Leveraged lease basis differences [Member]    
Deferred tax liabilities -    
Deferred Tax Liabilities, Gross 299,000,000us-gaap_DeferredIncomeTaxLiabilities
/ so_DeferredTaxAssetsLiabilitiesAxis
= so_LeveragedLeaseBasisDifferencesMember		 287,000,000us-gaap_DeferredIncomeTaxLiabilities
/ so_DeferredTaxAssetsLiabilitiesAxis
= so_LeveragedLeaseBasisDifferencesMember
Employee benefit obligations [Member]    
Deferred tax liabilities -    
Deferred Tax Liabilities, Gross 613,000,000us-gaap_DeferredIncomeTaxLiabilities
/ so_DeferredTaxAssetsLiabilitiesAxis
= so_EmployeeBenefitObligationsMember		 491,000,000us-gaap_DeferredIncomeTaxLiabilities
/ so_DeferredTaxAssetsLiabilitiesAxis
= so_EmployeeBenefitObligationsMember
Deferred tax assets -    
Total - deferred tax assets 1,675,000,000us-gaap_DeferredTaxAssetsGross
/ so_DeferredTaxAssetsLiabilitiesAxis
= so_EmployeeBenefitObligationsMember		 1,048,000,000us-gaap_DeferredTaxAssetsGross
/ so_DeferredTaxAssetsLiabilitiesAxis
= so_EmployeeBenefitObligationsMember
Regulatory assets associated with employee benefit obligations [Member]    
Deferred tax liabilities -    
Deferred Tax Liabilities, Gross 1,390,000,000us-gaap_DeferredIncomeTaxLiabilities
/ so_DeferredTaxAssetsLiabilitiesAxis
= so_RegulatoryAssetsAssociatedWithEmployeeBenefitObligationsMember		 705,000,000us-gaap_DeferredIncomeTaxLiabilities
/ so_DeferredTaxAssetsLiabilitiesAxis
= so_RegulatoryAssetsAssociatedWithEmployeeBenefitObligationsMember
Premium on reacquired debt [Member]    
Deferred tax liabilities -    
Deferred Tax Liabilities, Gross 103,000,000us-gaap_DeferredIncomeTaxLiabilities
/ so_DeferredTaxAssetsLiabilitiesAxis
= so_PremiumOnReacquiredDebtMember		 113,000,000us-gaap_DeferredIncomeTaxLiabilities
/ so_DeferredTaxAssetsLiabilitiesAxis
= so_PremiumOnReacquiredDebtMember
Regulatory assets associated with asset retirement obligations [Member]    
Deferred tax liabilities -    
Deferred Tax Liabilities, Gross 871,000,000us-gaap_DeferredIncomeTaxLiabilities
/ so_DeferredTaxAssetsLiabilitiesAxis
= so_RegulatoryAssetsAssociatedWithAssetRetirementObligationsMember		 824,000,000us-gaap_DeferredIncomeTaxLiabilities
/ so_DeferredTaxAssetsLiabilitiesAxis
= so_RegulatoryAssetsAssociatedWithAssetRetirementObligationsMember
Federal effect of state deferred taxes [Member]    
Deferred tax assets -    
Total - deferred tax assets 430,000,000us-gaap_DeferredTaxAssetsGross
/ so_DeferredTaxAssetsLiabilitiesAxis
= so_FederalEffectOfStateDeferredTaxesMember		 421,000,000us-gaap_DeferredTaxAssetsGross
/ so_DeferredTaxAssetsLiabilitiesAxis
= so_FederalEffectOfStateDeferredTaxesMember
Other deferred tax liabilities [Member]    
Deferred tax liabilities -    
Deferred Tax Liabilities, Gross 523,000,000us-gaap_DeferredIncomeTaxLiabilities
/ so_DeferredTaxAssetsLiabilitiesAxis
= so_OtherDeferredTaxLiabilitiesMember		 350,000,000us-gaap_DeferredIncomeTaxLiabilities
/ so_DeferredTaxAssetsLiabilitiesAxis
= so_OtherDeferredTaxLiabilitiesMember
Over recovered fuel clause [Member]    
Deferred tax assets -    
Total - deferred tax assets 0us-gaap_DeferredTaxAssetsGross
/ so_DeferredTaxAssetsLiabilitiesAxis
= so_OverRecoveredFuelClauseMember		 30,000,000us-gaap_DeferredTaxAssetsGross
/ so_DeferredTaxAssetsLiabilitiesAxis
= so_OverRecoveredFuelClauseMember
Other property basis differences [Member]    
Deferred tax assets -    
Total - deferred tax assets 453,000,000us-gaap_DeferredTaxAssetsGross
/ so_DeferredTaxAssetsLiabilitiesAxis
= so_OtherPropertyBasisDifferencesMember		 157,000,000us-gaap_DeferredTaxAssetsGross
/ so_DeferredTaxAssetsLiabilitiesAxis
= so_OtherPropertyBasisDifferencesMember
Deferred costs [Member]    
Deferred tax assets -    
Total - deferred tax assets 86,000,000us-gaap_DeferredTaxAssetsGross
/ so_DeferredTaxAssetsLiabilitiesAxis
= so_DeferredCostsMember		 84,000,000us-gaap_DeferredTaxAssetsGross
/ so_DeferredTaxAssetsLiabilitiesAxis
= so_DeferredCostsMember
Tax credit carryforward [Member]    
Deferred tax assets -    
Total - deferred tax assets 480,000,000us-gaap_DeferredTaxAssetsGross
/ so_DeferredTaxAssetsLiabilitiesAxis
= so_TaxCreditCarryforwardMember		 121,000,000us-gaap_DeferredTaxAssetsGross
/ so_DeferredTaxAssetsLiabilitiesAxis
= so_TaxCreditCarryforwardMember
Other Comprehensive Income Losses [Member]    
Deferred tax assets -    
Total - deferred tax assets 89,000,000us-gaap_DeferredTaxAssetsGross
/ so_DeferredTaxAssetsLiabilitiesAxis
= so_OtherComprehensiveIncomeLossesMember		 54,000,000us-gaap_DeferredTaxAssetsGross
/ so_DeferredTaxAssetsLiabilitiesAxis
= so_OtherComprehensiveIncomeLossesMember
Other deferred tax assets [Member]    
Deferred tax assets -    
Total - deferred tax assets 342,000,000us-gaap_DeferredTaxAssetsGross
/ so_DeferredTaxAssetsLiabilitiesAxis
= so_OtherDeferredTaxAssetsMember		 220,000,000us-gaap_DeferredTaxAssetsGross
/ so_DeferredTaxAssetsLiabilitiesAxis
= so_OtherDeferredTaxAssetsMember
Alabama Power [Member]    
Deferred tax liabilities -    
Total - deferred tax liabilities 3,856,000,000us-gaap_DeferredTaxLiabilities
/ dei_LegalEntityAxis
= so_AlabamaPowerMember		 3,578,000,000us-gaap_DeferredTaxLiabilities
/ dei_LegalEntityAxis
= so_AlabamaPowerMember
Deferred Tax Liabilities, Gross 4,997,000,000us-gaap_DeferredIncomeTaxLiabilities
/ dei_LegalEntityAxis
= so_AlabamaPowerMember		 4,516,000,000us-gaap_DeferredIncomeTaxLiabilities
/ dei_LegalEntityAxis
= so_AlabamaPowerMember
Deferred tax assets -    
Total - deferred tax assets 1,141,000,000us-gaap_DeferredTaxAssetsGross
/ dei_LegalEntityAxis
= so_AlabamaPowerMember		 938,000,000us-gaap_DeferredTaxAssetsGross
/ dei_LegalEntityAxis
= so_AlabamaPowerMember
Portion included in current assets/(liabilities), net 18,000,000so_PortionIncludedInCurrentTaxLiabilitiesCurrentTaxAssetsNet
/ dei_LegalEntityAxis
= so_AlabamaPowerMember		 25,000,000so_PortionIncludedInCurrentTaxLiabilitiesCurrentTaxAssetsNet
/ dei_LegalEntityAxis
= so_AlabamaPowerMember
Accumulated deferred income taxes 3,874,000,000us-gaap_DeferredTaxLiabilitiesNoncurrent
/ dei_LegalEntityAxis
= so_AlabamaPowerMember		 3,603,000,000us-gaap_DeferredTaxLiabilitiesNoncurrent
/ dei_LegalEntityAxis
= so_AlabamaPowerMember
Alabama Power [Member] | Accelerated depreciation [Member]    
Deferred tax liabilities -    
Deferred Tax Liabilities, Gross 3,429,000,000us-gaap_DeferredIncomeTaxLiabilities
/ so_DeferredTaxAssetsLiabilitiesAxis
= so_AcceleratedDepreciationMember
/ dei_LegalEntityAxis
= so_AlabamaPowerMember		 3,187,000,000us-gaap_DeferredIncomeTaxLiabilities
/ so_DeferredTaxAssetsLiabilitiesAxis
= so_AcceleratedDepreciationMember
/ dei_LegalEntityAxis
= so_AlabamaPowerMember
Alabama Power [Member] | Property basis differences [Member]    
Deferred tax liabilities -    
Deferred Tax Liabilities, Gross 457,000,000us-gaap_DeferredIncomeTaxLiabilities
/ so_DeferredTaxAssetsLiabilitiesAxis
= so_PropertyBasisDifferencesMember
/ dei_LegalEntityAxis
= so_AlabamaPowerMember		 458,000,000us-gaap_DeferredIncomeTaxLiabilities
/ so_DeferredTaxAssetsLiabilitiesAxis
= so_PropertyBasisDifferencesMember
/ dei_LegalEntityAxis
= so_AlabamaPowerMember
Alabama Power [Member] | Leveraged lease basis differences [Member]    
Deferred tax liabilities -    
Deferred Tax Liabilities, Gross 30,000,000us-gaap_DeferredIncomeTaxLiabilities
/ so_DeferredTaxAssetsLiabilitiesAxis
= so_LeveragedLeaseBasisDifferencesMember
/ dei_LegalEntityAxis
= so_AlabamaPowerMember		 33,000,000us-gaap_DeferredIncomeTaxLiabilities
/ so_DeferredTaxAssetsLiabilitiesAxis
= so_LeveragedLeaseBasisDifferencesMember
/ dei_LegalEntityAxis
= so_AlabamaPowerMember
Alabama Power [Member] | Employee benefit obligations [Member]    
Deferred tax liabilities -    
Deferred Tax Liabilities, Gross 215,000,000us-gaap_DeferredIncomeTaxLiabilities
/ so_DeferredTaxAssetsLiabilitiesAxis
= so_EmployeeBenefitObligationsMember
/ dei_LegalEntityAxis
= so_AlabamaPowerMember		 209,000,000us-gaap_DeferredIncomeTaxLiabilities
/ so_DeferredTaxAssetsLiabilitiesAxis
= so_EmployeeBenefitObligationsMember
/ dei_LegalEntityAxis
= so_AlabamaPowerMember
Deferred tax assets -    
Total - deferred tax assets 400,000,000us-gaap_DeferredTaxAssetsGross
/ so_DeferredTaxAssetsLiabilitiesAxis
= so_EmployeeBenefitObligationsMember
/ dei_LegalEntityAxis
= so_AlabamaPowerMember		 231,000,000us-gaap_DeferredTaxAssetsGross
/ so_DeferredTaxAssetsLiabilitiesAxis
= so_EmployeeBenefitObligationsMember
/ dei_LegalEntityAxis
= so_AlabamaPowerMember
Alabama Power [Member] | Regulatory assets associated with employee benefit obligations [Member]    
Deferred tax liabilities -    
Deferred Tax Liabilities, Gross 366,000,000us-gaap_DeferredIncomeTaxLiabilities
/ so_DeferredTaxAssetsLiabilitiesAxis
= so_RegulatoryAssetsAssociatedWithEmployeeBenefitObligationsMember
/ dei_LegalEntityAxis
= so_AlabamaPowerMember		 198,000,000us-gaap_DeferredIncomeTaxLiabilities
/ so_DeferredTaxAssetsLiabilitiesAxis
= so_RegulatoryAssetsAssociatedWithEmployeeBenefitObligationsMember
/ dei_LegalEntityAxis
= so_AlabamaPowerMember
Alabama Power [Member] | Asset retirement obligation [Member]    
Deferred tax liabilities -    
Deferred Tax Liabilities, Gross 59,000,000us-gaap_DeferredIncomeTaxLiabilities
/ so_DeferredTaxAssetsLiabilitiesAxis
= so_AssetRetirementObligationLiabilityMember
/ dei_LegalEntityAxis
= so_AlabamaPowerMember		 38,000,000us-gaap_DeferredIncomeTaxLiabilities
/ so_DeferredTaxAssetsLiabilitiesAxis
= so_AssetRetirementObligationLiabilityMember
/ dei_LegalEntityAxis
= so_AlabamaPowerMember
Deferred tax assets -    
Total - deferred tax assets 344,000,000us-gaap_DeferredTaxAssetsGross
/ so_DeferredTaxAssetsLiabilitiesAxis
= so_AssetRetirementObligationLiabilityMember
/ dei_LegalEntityAxis
= so_AlabamaPowerMember		 303,000,000us-gaap_DeferredTaxAssetsGross
/ so_DeferredTaxAssetsLiabilitiesAxis
= so_AssetRetirementObligationLiabilityMember
/ dei_LegalEntityAxis
= so_AlabamaPowerMember
Alabama Power [Member] | Regulatory assets associated with asset retirement obligations [Member]    
Deferred tax liabilities -    
Deferred Tax Liabilities, Gross 285,000,000us-gaap_DeferredIncomeTaxLiabilities
/ so_DeferredTaxAssetsLiabilitiesAxis
= so_RegulatoryAssetsAssociatedWithAssetRetirementObligationsMember
/ dei_LegalEntityAxis
= so_AlabamaPowerMember		 265,000,000us-gaap_DeferredIncomeTaxLiabilities
/ so_DeferredTaxAssetsLiabilitiesAxis
= so_RegulatoryAssetsAssociatedWithAssetRetirementObligationsMember
/ dei_LegalEntityAxis
= so_AlabamaPowerMember
Alabama Power [Member] | Federal effect of state deferred taxes [Member]    
Deferred tax assets -    
Total - deferred tax assets 219,000,000us-gaap_DeferredTaxAssetsGross
/ so_DeferredTaxAssetsLiabilitiesAxis
= so_FederalEffectOfStateDeferredTaxesMember
/ dei_LegalEntityAxis
= so_AlabamaPowerMember		 205,000,000us-gaap_DeferredTaxAssetsGross
/ so_DeferredTaxAssetsLiabilitiesAxis
= so_FederalEffectOfStateDeferredTaxesMember
/ dei_LegalEntityAxis
= so_AlabamaPowerMember
Alabama Power [Member] | Other deferred tax liabilities [Member]    
Deferred tax liabilities -    
Deferred Tax Liabilities, Gross 156,000,000us-gaap_DeferredIncomeTaxLiabilities
/ so_DeferredTaxAssetsLiabilitiesAxis
= so_OtherDeferredTaxLiabilitiesMember
/ dei_LegalEntityAxis
= so_AlabamaPowerMember		 128,000,000us-gaap_DeferredIncomeTaxLiabilities
/ so_DeferredTaxAssetsLiabilitiesAxis
= so_OtherDeferredTaxLiabilitiesMember
/ dei_LegalEntityAxis
= so_AlabamaPowerMember
Alabama Power [Member] | Unbilled revenues [Member]    
Deferred tax assets -    
Total - deferred tax assets 42,000,000us-gaap_DeferredTaxAssetsGross
/ so_DeferredTaxAssetsLiabilitiesAxis
= us-gaap_UnbilledRevenuesMember
/ dei_LegalEntityAxis
= so_AlabamaPowerMember		 41,000,000us-gaap_DeferredTaxAssetsGross
/ so_DeferredTaxAssetsLiabilitiesAxis
= us-gaap_UnbilledRevenuesMember
/ dei_LegalEntityAxis
= so_AlabamaPowerMember
Alabama Power [Member] | Storm Reserve [Member]    
Deferred tax assets -    
Total - deferred tax assets 27,000,000us-gaap_DeferredTaxAssetsGross
/ so_DeferredTaxAssetsLiabilitiesAxis
= so_StormReserveMember
/ dei_LegalEntityAxis
= so_AlabamaPowerMember		 32,000,000us-gaap_DeferredTaxAssetsGross
/ so_DeferredTaxAssetsLiabilitiesAxis
= so_StormReserveMember
/ dei_LegalEntityAxis
= so_AlabamaPowerMember
Alabama Power [Member] | Other Comprehensive Income Losses [Member]    
Deferred tax assets -    
Total - deferred tax assets 19,000,000us-gaap_DeferredTaxAssetsGross
/ so_DeferredTaxAssetsLiabilitiesAxis
= so_OtherComprehensiveIncomeLossesMember
/ dei_LegalEntityAxis
= so_AlabamaPowerMember		 18,000,000us-gaap_DeferredTaxAssetsGross
/ so_DeferredTaxAssetsLiabilitiesAxis
= so_OtherComprehensiveIncomeLossesMember
/ dei_LegalEntityAxis
= so_AlabamaPowerMember
Alabama Power [Member] | Other deferred tax assets [Member]    
Deferred tax assets -    
Total - deferred tax assets 90,000,000us-gaap_DeferredTaxAssetsGross
/ so_DeferredTaxAssetsLiabilitiesAxis
= so_OtherDeferredTaxAssetsMember
/ dei_LegalEntityAxis
= so_AlabamaPowerMember		 108,000,000us-gaap_DeferredTaxAssetsGross
/ so_DeferredTaxAssetsLiabilitiesAxis
= so_OtherDeferredTaxAssetsMember
/ dei_LegalEntityAxis
= so_AlabamaPowerMember
Georgia Power [Member]    
Deferred tax liabilities -    
Total - deferred tax liabilities 5,473,000,000us-gaap_DeferredTaxLiabilities
/ dei_LegalEntityAxis
= so_GeorgiaPowerMember		 5,132,000,000us-gaap_DeferredTaxLiabilities
/ dei_LegalEntityAxis
= so_GeorgiaPowerMember
Deferred Tax Liabilities, Gross 7,210,000,000us-gaap_DeferredIncomeTaxLiabilities
/ dei_LegalEntityAxis
= so_GeorgiaPowerMember		 6,596,000,000us-gaap_DeferredIncomeTaxLiabilities
/ dei_LegalEntityAxis
= so_GeorgiaPowerMember
Deferred tax assets -    
Total - deferred tax assets 1,737,000,000us-gaap_DeferredTaxAssetsGross
/ dei_LegalEntityAxis
= so_GeorgiaPowerMember		 1,464,000,000us-gaap_DeferredTaxAssetsGross
/ dei_LegalEntityAxis
= so_GeorgiaPowerMember
Portion included in current assets/(liabilities), net 34,000,000so_PortionIncludedInCurrentTaxLiabilitiesCurrentTaxAssetsNet
/ dei_LegalEntityAxis
= so_GeorgiaPowerMember		 68,000,000so_PortionIncludedInCurrentTaxLiabilitiesCurrentTaxAssetsNet
/ dei_LegalEntityAxis
= so_GeorgiaPowerMember
Accumulated deferred income taxes 5,507,000,000us-gaap_DeferredTaxLiabilitiesNoncurrent
/ dei_LegalEntityAxis
= so_GeorgiaPowerMember		 5,200,000,000us-gaap_DeferredTaxLiabilitiesNoncurrent
/ dei_LegalEntityAxis
= so_GeorgiaPowerMember
Georgia Power [Member] | Accelerated depreciation [Member]    
Deferred tax liabilities -    
Deferred Tax Liabilities, Gross 4,732,000,000us-gaap_DeferredIncomeTaxLiabilities
/ so_DeferredTaxAssetsLiabilitiesAxis
= so_AcceleratedDepreciationMember
/ dei_LegalEntityAxis
= so_GeorgiaPowerMember		 4,479,000,000us-gaap_DeferredIncomeTaxLiabilities
/ so_DeferredTaxAssetsLiabilitiesAxis
= so_AcceleratedDepreciationMember
/ dei_LegalEntityAxis
= so_GeorgiaPowerMember
Georgia Power [Member] | Property basis differences [Member]    
Deferred tax liabilities -    
Deferred Tax Liabilities, Gross 811,000,000us-gaap_DeferredIncomeTaxLiabilities
/ so_DeferredTaxAssetsLiabilitiesAxis
= so_PropertyBasisDifferencesMember
/ dei_LegalEntityAxis
= so_GeorgiaPowerMember		 873,000,000us-gaap_DeferredIncomeTaxLiabilities
/ so_DeferredTaxAssetsLiabilitiesAxis
= so_PropertyBasisDifferencesMember
/ dei_LegalEntityAxis
= so_GeorgiaPowerMember
Georgia Power [Member] | Employee benefit obligations [Member]    
Deferred tax liabilities -    
Deferred Tax Liabilities, Gross 329,000,000us-gaap_DeferredIncomeTaxLiabilities
/ so_DeferredTaxAssetsLiabilitiesAxis
= so_EmployeeBenefitObligationsMember
/ dei_LegalEntityAxis
= so_GeorgiaPowerMember		 232,000,000us-gaap_DeferredIncomeTaxLiabilities
/ so_DeferredTaxAssetsLiabilitiesAxis
= so_EmployeeBenefitObligationsMember
/ dei_LegalEntityAxis
= so_GeorgiaPowerMember
Deferred tax assets -    
Total - deferred tax assets 642,000,000us-gaap_DeferredTaxAssetsGross
/ so_DeferredTaxAssetsLiabilitiesAxis
= so_EmployeeBenefitObligationsMember
/ dei_LegalEntityAxis
= so_GeorgiaPowerMember		 388,000,000us-gaap_DeferredTaxAssetsGross
/ so_DeferredTaxAssetsLiabilitiesAxis
= so_EmployeeBenefitObligationsMember
/ dei_LegalEntityAxis
= so_GeorgiaPowerMember
Georgia Power [Member] | Regulatory assets associated with employee benefit obligations [Member]    
Deferred tax liabilities -    
Deferred Tax Liabilities, Gross 534,000,000us-gaap_DeferredIncomeTaxLiabilities
/ so_DeferredTaxAssetsLiabilitiesAxis
= so_RegulatoryAssetsAssociatedWithEmployeeBenefitObligationsMember
/ dei_LegalEntityAxis
= so_GeorgiaPowerMember		 276,000,000us-gaap_DeferredIncomeTaxLiabilities
/ so_DeferredTaxAssetsLiabilitiesAxis
= so_RegulatoryAssetsAssociatedWithEmployeeBenefitObligationsMember
/ dei_LegalEntityAxis
= so_GeorgiaPowerMember
Georgia Power [Member] | Premium on reacquired debt [Member]    
Deferred tax liabilities -    
Deferred Tax Liabilities, Gross 66,000,000us-gaap_DeferredIncomeTaxLiabilities
/ so_DeferredTaxAssetsLiabilitiesAxis
= so_PremiumOnReacquiredDebtMember
/ dei_LegalEntityAxis
= so_GeorgiaPowerMember		 73,000,000us-gaap_DeferredIncomeTaxLiabilities
/ so_DeferredTaxAssetsLiabilitiesAxis
= so_PremiumOnReacquiredDebtMember
/ dei_LegalEntityAxis
= so_GeorgiaPowerMember
Georgia Power [Member] | Under recovered fuel clause [Member]    
Deferred tax liabilities -    
Deferred Tax Liabilities, Gross 81,000,000us-gaap_DeferredIncomeTaxLiabilities
/ so_DeferredTaxAssetsLiabilitiesAxis
= so_UnderRecoveredFuelClauseMember
/ dei_LegalEntityAxis
= so_GeorgiaPowerMember		 0us-gaap_DeferredIncomeTaxLiabilities
/ so_DeferredTaxAssetsLiabilitiesAxis
= so_UnderRecoveredFuelClauseMember
/ dei_LegalEntityAxis
= so_GeorgiaPowerMember
Georgia Power [Member] | Regulatory assets associated with asset retirement obligations [Member]    
Deferred tax liabilities -    
Deferred Tax Liabilities, Gross 497,000,000us-gaap_DeferredIncomeTaxLiabilities
/ so_DeferredTaxAssetsLiabilitiesAxis
= so_RegulatoryAssetsAssociatedWithAssetRetirementObligationsMember
/ dei_LegalEntityAxis
= so_GeorgiaPowerMember		 495,000,000us-gaap_DeferredIncomeTaxLiabilities
/ so_DeferredTaxAssetsLiabilitiesAxis
= so_RegulatoryAssetsAssociatedWithAssetRetirementObligationsMember
/ dei_LegalEntityAxis
= so_GeorgiaPowerMember
Deferred tax assets -    
Total - deferred tax assets 497,000,000us-gaap_DeferredTaxAssetsGross
/ so_DeferredTaxAssetsLiabilitiesAxis
= so_RegulatoryAssetsAssociatedWithAssetRetirementObligationsMember
/ dei_LegalEntityAxis
= so_GeorgiaPowerMember		 495,000,000us-gaap_DeferredTaxAssetsGross
/ so_DeferredTaxAssetsLiabilitiesAxis
= so_RegulatoryAssetsAssociatedWithAssetRetirementObligationsMember
/ dei_LegalEntityAxis
= so_GeorgiaPowerMember
Georgia Power [Member] | Federal effect of state deferred taxes [Member]    
Deferred tax assets -    
Total - deferred tax assets 148,000,000us-gaap_DeferredTaxAssetsGross
/ so_DeferredTaxAssetsLiabilitiesAxis
= so_FederalEffectOfStateDeferredTaxesMember
/ dei_LegalEntityAxis
= so_GeorgiaPowerMember		 159,000,000us-gaap_DeferredTaxAssetsGross
/ so_DeferredTaxAssetsLiabilitiesAxis
= so_FederalEffectOfStateDeferredTaxesMember
/ dei_LegalEntityAxis
= so_GeorgiaPowerMember
Georgia Power [Member] | Other deferred tax liabilities [Member]    
Deferred tax liabilities -    
Deferred Tax Liabilities, Gross 160,000,000us-gaap_DeferredIncomeTaxLiabilities
/ so_DeferredTaxAssetsLiabilitiesAxis
= so_OtherDeferredTaxLiabilitiesMember
/ dei_LegalEntityAxis
= so_GeorgiaPowerMember		 168,000,000us-gaap_DeferredIncomeTaxLiabilities
/ so_DeferredTaxAssetsLiabilitiesAxis
= so_OtherDeferredTaxLiabilitiesMember
/ dei_LegalEntityAxis
= so_GeorgiaPowerMember
Georgia Power [Member] | Unbilled revenues [Member]    
Deferred tax assets -    
Total - deferred tax assets 46,000,000us-gaap_DeferredTaxAssetsGross
/ so_DeferredTaxAssetsLiabilitiesAxis
= us-gaap_UnbilledRevenuesMember
/ dei_LegalEntityAxis
= so_GeorgiaPowerMember		 53,000,000us-gaap_DeferredTaxAssetsGross
/ so_DeferredTaxAssetsLiabilitiesAxis
= us-gaap_UnbilledRevenuesMember
/ dei_LegalEntityAxis
= so_GeorgiaPowerMember
Georgia Power [Member] | Over recovered fuel clause [Member]    
Deferred tax assets -    
Total - deferred tax assets 0us-gaap_DeferredTaxAssetsGross
/ so_DeferredTaxAssetsLiabilitiesAxis
= so_OverRecoveredFuelClauseMember
/ dei_LegalEntityAxis
= so_GeorgiaPowerMember		 22,000,000us-gaap_DeferredTaxAssetsGross
/ so_DeferredTaxAssetsLiabilitiesAxis
= so_OverRecoveredFuelClauseMember
/ dei_LegalEntityAxis
= so_GeorgiaPowerMember
Georgia Power [Member] | Other property basis differences [Member]    
Deferred tax assets -    
Total - deferred tax assets 86,000,000us-gaap_DeferredTaxAssetsGross
/ so_DeferredTaxAssetsLiabilitiesAxis
= so_OtherPropertyBasisDifferencesMember
/ dei_LegalEntityAxis
= so_GeorgiaPowerMember		 93,000,000us-gaap_DeferredTaxAssetsGross
/ so_DeferredTaxAssetsLiabilitiesAxis
= so_OtherPropertyBasisDifferencesMember
/ dei_LegalEntityAxis
= so_GeorgiaPowerMember
Georgia Power [Member] | Deferred costs [Member]    
Deferred tax assets -    
Total - deferred tax assets 86,000,000us-gaap_DeferredTaxAssetsGross
/ so_DeferredTaxAssetsLiabilitiesAxis
= so_DeferredCostsMember
/ dei_LegalEntityAxis
= so_GeorgiaPowerMember		 84,000,000us-gaap_DeferredTaxAssetsGross
/ so_DeferredTaxAssetsLiabilitiesAxis
= so_DeferredCostsMember
/ dei_LegalEntityAxis
= so_GeorgiaPowerMember
Georgia Power [Member] | Cost of removal [Member]    
Deferred tax assets -    
Total - deferred tax assets 11,000,000us-gaap_DeferredTaxAssetsGross
/ so_DeferredTaxAssetsLiabilitiesAxis
= so_CostOfRemovalMember
/ dei_LegalEntityAxis
= so_GeorgiaPowerMember		 17,000,000us-gaap_DeferredTaxAssetsGross
/ so_DeferredTaxAssetsLiabilitiesAxis
= so_CostOfRemovalMember
/ dei_LegalEntityAxis
= so_GeorgiaPowerMember
Georgia Power [Member] | Tax credit carryforward [Member]    
Deferred tax assets -    
Total - deferred tax assets 170,000,000us-gaap_DeferredTaxAssetsGross
/ so_DeferredTaxAssetsLiabilitiesAxis
= so_TaxCreditCarryforwardMember
/ dei_LegalEntityAxis
= so_GeorgiaPowerMember		 118,000,000us-gaap_DeferredTaxAssetsGross
/ so_DeferredTaxAssetsLiabilitiesAxis
= so_TaxCreditCarryforwardMember
/ dei_LegalEntityAxis
= so_GeorgiaPowerMember
Georgia Power [Member] | Federal Tax Credit Carryforward [Member]    
Deferred tax assets -    
Total - deferred tax assets 5,000,000us-gaap_DeferredTaxAssetsGross
/ so_DeferredTaxAssetsLiabilitiesAxis
= so_FederalTaxCreditCarryforwardMember
/ dei_LegalEntityAxis
= so_GeorgiaPowerMember		 3,000,000us-gaap_DeferredTaxAssetsGross
/ so_DeferredTaxAssetsLiabilitiesAxis
= so_FederalTaxCreditCarryforwardMember
/ dei_LegalEntityAxis
= so_GeorgiaPowerMember
Georgia Power [Member] | Other deferred tax assets [Member]    
Deferred tax assets -    
Total - deferred tax assets 46,000,000us-gaap_DeferredTaxAssetsGross
/ so_DeferredTaxAssetsLiabilitiesAxis
= so_OtherDeferredTaxAssetsMember
/ dei_LegalEntityAxis
= so_GeorgiaPowerMember		 32,000,000us-gaap_DeferredTaxAssetsGross
/ so_DeferredTaxAssetsLiabilitiesAxis
= so_OtherDeferredTaxAssetsMember
/ dei_LegalEntityAxis
= so_GeorgiaPowerMember
Gulf Power [Member]    
Deferred tax liabilities -    
Total - deferred tax liabilities 796,589,000us-gaap_DeferredTaxLiabilities
/ dei_LegalEntityAxis
= so_GulfPowerMember		 725,974,000us-gaap_DeferredTaxLiabilities
/ dei_LegalEntityAxis
= so_GulfPowerMember
Deferred Tax Liabilities, Gross 968,016,000us-gaap_DeferredIncomeTaxLiabilities
/ dei_LegalEntityAxis
= so_GulfPowerMember		 858,980,000us-gaap_DeferredIncomeTaxLiabilities
/ dei_LegalEntityAxis
= so_GulfPowerMember
Deferred tax assets -    
Total - deferred tax assets 171,427,000us-gaap_DeferredTaxAssetsGross
/ dei_LegalEntityAxis
= so_GulfPowerMember		 133,006,000us-gaap_DeferredTaxAssetsGross
/ dei_LegalEntityAxis
= so_GulfPowerMember
Portion included in current assets/(liabilities), net 3,134,000so_PortionIncludedInCurrentTaxLiabilitiesCurrentTaxAssetsNet
/ dei_LegalEntityAxis
= so_GulfPowerMember		 8,381,000so_PortionIncludedInCurrentTaxLiabilitiesCurrentTaxAssetsNet
/ dei_LegalEntityAxis
= so_GulfPowerMember
Accumulated deferred income taxes 799,723,000us-gaap_DeferredTaxLiabilitiesNoncurrent
/ dei_LegalEntityAxis
= so_GulfPowerMember		 734,355,000us-gaap_DeferredTaxLiabilitiesNoncurrent
/ dei_LegalEntityAxis
= so_GulfPowerMember
Gulf Power [Member] | Accelerated depreciation [Member]    
Deferred tax liabilities -    
Deferred Tax Liabilities, Gross 776,953,000us-gaap_DeferredIncomeTaxLiabilities
/ so_DeferredTaxAssetsLiabilitiesAxis
= so_AcceleratedDepreciationMember
/ dei_LegalEntityAxis
= so_GulfPowerMember		 721,087,000us-gaap_DeferredIncomeTaxLiabilities
/ so_DeferredTaxAssetsLiabilitiesAxis
= so_AcceleratedDepreciationMember
/ dei_LegalEntityAxis
= so_GulfPowerMember
Gulf Power [Member] | Property basis differences [Member]    
Deferred tax liabilities -    
Deferred Tax Liabilities, Gross 52,242,000us-gaap_DeferredIncomeTaxLiabilities
/ so_DeferredTaxAssetsLiabilitiesAxis
= so_PropertyBasisDifferencesMember
/ dei_LegalEntityAxis
= so_GulfPowerMember		 45,960,000us-gaap_DeferredIncomeTaxLiabilities
/ so_DeferredTaxAssetsLiabilitiesAxis
= so_PropertyBasisDifferencesMember
/ dei_LegalEntityAxis
= so_GulfPowerMember
Gulf Power [Member] | Employee benefit obligations [Member]    
Deferred tax liabilities -    
Deferred Tax Liabilities, Gross 34,405,000us-gaap_DeferredIncomeTaxLiabilities
/ so_DeferredTaxAssetsLiabilitiesAxis
= so_EmployeeBenefitObligationsMember
/ dei_LegalEntityAxis
= so_GulfPowerMember		 25,800,000us-gaap_DeferredIncomeTaxLiabilities
/ so_DeferredTaxAssetsLiabilitiesAxis
= so_EmployeeBenefitObligationsMember
/ dei_LegalEntityAxis
= so_GulfPowerMember
Gulf Power [Member] | Pension and other employee benefits [Member]    
Deferred tax assets -    
Total - deferred tax assets 65,506,000us-gaap_DeferredTaxAssetsGross
/ so_DeferredTaxAssetsLiabilitiesAxis
= so_PensionAndOtherEmployeeBenefitsMember
/ dei_LegalEntityAxis
= so_GulfPowerMember		 33,015,000us-gaap_DeferredTaxAssetsGross
/ so_DeferredTaxAssetsLiabilitiesAxis
= so_PensionAndOtherEmployeeBenefitsMember
/ dei_LegalEntityAxis
= so_GulfPowerMember
Gulf Power [Member] | Regulatory assets associated with employee benefit obligations [Member]    
Deferred tax liabilities -    
Deferred Tax Liabilities, Gross 59,788,000us-gaap_DeferredIncomeTaxLiabilities
/ so_DeferredTaxAssetsLiabilitiesAxis
= so_RegulatoryAssetsAssociatedWithEmployeeBenefitObligationsMember
/ dei_LegalEntityAxis
= so_GulfPowerMember		 27,660,000us-gaap_DeferredIncomeTaxLiabilities
/ so_DeferredTaxAssetsLiabilitiesAxis
= so_RegulatoryAssetsAssociatedWithEmployeeBenefitObligationsMember
/ dei_LegalEntityAxis
= so_GulfPowerMember
Gulf Power [Member] | Fuel Recovery Clause [Member]    
Deferred tax liabilities -    
Deferred Tax Liabilities, Gross 16,148,000us-gaap_DeferredIncomeTaxLiabilities
/ so_DeferredTaxAssetsLiabilitiesAxis
= so_FuelRecoveryClauseMember
/ dei_LegalEntityAxis
= so_GulfPowerMember		 7,972,000us-gaap_DeferredIncomeTaxLiabilities
/ so_DeferredTaxAssetsLiabilitiesAxis
= so_FuelRecoveryClauseMember
/ dei_LegalEntityAxis
= so_GulfPowerMember
Gulf Power [Member] | Asset retirement obligation [Member]    
Deferred tax assets -    
Total - deferred tax assets 6,768,000us-gaap_DeferredTaxAssetsGross
/ so_DeferredTaxAssetsLiabilitiesAxis
= so_AssetRetirementObligationLiabilityMember
/ dei_LegalEntityAxis
= so_GulfPowerMember		 6,554,000us-gaap_DeferredTaxAssetsGross
/ so_DeferredTaxAssetsLiabilitiesAxis
= so_AssetRetirementObligationLiabilityMember
/ dei_LegalEntityAxis
= so_GulfPowerMember
Gulf Power [Member] | Regulatory assets associated with asset retirement obligations [Member]    
Deferred tax liabilities -    
Deferred Tax Liabilities, Gross 6,768,000us-gaap_DeferredIncomeTaxLiabilities
/ so_DeferredTaxAssetsLiabilitiesAxis
= so_RegulatoryAssetsAssociatedWithAssetRetirementObligationsMember
/ dei_LegalEntityAxis
= so_GulfPowerMember		 6,554,000us-gaap_DeferredIncomeTaxLiabilities
/ so_DeferredTaxAssetsLiabilitiesAxis
= so_RegulatoryAssetsAssociatedWithAssetRetirementObligationsMember
/ dei_LegalEntityAxis
= so_GulfPowerMember
Gulf Power [Member] | Federal effect of state deferred taxes [Member]    
Deferred tax assets -    
Total - deferred tax assets 30,587,000us-gaap_DeferredTaxAssetsGross
/ so_DeferredTaxAssetsLiabilitiesAxis
= so_FederalEffectOfStateDeferredTaxesMember
/ dei_LegalEntityAxis
= so_GulfPowerMember		 24,277,000us-gaap_DeferredTaxAssetsGross
/ so_DeferredTaxAssetsLiabilitiesAxis
= so_FederalEffectOfStateDeferredTaxesMember
/ dei_LegalEntityAxis
= so_GulfPowerMember
Gulf Power [Member] | Other deferred tax liabilities [Member]    
Deferred tax liabilities -    
Deferred Tax Liabilities, Gross 21,712,000us-gaap_DeferredIncomeTaxLiabilities
/ so_DeferredTaxAssetsLiabilitiesAxis
= so_OtherDeferredTaxLiabilitiesMember
/ dei_LegalEntityAxis
= so_GulfPowerMember		 23,947,000us-gaap_DeferredIncomeTaxLiabilities
/ so_DeferredTaxAssetsLiabilitiesAxis
= so_OtherDeferredTaxLiabilitiesMember
/ dei_LegalEntityAxis
= so_GulfPowerMember
Gulf Power [Member] | Other Postretirement Benefits [Member]    
Deferred tax assets -    
Total - deferred tax assets 18,033,000us-gaap_DeferredTaxAssetsGross
/ so_DeferredTaxAssetsLiabilitiesAxis
= us-gaap_OtherPostretirementBenefitPlansDefinedBenefitMember
/ dei_LegalEntityAxis
= so_GulfPowerMember		 17,816,000us-gaap_DeferredTaxAssetsGross
/ so_DeferredTaxAssetsLiabilitiesAxis
= us-gaap_OtherPostretirementBenefitPlansDefinedBenefitMember
/ dei_LegalEntityAxis
= so_GulfPowerMember
Gulf Power [Member] | Tax credit carryforward [Member]    
Deferred tax assets -    
Total - deferred tax assets 18,200,000us-gaap_DeferredTaxAssetsGross
/ so_DeferredTaxAssetsLiabilitiesAxis
= so_TaxCreditCarryforwardMember
/ dei_LegalEntityAxis
= so_GulfPowerMember		 18,420,000us-gaap_DeferredTaxAssetsGross
/ so_DeferredTaxAssetsLiabilitiesAxis
= so_TaxCreditCarryforwardMember
/ dei_LegalEntityAxis
= so_GulfPowerMember
Gulf Power [Member] | Property reserve [Member]    
Deferred tax assets -    
Total - deferred tax assets 13,440,000us-gaap_DeferredTaxAssetsGross
/ so_DeferredTaxAssetsLiabilitiesAxis
= so_PropertyDamageReservesLiabilityMember
/ dei_LegalEntityAxis
= so_GulfPowerMember		 15,144,000us-gaap_DeferredTaxAssetsGross
/ so_DeferredTaxAssetsLiabilitiesAxis
= so_PropertyDamageReservesLiabilityMember
/ dei_LegalEntityAxis
= so_GulfPowerMember
Gulf Power [Member] | Other deferred tax assets [Member]    
Deferred tax assets -    
Total - deferred tax assets 18,893,000us-gaap_DeferredTaxAssetsGross
/ so_DeferredTaxAssetsLiabilitiesAxis
= so_OtherDeferredTaxAssetsMember
/ dei_LegalEntityAxis
= so_GulfPowerMember		 17,780,000us-gaap_DeferredTaxAssetsGross
/ so_DeferredTaxAssetsLiabilitiesAxis
= so_OtherDeferredTaxAssetsMember
/ dei_LegalEntityAxis
= so_GulfPowerMember
Mississippi Power [Member]    
Deferred tax liabilities -    
Total - deferred tax liabilities 146,412,000us-gaap_DeferredTaxLiabilities
/ dei_LegalEntityAxis
= so_MississippiPowerMember		 57,182,000us-gaap_DeferredTaxLiabilities
/ dei_LegalEntityAxis
= so_MississippiPowerMember
Deferred Tax Liabilities, Gross 1,397,851,000us-gaap_DeferredIncomeTaxLiabilities
/ dei_LegalEntityAxis
= so_MississippiPowerMember		 730,649,000us-gaap_DeferredIncomeTaxLiabilities
/ dei_LegalEntityAxis
= so_MississippiPowerMember
Deferred tax assets -    
Total - deferred tax assets 1,251,439,000us-gaap_DeferredTaxAssetsGross
/ dei_LegalEntityAxis
= so_MississippiPowerMember		 673,467,000us-gaap_DeferredTaxAssetsGross
/ dei_LegalEntityAxis
= so_MississippiPowerMember
Portion included in current assets/(liabilities), net 121,049,000so_PortionIncludedInCurrentTaxLiabilitiesCurrentTaxAssetsNet
/ dei_LegalEntityAxis
= so_MississippiPowerMember		 15,626,000so_PortionIncludedInCurrentTaxLiabilitiesCurrentTaxAssetsNet
/ dei_LegalEntityAxis
= so_MississippiPowerMember
Deferred Tax Assets, State Taxes 17,388,000us-gaap_DeferredTaxAssetsStateTaxes
/ dei_LegalEntityAxis
= so_MississippiPowerMember		 0us-gaap_DeferredTaxAssetsStateTaxes
/ dei_LegalEntityAxis
= so_MississippiPowerMember
Accumulated deferred income taxes 284,849,000us-gaap_DeferredTaxLiabilitiesNoncurrent
/ dei_LegalEntityAxis
= so_MississippiPowerMember		 72,808,000us-gaap_DeferredTaxLiabilitiesNoncurrent
/ dei_LegalEntityAxis
= so_MississippiPowerMember
Mississippi Power [Member] | Accelerated depreciation [Member]    
Deferred tax liabilities -    
Deferred Tax Liabilities, Gross 1,068,242,000us-gaap_DeferredIncomeTaxLiabilities
/ so_DeferredTaxAssetsLiabilitiesAxis
= so_AcceleratedDepreciationMember
/ dei_LegalEntityAxis
= so_MississippiPowerMember		 371,553,000us-gaap_DeferredIncomeTaxLiabilities
/ so_DeferredTaxAssetsLiabilitiesAxis
= so_AcceleratedDepreciationMember
/ dei_LegalEntityAxis
= so_MississippiPowerMember
Mississippi Power [Member] | Property basis differences [Member]    
Deferred tax liabilities -    
Deferred Tax Liabilities, Gross 0us-gaap_DeferredIncomeTaxLiabilities
/ so_DeferredTaxAssetsLiabilitiesAxis
= so_PropertyBasisDifferencesMember
/ dei_LegalEntityAxis
= so_MississippiPowerMember		 130,679,000us-gaap_DeferredIncomeTaxLiabilities
/ so_DeferredTaxAssetsLiabilitiesAxis
= so_PropertyBasisDifferencesMember
/ dei_LegalEntityAxis
= so_MississippiPowerMember
Deferred tax assets -    
Total - deferred tax assets 263,430,000us-gaap_DeferredTaxAssetsGross
/ so_DeferredTaxAssetsLiabilitiesAxis
= so_PropertyBasisDifferencesMember
/ dei_LegalEntityAxis
= so_MississippiPowerMember		 0us-gaap_DeferredTaxAssetsGross
/ so_DeferredTaxAssetsLiabilitiesAxis
= so_PropertyBasisDifferencesMember
/ dei_LegalEntityAxis
= so_MississippiPowerMember
Mississippi Power [Member] | Energy Cost Management Clause Over Recovered [Member]    
Deferred tax assets -    
Total - deferred tax assets 905,000us-gaap_DeferredTaxAssetsGross
/ so_DeferredTaxAssetsLiabilitiesAxis
= so_EnergyCostManagementClauseOverRecoveredMember
/ dei_LegalEntityAxis
= so_MississippiPowerMember		 0us-gaap_DeferredTaxAssetsGross
/ so_DeferredTaxAssetsLiabilitiesAxis
= so_EnergyCostManagementClauseOverRecoveredMember
/ dei_LegalEntityAxis
= so_MississippiPowerMember
Mississippi Power [Member] | NOL State Carryforward [Member]    
Deferred tax assets -    
Total - deferred tax assets 56,736,000us-gaap_DeferredTaxAssetsGross
/ so_DeferredTaxAssetsLiabilitiesAxis
= so_NOLStateCarryforwardMember
/ dei_LegalEntityAxis
= so_MississippiPowerMember		 0us-gaap_DeferredTaxAssetsGross
/ so_DeferredTaxAssetsLiabilitiesAxis
= so_NOLStateCarryforwardMember
/ dei_LegalEntityAxis
= so_MississippiPowerMember
Mississippi Power [Member] | Energy Cost Management Clause Under Recovered [Member]    
Deferred tax liabilities -    
Deferred Tax Liabilities, Gross 0us-gaap_DeferredIncomeTaxLiabilities
/ so_DeferredTaxAssetsLiabilitiesAxis
= so_EnergyCostManagementClauseUnderRecoveredMember
/ dei_LegalEntityAxis
= so_MississippiPowerMember		 1,777,000us-gaap_DeferredIncomeTaxLiabilities
/ so_DeferredTaxAssetsLiabilitiesAxis
= so_EnergyCostManagementClauseUnderRecoveredMember
/ dei_LegalEntityAxis
= so_MississippiPowerMember
Mississippi Power [Member] | Pension and other employee benefits [Member]    
Deferred tax liabilities -    
Deferred Tax Liabilities, Gross 35,200,000us-gaap_DeferredIncomeTaxLiabilities
/ so_DeferredTaxAssetsLiabilitiesAxis
= so_PensionAndOtherEmployeeBenefitsMember
/ dei_LegalEntityAxis
= so_MississippiPowerMember		 23,769,000us-gaap_DeferredIncomeTaxLiabilities
/ so_DeferredTaxAssetsLiabilitiesAxis
= so_PensionAndOtherEmployeeBenefitsMember
/ dei_LegalEntityAxis
= so_MississippiPowerMember
Deferred tax assets -    
Total - deferred tax assets 92,232,000us-gaap_DeferredTaxAssetsGross
/ so_DeferredTaxAssetsLiabilitiesAxis
= so_PensionAndOtherEmployeeBenefitsMember
/ dei_LegalEntityAxis
= so_MississippiPowerMember		 57,999,000us-gaap_DeferredTaxAssetsGross
/ so_DeferredTaxAssetsLiabilitiesAxis
= so_PensionAndOtherEmployeeBenefitsMember
/ dei_LegalEntityAxis
= so_MississippiPowerMember
Mississippi Power [Member] | Regulatory assets associated with employee benefit obligations [Member]    
Deferred tax liabilities -    
Deferred Tax Liabilities, Gross 67,727,000us-gaap_DeferredIncomeTaxLiabilities
/ so_DeferredTaxAssetsLiabilitiesAxis
= so_RegulatoryAssetsAssociatedWithEmployeeBenefitObligationsMember
/ dei_LegalEntityAxis
= so_MississippiPowerMember		 33,127,000us-gaap_DeferredIncomeTaxLiabilities
/ so_DeferredTaxAssetsLiabilitiesAxis
= so_RegulatoryAssetsAssociatedWithEmployeeBenefitObligationsMember
/ dei_LegalEntityAxis
= so_MississippiPowerMember
Mississippi Power [Member] | Regulatory assets associated with Kemper IGCC [Member]    
Deferred tax liabilities -    
Deferred Tax Liabilities, Gross 61,561,000us-gaap_DeferredIncomeTaxLiabilities
/ so_DeferredTaxAssetsLiabilitiesAxis
= so_RegulatoryAssetsAssociatedWithKemperIgccMember
/ dei_LegalEntityAxis
= so_MississippiPowerMember		 30,708,000us-gaap_DeferredIncomeTaxLiabilities
/ so_DeferredTaxAssetsLiabilitiesAxis
= so_RegulatoryAssetsAssociatedWithKemperIgccMember
/ dei_LegalEntityAxis
= so_MississippiPowerMember
Mississippi Power [Member] | Under recovered fuel clause [Member]    
Deferred tax liabilities -    
Deferred Tax Liabilities, Gross 3,288,000us-gaap_DeferredIncomeTaxLiabilities
/ so_DeferredTaxAssetsLiabilitiesAxis
= so_UnderRecoveredFuelClauseMember
/ dei_LegalEntityAxis
= so_MississippiPowerMember		 0us-gaap_DeferredIncomeTaxLiabilities
/ so_DeferredTaxAssetsLiabilitiesAxis
= so_UnderRecoveredFuelClauseMember
/ dei_LegalEntityAxis
= so_MississippiPowerMember
Mississippi Power [Member] | Asset retirement obligation [Member]    
Deferred tax assets -    
Total - deferred tax assets 19,299,000us-gaap_DeferredTaxAssetsGross
/ so_DeferredTaxAssetsLiabilitiesAxis
= so_AssetRetirementObligationLiabilityMember
/ dei_LegalEntityAxis
= so_MississippiPowerMember		 16,764,000us-gaap_DeferredTaxAssetsGross
/ so_DeferredTaxAssetsLiabilitiesAxis
= so_AssetRetirementObligationLiabilityMember
/ dei_LegalEntityAxis
= so_MississippiPowerMember
Mississippi Power [Member] | Regulatory assets associated with asset retirement obligations [Member]    
Deferred tax liabilities -    
Deferred Tax Liabilities, Gross 19,299,000us-gaap_DeferredIncomeTaxLiabilities
/ so_DeferredTaxAssetsLiabilitiesAxis
= so_RegulatoryAssetsAssociatedWithAssetRetirementObligationsMember
/ dei_LegalEntityAxis
= so_MississippiPowerMember		 16,764,000us-gaap_DeferredIncomeTaxLiabilities
/ so_DeferredTaxAssetsLiabilitiesAxis
= so_RegulatoryAssetsAssociatedWithAssetRetirementObligationsMember
/ dei_LegalEntityAxis
= so_MississippiPowerMember
Mississippi Power [Member] | Rate Differential [Member]    
Deferred tax liabilities -    
Deferred Tax Liabilities, Gross 89,040,000us-gaap_DeferredIncomeTaxLiabilities
/ so_DeferredTaxAssetsLiabilitiesAxis
= so_RateDifferentialMember
/ dei_LegalEntityAxis
= so_MississippiPowerMember		 56,074,000us-gaap_DeferredIncomeTaxLiabilities
/ so_DeferredTaxAssetsLiabilitiesAxis
= so_RateDifferentialMember
/ dei_LegalEntityAxis
= so_MississippiPowerMember
Mississippi Power [Member] | Federal effect of state deferred taxes [Member]    
Deferred tax liabilities -    
Deferred Tax Liabilities, Gross 1,279,000us-gaap_DeferredIncomeTaxLiabilities
/ so_DeferredTaxAssetsLiabilitiesAxis
= so_FederalEffectOfStateDeferredTaxesMember
/ dei_LegalEntityAxis
= so_MississippiPowerMember		 30,615,000us-gaap_DeferredIncomeTaxLiabilities
/ so_DeferredTaxAssetsLiabilitiesAxis
= so_FederalEffectOfStateDeferredTaxesMember
/ dei_LegalEntityAxis
= so_MississippiPowerMember
Mississippi Power [Member] | Other deferred tax liabilities [Member]    
Deferred tax liabilities -    
Deferred Tax Liabilities, Gross 52,215,000us-gaap_DeferredIncomeTaxLiabilities
/ so_DeferredTaxAssetsLiabilitiesAxis
= so_OtherDeferredTaxLiabilitiesMember
/ dei_LegalEntityAxis
= so_MississippiPowerMember		 35,583,000us-gaap_DeferredIncomeTaxLiabilities
/ so_DeferredTaxAssetsLiabilitiesAxis
= so_OtherDeferredTaxLiabilitiesMember
/ dei_LegalEntityAxis
= so_MississippiPowerMember
Mississippi Power [Member] | Property insurance [Member]    
Deferred tax assets -    
Total - deferred tax assets 24,315,000us-gaap_DeferredTaxAssetsGross
/ so_DeferredTaxAssetsLiabilitiesAxis
= so_PropertyInsuranceMember
/ dei_LegalEntityAxis
= so_MississippiPowerMember		 23,693,000us-gaap_DeferredTaxAssetsGross
/ so_DeferredTaxAssetsLiabilitiesAxis
= so_PropertyInsuranceMember
/ dei_LegalEntityAxis
= so_MississippiPowerMember
Mississippi Power [Member] | Premium on long-term debt [Member]    
Deferred tax assets -    
Total - deferred tax assets 20,694,000us-gaap_DeferredTaxAssetsGross
/ so_DeferredTaxAssetsLiabilitiesAxis
= so_PremiumOnLongTermDebtMember
/ dei_LegalEntityAxis
= so_MississippiPowerMember		 23,736,000us-gaap_DeferredTaxAssetsGross
/ so_DeferredTaxAssetsLiabilitiesAxis
= so_PremiumOnLongTermDebtMember
/ dei_LegalEntityAxis
= so_MississippiPowerMember
Mississippi Power [Member] | Unbilled revenues [Member]    
Deferred tax assets -    
Total - deferred tax assets 14,535,000us-gaap_DeferredTaxAssetsGross
/ so_DeferredTaxAssetsLiabilitiesAxis
= us-gaap_UnbilledRevenuesMember
/ dei_LegalEntityAxis
= so_MississippiPowerMember		 12,136,000us-gaap_DeferredTaxAssetsGross
/ so_DeferredTaxAssetsLiabilitiesAxis
= us-gaap_UnbilledRevenuesMember
/ dei_LegalEntityAxis
= so_MississippiPowerMember
Mississippi Power [Member] | Over recovered fuel clause [Member]    
Deferred tax assets -    
Total - deferred tax assets 0us-gaap_DeferredTaxAssetsGross
/ so_DeferredTaxAssetsLiabilitiesAxis
= so_OverRecoveredFuelClauseMember
/ dei_LegalEntityAxis
= so_MississippiPowerMember		 7,741,000us-gaap_DeferredTaxAssetsGross
/ so_DeferredTaxAssetsLiabilitiesAxis
= so_OverRecoveredFuelClauseMember
/ dei_LegalEntityAxis
= so_MississippiPowerMember
Mississippi Power [Member] | Kemper IGCC Loss [Member]    
Deferred tax assets -    
Total - deferred tax assets 631,326,000us-gaap_DeferredTaxAssetsGross
/ so_DeferredTaxAssetsLiabilitiesAxis
= so_KemperIGCCLossMember
/ dei_LegalEntityAxis
= so_MississippiPowerMember		 472,000,000us-gaap_DeferredTaxAssetsGross
/ so_DeferredTaxAssetsLiabilitiesAxis
= so_KemperIGCCLossMember
/ dei_LegalEntityAxis
= so_MississippiPowerMember
Mississippi Power [Member] | Interest rate hedges [Member]    
Deferred tax assets -    
Total - deferred tax assets 4,544,000us-gaap_DeferredTaxAssetsGross
/ so_DeferredTaxAssetsLiabilitiesAxis
= us-gaap_InterestRateSwapMember
/ dei_LegalEntityAxis
= so_MississippiPowerMember		 5,094,000us-gaap_DeferredTaxAssetsGross
/ so_DeferredTaxAssetsLiabilitiesAxis
= us-gaap_InterestRateSwapMember
/ dei_LegalEntityAxis
= so_MississippiPowerMember
Mississippi Power [Member] | Kemper Rate Factor - Regulatory Liability Retail [Member]    
Deferred tax assets -    
Total - deferred tax assets 108,312,000us-gaap_DeferredTaxAssetsGross
/ so_DeferredTaxAssetsLiabilitiesAxis
= so_KemperRateFactorRegulatoryLiabilityRetailMember
/ dei_LegalEntityAxis
= so_MississippiPowerMember		 36,210,000us-gaap_DeferredTaxAssetsGross
/ so_DeferredTaxAssetsLiabilitiesAxis
= so_KemperRateFactorRegulatoryLiabilityRetailMember
/ dei_LegalEntityAxis
= so_MississippiPowerMember
Mississippi Power [Member] | Other deferred tax assets [Member]    
Deferred tax assets -    
Total - deferred tax assets 15,111,000us-gaap_DeferredTaxAssetsGross
/ so_DeferredTaxAssetsLiabilitiesAxis
= so_OtherDeferredTaxAssetsMember
/ dei_LegalEntityAxis
= so_MississippiPowerMember		 18,094,000us-gaap_DeferredTaxAssetsGross
/ so_DeferredTaxAssetsLiabilitiesAxis
= so_OtherDeferredTaxAssetsMember
/ dei_LegalEntityAxis
= so_MississippiPowerMember
Southern Power [Member]    
Deferred tax liabilities -    
Total - deferred tax liabilities 559,200,000us-gaap_DeferredTaxLiabilities
/ dei_LegalEntityAxis
= so_SouthernPowerMember		 724,200,000us-gaap_DeferredTaxLiabilities
/ dei_LegalEntityAxis
= so_SouthernPowerMember
Deferred Tax Liabilities, Gross 1,031,900,000us-gaap_DeferredIncomeTaxLiabilities
/ dei_LegalEntityAxis
= so_SouthernPowerMember		 844,400,000us-gaap_DeferredIncomeTaxLiabilities
/ dei_LegalEntityAxis
= so_SouthernPowerMember
Deferred tax assets -    
Total - deferred tax assets 480,200,000us-gaap_DeferredTaxAssetsGross
/ dei_LegalEntityAxis
= so_SouthernPowerMember		 127,700,000us-gaap_DeferredTaxAssetsGross
/ dei_LegalEntityAxis
= so_SouthernPowerMember
Total deferred tax liabilities, net 472,700,000us-gaap_DeferredTaxAssetsLiabilitiesNet
/ dei_LegalEntityAxis
= so_SouthernPowerMember		 120,200,000us-gaap_DeferredTaxAssetsLiabilitiesNet
/ dei_LegalEntityAxis
= so_SouthernPowerMember
Portion included in current assets/(liabilities), net 303,600,000so_PortionIncludedInCurrentTaxLiabilitiesCurrentTaxAssetsNet
/ dei_LegalEntityAxis
= so_SouthernPowerMember		 200,000so_PortionIncludedInCurrentTaxLiabilitiesCurrentTaxAssetsNet
/ dei_LegalEntityAxis
= so_SouthernPowerMember
Valuation allowance (7,500,000)us-gaap_DeferredTaxAssetsValuationAllowance
/ dei_LegalEntityAxis
= so_SouthernPowerMember		 (7,500,000)us-gaap_DeferredTaxAssetsValuationAllowance
/ dei_LegalEntityAxis
= so_SouthernPowerMember
Accumulated deferred income taxes 862,795,000us-gaap_DeferredTaxLiabilitiesNoncurrent
/ dei_LegalEntityAxis
= so_SouthernPowerMember		 724,390,000us-gaap_DeferredTaxLiabilitiesNoncurrent
/ dei_LegalEntityAxis
= so_SouthernPowerMember
Southern Power [Member] | Accelerated depreciation and other property basis differences [Member]    
Deferred tax liabilities -    
Deferred Tax Liabilities, Gross 1,006,500,000us-gaap_DeferredIncomeTaxLiabilities
/ so_DeferredTaxAssetsLiabilitiesAxis
= so_AcceleratedDepreciationAndOtherPropertyBasisDifferencesMember
/ dei_LegalEntityAxis
= so_SouthernPowerMember		 829,500,000us-gaap_DeferredIncomeTaxLiabilities
/ so_DeferredTaxAssetsLiabilitiesAxis
= so_AcceleratedDepreciationAndOtherPropertyBasisDifferencesMember
/ dei_LegalEntityAxis
= so_SouthernPowerMember
Southern Power [Member] | Federal effect of state deferred taxes [Member]    
Deferred tax assets -    
Total - deferred tax assets 28,900,000us-gaap_DeferredTaxAssetsGross
/ so_DeferredTaxAssetsLiabilitiesAxis
= so_FederalEffectOfStateDeferredTaxesMember
/ dei_LegalEntityAxis
= so_SouthernPowerMember		 29,700,000us-gaap_DeferredTaxAssetsGross
/ so_DeferredTaxAssetsLiabilitiesAxis
= so_FederalEffectOfStateDeferredTaxesMember
/ dei_LegalEntityAxis
= so_SouthernPowerMember
Southern Power [Member] | Levelized capacity revenues [Member]    
Deferred tax liabilities -    
Deferred Tax Liabilities, Gross 17,100,000us-gaap_DeferredIncomeTaxLiabilities
/ so_DeferredTaxAssetsLiabilitiesAxis
= so_LevelizedRevenuesMember
/ dei_LegalEntityAxis
= so_SouthernPowerMember		 11,200,000us-gaap_DeferredIncomeTaxLiabilities
/ so_DeferredTaxAssetsLiabilitiesAxis
= so_LevelizedRevenuesMember
/ dei_LegalEntityAxis
= so_SouthernPowerMember
Deferred tax assets -    
Total - deferred tax assets 4,900,000us-gaap_DeferredTaxAssetsGross
/ so_DeferredTaxAssetsLiabilitiesAxis
= so_LevelizedRevenuesMember
/ dei_LegalEntityAxis
= so_SouthernPowerMember		 6,000,000us-gaap_DeferredTaxAssetsGross
/ so_DeferredTaxAssetsLiabilitiesAxis
= so_LevelizedRevenuesMember
/ dei_LegalEntityAxis
= so_SouthernPowerMember
Southern Power [Member] | State Net Operating Loss [Member]    
Deferred tax assets -    
Total - deferred tax assets 14,500,000us-gaap_DeferredTaxAssetsGross
/ so_DeferredTaxAssetsLiabilitiesAxis
= so_StateNetOperatingLossMember
/ dei_LegalEntityAxis
= so_SouthernPowerMember		 17,000,000us-gaap_DeferredTaxAssetsGross
/ so_DeferredTaxAssetsLiabilitiesAxis
= so_StateNetOperatingLossMember
/ dei_LegalEntityAxis
= so_SouthernPowerMember
Southern Power [Member] | Other deferred tax liabilities [Member]    
Deferred tax liabilities -    
Deferred Tax Liabilities, Gross 5,700,000us-gaap_DeferredIncomeTaxLiabilities
/ so_DeferredTaxAssetsLiabilitiesAxis
= so_OtherDeferredTaxLiabilitiesMember
/ dei_LegalEntityAxis
= so_SouthernPowerMember		 900,000us-gaap_DeferredIncomeTaxLiabilities
/ so_DeferredTaxAssetsLiabilitiesAxis
= so_OtherDeferredTaxLiabilitiesMember
/ dei_LegalEntityAxis
= so_SouthernPowerMember
Southern Power [Member] | Other property basis differences [Member]    
Deferred tax liabilities -    
Deferred Tax Liabilities, Gross 2,600,000us-gaap_DeferredIncomeTaxLiabilities
/ so_DeferredTaxAssetsLiabilitiesAxis
= so_OtherPropertyBasisDifferencesMember
/ dei_LegalEntityAxis
= so_SouthernPowerMember		 2,800,000us-gaap_DeferredIncomeTaxLiabilities
/ so_DeferredTaxAssetsLiabilitiesAxis
= so_OtherPropertyBasisDifferencesMember
/ dei_LegalEntityAxis
= so_SouthernPowerMember
Southern Power [Member] | Tax credit carryforward [Member]    
Deferred tax assets -    
Total - deferred tax assets 15,000,000us-gaap_DeferredTaxAssetsGross
/ so_DeferredTaxAssetsLiabilitiesAxis
= so_TaxCreditCarryforwardMember
/ dei_LegalEntityAxis
= so_SouthernPowerMember		 1,100,000us-gaap_DeferredTaxAssetsGross
/ so_DeferredTaxAssetsLiabilitiesAxis
= so_TaxCreditCarryforwardMember
/ dei_LegalEntityAxis
= so_SouthernPowerMember
Southern Power [Member] | Unrealized Tax Credits [Member]    
Deferred tax assets -    
Total - deferred tax assets 305,200,000us-gaap_DeferredTaxAssetsGross
/ so_DeferredTaxAssetsLiabilitiesAxis
= so_UnrealizedTaxCreditsMember
/ dei_LegalEntityAxis
= so_SouthernPowerMember		 0us-gaap_DeferredTaxAssetsGross
/ so_DeferredTaxAssetsLiabilitiesAxis
= so_UnrealizedTaxCreditsMember
/ dei_LegalEntityAxis
= so_SouthernPowerMember
Southern Power [Member] | Investment tax credit carryforward [Member]    
Deferred tax assets -    
Total - deferred tax assets 101,500,000us-gaap_DeferredTaxAssetsGross
/ so_DeferredTaxAssetsLiabilitiesAxis
= us-gaap_InvestmentCreditMember
/ dei_LegalEntityAxis
= so_SouthernPowerMember		 58,000,000us-gaap_DeferredTaxAssetsGross
/ so_DeferredTaxAssetsLiabilitiesAxis
= us-gaap_InvestmentCreditMember
/ dei_LegalEntityAxis
= so_SouthernPowerMember
Southern Power [Member] | Unrealized Loss [Member]    
Deferred tax assets -    
Total - deferred tax assets 6,100,000us-gaap_DeferredTaxAssetsGross
/ so_DeferredTaxAssetsLiabilitiesAxis
= so_UnrealizedLossMember
/ dei_LegalEntityAxis
= so_SouthernPowerMember		 11,200,000us-gaap_DeferredTaxAssetsGross
/ so_DeferredTaxAssetsLiabilitiesAxis
= so_UnrealizedLossMember
/ dei_LegalEntityAxis
= so_SouthernPowerMember
Southern Power [Member] | Other deferred tax assets [Member]    
Deferred tax assets -    
Total - deferred tax assets $ 4,100,000us-gaap_DeferredTaxAssetsGross
/ so_DeferredTaxAssetsLiabilitiesAxis
= so_OtherDeferredTaxAssetsMember
/ dei_LegalEntityAxis
= so_SouthernPowerMember		 $ 4,700,000us-gaap_DeferredTaxAssetsGross
/ so_DeferredTaxAssetsLiabilitiesAxis
= so_OtherDeferredTaxAssetsMember
/ dei_LegalEntityAxis
= so_SouthernPowerMember