XML 1101 R94.htm IDEA: XBRL DOCUMENT v2.4.1.9
Derivatives - Balance Sheet Offsetting (Details) (USD $)
Dec. 31, 2014
Dec. 31, 2013
Derivative [Line Items]    
Derivative Asset, Fair Value, Gross Asset $ 21,000,000us-gaap_DerivativeFairValueOfDerivativeAsset $ 27,000,000us-gaap_DerivativeFairValueOfDerivativeAsset
Derivative Liability, Fair Value, Gross Liability 225,000,000us-gaap_DerivativeFairValueOfDerivativeLiability 56,000,000us-gaap_DerivativeFairValueOfDerivativeLiability
Alabama Power [Member]    
Derivative [Line Items]    
Derivative Asset, Fair Value, Gross Asset 1,000,000us-gaap_DerivativeFairValueOfDerivativeAsset
/ dei_LegalEntityAxis
= so_AlabamaPowerMember		 7,000,000us-gaap_DerivativeFairValueOfDerivativeAsset
/ dei_LegalEntityAxis
= so_AlabamaPowerMember
Derivative Liability, Fair Value, Gross Liability 61,000,000us-gaap_DerivativeFairValueOfDerivativeLiability
/ dei_LegalEntityAxis
= so_AlabamaPowerMember		 8,000,000us-gaap_DerivativeFairValueOfDerivativeLiability
/ dei_LegalEntityAxis
= so_AlabamaPowerMember
Mississippi Power [Member]    
Derivative [Line Items]    
Derivative Asset, Fair Value, Gross Asset 52,000us-gaap_DerivativeFairValueOfDerivativeAsset
/ dei_LegalEntityAxis
= so_MississippiPowerMember		 4,803,000us-gaap_DerivativeFairValueOfDerivativeAsset
/ dei_LegalEntityAxis
= so_MississippiPowerMember
Derivative Liability, Fair Value, Gross Liability 45,418,000us-gaap_DerivativeFairValueOfDerivativeLiability
/ dei_LegalEntityAxis
= so_MississippiPowerMember		 10,282,000us-gaap_DerivativeFairValueOfDerivativeLiability
/ dei_LegalEntityAxis
= so_MississippiPowerMember
Energy Related Derivative [Member]    
Derivative [Line Items]    
Derivative Asset, Fair Value, Amount Offset Against Collateral 4,000,000us-gaap_DerivativeFairValueOfDerivativeAssetAmountOffsetAgainstCollateral
/ us-gaap_DerivativeInstrumentRiskAxis
= us-gaap_EnergyRelatedDerivativeMember		 2,000,000us-gaap_DerivativeFairValueOfDerivativeAssetAmountOffsetAgainstCollateral
/ us-gaap_DerivativeInstrumentRiskAxis
= us-gaap_EnergyRelatedDerivativeMember
Derivative Liability, Fair Value, Amount Offset Against Collateral 192,000,000us-gaap_DerivativeFairValueOfDerivativeLiabilityAmountOffsetAgainstCollateral
/ us-gaap_DerivativeInstrumentRiskAxis
= us-gaap_EnergyRelatedDerivativeMember		 34,000,000us-gaap_DerivativeFairValueOfDerivativeLiabilityAmountOffsetAgainstCollateral
/ us-gaap_DerivativeInstrumentRiskAxis
= us-gaap_EnergyRelatedDerivativeMember
Energy Related Derivative [Member] | Alabama Power [Member]    
Derivative [Line Items]    
Derivative Asset, Fair Value, Amount Offset Against Collateral 1,000,000us-gaap_DerivativeFairValueOfDerivativeAssetAmountOffsetAgainstCollateral
/ us-gaap_DerivativeInstrumentRiskAxis
= us-gaap_EnergyRelatedDerivativeMember
/ dei_LegalEntityAxis
= so_AlabamaPowerMember		 2,000,000us-gaap_DerivativeFairValueOfDerivativeAssetAmountOffsetAgainstCollateral
/ us-gaap_DerivativeInstrumentRiskAxis
= us-gaap_EnergyRelatedDerivativeMember
/ dei_LegalEntityAxis
= so_AlabamaPowerMember
Derivative Liability, Fair Value, Amount Offset Against Collateral 53,000,000us-gaap_DerivativeFairValueOfDerivativeLiabilityAmountOffsetAgainstCollateral
/ us-gaap_DerivativeInstrumentRiskAxis
= us-gaap_EnergyRelatedDerivativeMember
/ dei_LegalEntityAxis
= so_AlabamaPowerMember		 3,000,000us-gaap_DerivativeFairValueOfDerivativeLiabilityAmountOffsetAgainstCollateral
/ us-gaap_DerivativeInstrumentRiskAxis
= us-gaap_EnergyRelatedDerivativeMember
/ dei_LegalEntityAxis
= so_AlabamaPowerMember
Energy Related Derivative [Member] | Georgia Power [Member]    
Derivative [Line Items]    
Derivative Asset, Fair Value, Amount Offset Against Collateral 0us-gaap_DerivativeFairValueOfDerivativeAssetAmountOffsetAgainstCollateral
/ us-gaap_DerivativeInstrumentRiskAxis
= us-gaap_EnergyRelatedDerivativeMember
/ dei_LegalEntityAxis
= so_GeorgiaPowerMember		 0us-gaap_DerivativeFairValueOfDerivativeAssetAmountOffsetAgainstCollateral
/ us-gaap_DerivativeInstrumentRiskAxis
= us-gaap_EnergyRelatedDerivativeMember
/ dei_LegalEntityAxis
= so_GeorgiaPowerMember
Derivative Liability, Fair Value, Amount Offset Against Collateral 20,000,000us-gaap_DerivativeFairValueOfDerivativeLiabilityAmountOffsetAgainstCollateral
/ us-gaap_DerivativeInstrumentRiskAxis
= us-gaap_EnergyRelatedDerivativeMember
/ dei_LegalEntityAxis
= so_GeorgiaPowerMember		 16,000,000us-gaap_DerivativeFairValueOfDerivativeLiabilityAmountOffsetAgainstCollateral
/ us-gaap_DerivativeInstrumentRiskAxis
= us-gaap_EnergyRelatedDerivativeMember
/ dei_LegalEntityAxis
= so_GeorgiaPowerMember
Energy Related Derivative [Member] | Gulf Power [Member]    
Derivative [Line Items]    
Derivative Asset, Fair Value, Amount Offset Against Collateral 2,000us-gaap_DerivativeFairValueOfDerivativeAssetAmountOffsetAgainstCollateral
/ us-gaap_DerivativeInstrumentRiskAxis
= us-gaap_EnergyRelatedDerivativeMember
/ dei_LegalEntityAxis
= so_GulfPowerMember		 1,187,000us-gaap_DerivativeFairValueOfDerivativeAssetAmountOffsetAgainstCollateral
/ us-gaap_DerivativeInstrumentRiskAxis
= us-gaap_EnergyRelatedDerivativeMember
/ dei_LegalEntityAxis
= so_GulfPowerMember
Derivative Liability, Fair Value, Amount Offset Against Collateral 72,312,000us-gaap_DerivativeFairValueOfDerivativeLiabilityAmountOffsetAgainstCollateral
/ us-gaap_DerivativeInstrumentRiskAxis
= us-gaap_EnergyRelatedDerivativeMember
/ dei_LegalEntityAxis
= so_GulfPowerMember		 11,268,000us-gaap_DerivativeFairValueOfDerivativeLiabilityAmountOffsetAgainstCollateral
/ us-gaap_DerivativeInstrumentRiskAxis
= us-gaap_EnergyRelatedDerivativeMember
/ dei_LegalEntityAxis
= so_GulfPowerMember
Energy Related Derivative [Member] | Mississippi Power [Member]    
Derivative [Line Items]    
Derivative Asset, Fair Value, Amount Offset Against Collateral 1,000us-gaap_DerivativeFairValueOfDerivativeAssetAmountOffsetAgainstCollateral
/ us-gaap_DerivativeInstrumentRiskAxis
= us-gaap_EnergyRelatedDerivativeMember
/ dei_LegalEntityAxis
= so_MississippiPowerMember		 947,000us-gaap_DerivativeFairValueOfDerivativeAssetAmountOffsetAgainstCollateral
/ us-gaap_DerivativeInstrumentRiskAxis
= us-gaap_EnergyRelatedDerivativeMember
/ dei_LegalEntityAxis
= so_MississippiPowerMember
Derivative Liability, Fair Value, Amount Offset Against Collateral 45,365,000us-gaap_DerivativeFairValueOfDerivativeLiabilityAmountOffsetAgainstCollateral
/ us-gaap_DerivativeInstrumentRiskAxis
= us-gaap_EnergyRelatedDerivativeMember
/ dei_LegalEntityAxis
= so_MississippiPowerMember		 6,426,000us-gaap_DerivativeFairValueOfDerivativeLiabilityAmountOffsetAgainstCollateral
/ us-gaap_DerivativeInstrumentRiskAxis
= us-gaap_EnergyRelatedDerivativeMember
/ dei_LegalEntityAxis
= so_MississippiPowerMember
Energy Related Derivative [Member] | Southern Power [Member]    
Derivative [Line Items]    
Derivative Asset, Fair Value, Amount Offset Against Collateral 5,400,000us-gaap_DerivativeFairValueOfDerivativeAssetAmountOffsetAgainstCollateral
/ us-gaap_DerivativeInstrumentRiskAxis
= us-gaap_EnergyRelatedDerivativeMember
/ dei_LegalEntityAxis
= so_SouthernPowerMember		 500,000us-gaap_DerivativeFairValueOfDerivativeAssetAmountOffsetAgainstCollateral
/ us-gaap_DerivativeInstrumentRiskAxis
= us-gaap_EnergyRelatedDerivativeMember
/ dei_LegalEntityAxis
= so_SouthernPowerMember
Derivative Liability, Fair Value, Amount Offset Against Collateral 3,500,000us-gaap_DerivativeFairValueOfDerivativeLiabilityAmountOffsetAgainstCollateral
/ us-gaap_DerivativeInstrumentRiskAxis
= us-gaap_EnergyRelatedDerivativeMember
/ dei_LegalEntityAxis
= so_SouthernPowerMember		 500,000us-gaap_DerivativeFairValueOfDerivativeLiabilityAmountOffsetAgainstCollateral
/ us-gaap_DerivativeInstrumentRiskAxis
= us-gaap_EnergyRelatedDerivativeMember
/ dei_LegalEntityAxis
= so_SouthernPowerMember
Interest Rate Contract [Member]    
Derivative [Line Items]    
Derivative Asset, Fair Value, Amount Offset Against Collateral 0us-gaap_DerivativeFairValueOfDerivativeAssetAmountOffsetAgainstCollateral
/ us-gaap_DerivativeInstrumentRiskAxis
= us-gaap_InterestRateContractMember		 3,000,000us-gaap_DerivativeFairValueOfDerivativeAssetAmountOffsetAgainstCollateral
/ us-gaap_DerivativeInstrumentRiskAxis
= us-gaap_InterestRateContractMember
Derivative Liability, Fair Value, Amount Offset Against Collateral 16,000,000us-gaap_DerivativeFairValueOfDerivativeLiabilityAmountOffsetAgainstCollateral
/ us-gaap_DerivativeInstrumentRiskAxis
= us-gaap_InterestRateContractMember		 0us-gaap_DerivativeFairValueOfDerivativeLiabilityAmountOffsetAgainstCollateral
/ us-gaap_DerivativeInstrumentRiskAxis
= us-gaap_InterestRateContractMember
Interest Rate Contract [Member] | Georgia Power [Member]    
Derivative [Line Items]    
Derivative Asset, Fair Value, Amount Offset Against Collateral 0us-gaap_DerivativeFairValueOfDerivativeAssetAmountOffsetAgainstCollateral
/ us-gaap_DerivativeInstrumentRiskAxis
= us-gaap_InterestRateContractMember
/ dei_LegalEntityAxis
= so_GeorgiaPowerMember		 0us-gaap_DerivativeFairValueOfDerivativeAssetAmountOffsetAgainstCollateral
/ us-gaap_DerivativeInstrumentRiskAxis
= us-gaap_InterestRateContractMember
/ dei_LegalEntityAxis
= so_GeorgiaPowerMember
Derivative Liability, Fair Value, Amount Offset Against Collateral 8,000,000us-gaap_DerivativeFairValueOfDerivativeLiabilityAmountOffsetAgainstCollateral
/ us-gaap_DerivativeInstrumentRiskAxis
= us-gaap_InterestRateContractMember
/ dei_LegalEntityAxis
= so_GeorgiaPowerMember		 0us-gaap_DerivativeFairValueOfDerivativeLiabilityAmountOffsetAgainstCollateral
/ us-gaap_DerivativeInstrumentRiskAxis
= us-gaap_InterestRateContractMember
/ dei_LegalEntityAxis
= so_GeorgiaPowerMember
Net Amount Of Derivatives [Member] | Energy Related Derivative [Member]    
Derivative [Line Items]    
Derivative Asset, Fair Value, Gross Asset 13,000,000us-gaap_DerivativeFairValueOfDerivativeAsset
/ us-gaap_BalanceSheetLocationAxis
= so_NetAmountOfDerivativesMember
/ us-gaap_DerivativeInstrumentRiskAxis
= us-gaap_EnergyRelatedDerivativeMember		 [1] 24,000,000us-gaap_DerivativeFairValueOfDerivativeAsset
/ us-gaap_BalanceSheetLocationAxis
= so_NetAmountOfDerivativesMember
/ us-gaap_DerivativeInstrumentRiskAxis
= us-gaap_EnergyRelatedDerivativeMember		 [1]
Derivative Liability, Fair Value, Gross Liability 201,000,000us-gaap_DerivativeFairValueOfDerivativeLiability
/ us-gaap_BalanceSheetLocationAxis
= so_NetAmountOfDerivativesMember
/ us-gaap_DerivativeInstrumentRiskAxis
= us-gaap_EnergyRelatedDerivativeMember		 [1] 56,000,000us-gaap_DerivativeFairValueOfDerivativeLiability
/ us-gaap_BalanceSheetLocationAxis
= so_NetAmountOfDerivativesMember
/ us-gaap_DerivativeInstrumentRiskAxis
= us-gaap_EnergyRelatedDerivativeMember		 [1]
Net Amount Of Derivatives [Member] | Energy Related Derivative [Member] | Alabama Power [Member]    
Derivative [Line Items]    
Derivative Asset, Fair Value, Gross Asset 1,000,000us-gaap_DerivativeFairValueOfDerivativeAsset
/ us-gaap_BalanceSheetLocationAxis
= so_NetAmountOfDerivativesMember
/ us-gaap_DerivativeInstrumentRiskAxis
= us-gaap_EnergyRelatedDerivativeMember
/ dei_LegalEntityAxis
= so_AlabamaPowerMember		 [1] 7,000,000us-gaap_DerivativeFairValueOfDerivativeAsset
/ us-gaap_BalanceSheetLocationAxis
= so_NetAmountOfDerivativesMember
/ us-gaap_DerivativeInstrumentRiskAxis
= us-gaap_EnergyRelatedDerivativeMember
/ dei_LegalEntityAxis
= so_AlabamaPowerMember		 [1]
Derivative Liability, Fair Value, Gross Liability 53,000,000us-gaap_DerivativeFairValueOfDerivativeLiability
/ us-gaap_BalanceSheetLocationAxis
= so_NetAmountOfDerivativesMember
/ us-gaap_DerivativeInstrumentRiskAxis
= us-gaap_EnergyRelatedDerivativeMember
/ dei_LegalEntityAxis
= so_AlabamaPowerMember		 [1] 8,000,000us-gaap_DerivativeFairValueOfDerivativeLiability
/ us-gaap_BalanceSheetLocationAxis
= so_NetAmountOfDerivativesMember
/ us-gaap_DerivativeInstrumentRiskAxis
= us-gaap_EnergyRelatedDerivativeMember
/ dei_LegalEntityAxis
= so_AlabamaPowerMember		 [1]
Net Amount Of Derivatives [Member] | Energy Related Derivative [Member] | Georgia Power [Member]    
Derivative [Line Items]    
Derivative Asset, Fair Value, Gross Asset 7,000,000us-gaap_DerivativeFairValueOfDerivativeAsset
/ us-gaap_BalanceSheetLocationAxis
= so_NetAmountOfDerivativesMember
/ us-gaap_DerivativeInstrumentRiskAxis
= us-gaap_EnergyRelatedDerivativeMember
/ dei_LegalEntityAxis
= so_GeorgiaPowerMember		 [1] 5,000,000us-gaap_DerivativeFairValueOfDerivativeAsset
/ us-gaap_BalanceSheetLocationAxis
= so_NetAmountOfDerivativesMember
/ us-gaap_DerivativeInstrumentRiskAxis
= us-gaap_EnergyRelatedDerivativeMember
/ dei_LegalEntityAxis
= so_GeorgiaPowerMember		 [1]
Derivative Liability, Fair Value, Gross Liability 27,000,000us-gaap_DerivativeFairValueOfDerivativeLiability
/ us-gaap_BalanceSheetLocationAxis
= so_NetAmountOfDerivativesMember
/ us-gaap_DerivativeInstrumentRiskAxis
= us-gaap_EnergyRelatedDerivativeMember
/ dei_LegalEntityAxis
= so_GeorgiaPowerMember		 [1] 21,000,000us-gaap_DerivativeFairValueOfDerivativeLiability
/ us-gaap_BalanceSheetLocationAxis
= so_NetAmountOfDerivativesMember
/ us-gaap_DerivativeInstrumentRiskAxis
= us-gaap_EnergyRelatedDerivativeMember
/ dei_LegalEntityAxis
= so_GeorgiaPowerMember		 [1]
Net Amount Of Derivatives [Member] | Energy Related Derivative [Member] | Gulf Power [Member]    
Derivative [Line Items]    
Derivative Asset, Fair Value, Gross Asset 125,000us-gaap_DerivativeFairValueOfDerivativeAsset
/ us-gaap_BalanceSheetLocationAxis
= so_NetAmountOfDerivativesMember
/ us-gaap_DerivativeInstrumentRiskAxis
= us-gaap_EnergyRelatedDerivativeMember
/ dei_LegalEntityAxis
= so_GulfPowerMember		 [1] 6,962,000us-gaap_DerivativeFairValueOfDerivativeAsset
/ us-gaap_BalanceSheetLocationAxis
= so_NetAmountOfDerivativesMember
/ us-gaap_DerivativeInstrumentRiskAxis
= us-gaap_EnergyRelatedDerivativeMember
/ dei_LegalEntityAxis
= so_GulfPowerMember		 [1]
Derivative Liability, Fair Value, Gross Liability 72,435,000us-gaap_DerivativeFairValueOfDerivativeLiability
/ us-gaap_BalanceSheetLocationAxis
= so_NetAmountOfDerivativesMember
/ us-gaap_DerivativeInstrumentRiskAxis
= us-gaap_EnergyRelatedDerivativeMember
/ dei_LegalEntityAxis
= so_GulfPowerMember		 [1] 17,043,000us-gaap_DerivativeFairValueOfDerivativeLiability
/ us-gaap_BalanceSheetLocationAxis
= so_NetAmountOfDerivativesMember
/ us-gaap_DerivativeInstrumentRiskAxis
= us-gaap_EnergyRelatedDerivativeMember
/ dei_LegalEntityAxis
= so_GulfPowerMember		 [1]
Net Amount Of Derivatives [Member] | Energy Related Derivative [Member] | Mississippi Power [Member]    
Derivative [Line Items]    
Derivative Asset, Fair Value, Gross Asset 65,000us-gaap_DerivativeFairValueOfDerivativeAsset
/ us-gaap_BalanceSheetLocationAxis
= so_NetAmountOfDerivativesMember
/ us-gaap_DerivativeInstrumentRiskAxis
= us-gaap_EnergyRelatedDerivativeMember
/ dei_LegalEntityAxis
= so_MississippiPowerMember		 [1] 4,803,000us-gaap_DerivativeFairValueOfDerivativeAsset
/ us-gaap_BalanceSheetLocationAxis
= so_NetAmountOfDerivativesMember
/ us-gaap_DerivativeInstrumentRiskAxis
= us-gaap_EnergyRelatedDerivativeMember
/ dei_LegalEntityAxis
= so_MississippiPowerMember		 [1]
Derivative Liability, Fair Value, Gross Liability 45,429,000us-gaap_DerivativeFairValueOfDerivativeLiability
/ us-gaap_BalanceSheetLocationAxis
= so_NetAmountOfDerivativesMember
/ us-gaap_DerivativeInstrumentRiskAxis
= us-gaap_EnergyRelatedDerivativeMember
/ dei_LegalEntityAxis
= so_MississippiPowerMember		 [1] 10,282,000us-gaap_DerivativeFairValueOfDerivativeLiability
/ us-gaap_BalanceSheetLocationAxis
= so_NetAmountOfDerivativesMember
/ us-gaap_DerivativeInstrumentRiskAxis
= us-gaap_EnergyRelatedDerivativeMember
/ dei_LegalEntityAxis
= so_MississippiPowerMember		 [1]
Net Amount Of Derivatives [Member] | Energy Related Derivative [Member] | Southern Power [Member]    
Derivative [Line Items]    
Derivative Asset, Fair Value, Gross Asset 5,500,000us-gaap_DerivativeFairValueOfDerivativeAsset
/ us-gaap_BalanceSheetLocationAxis
= so_NetAmountOfDerivativesMember
/ us-gaap_DerivativeInstrumentRiskAxis
= us-gaap_EnergyRelatedDerivativeMember
/ dei_LegalEntityAxis
= so_SouthernPowerMember		 [1] 600,000us-gaap_DerivativeFairValueOfDerivativeAsset
/ us-gaap_BalanceSheetLocationAxis
= so_NetAmountOfDerivativesMember
/ us-gaap_DerivativeInstrumentRiskAxis
= us-gaap_EnergyRelatedDerivativeMember
/ dei_LegalEntityAxis
= so_SouthernPowerMember		 [1]
Derivative Liability, Fair Value, Gross Liability 3,600,000us-gaap_DerivativeFairValueOfDerivativeLiability
/ us-gaap_BalanceSheetLocationAxis
= so_NetAmountOfDerivativesMember
/ us-gaap_DerivativeInstrumentRiskAxis
= us-gaap_EnergyRelatedDerivativeMember
/ dei_LegalEntityAxis
= so_SouthernPowerMember		 [1] 600,000us-gaap_DerivativeFairValueOfDerivativeLiability
/ us-gaap_BalanceSheetLocationAxis
= so_NetAmountOfDerivativesMember
/ us-gaap_DerivativeInstrumentRiskAxis
= us-gaap_EnergyRelatedDerivativeMember
/ dei_LegalEntityAxis
= so_SouthernPowerMember		 [1]
Net Amount Of Derivatives [Member] | Interest Rate Contract [Member]    
Derivative [Line Items]    
Derivative Asset, Fair Value, Gross Asset 8,000,000us-gaap_DerivativeFairValueOfDerivativeAsset
/ us-gaap_BalanceSheetLocationAxis
= so_NetAmountOfDerivativesMember
/ us-gaap_DerivativeInstrumentRiskAxis
= us-gaap_InterestRateContractMember		 [1] 3,000,000us-gaap_DerivativeFairValueOfDerivativeAsset
/ us-gaap_BalanceSheetLocationAxis
= so_NetAmountOfDerivativesMember
/ us-gaap_DerivativeInstrumentRiskAxis
= us-gaap_InterestRateContractMember		 [1]
Derivative Liability, Fair Value, Gross Liability 24,000,000us-gaap_DerivativeFairValueOfDerivativeLiability
/ us-gaap_BalanceSheetLocationAxis
= so_NetAmountOfDerivativesMember
/ us-gaap_DerivativeInstrumentRiskAxis
= us-gaap_InterestRateContractMember		 [1] 0us-gaap_DerivativeFairValueOfDerivativeLiability
/ us-gaap_BalanceSheetLocationAxis
= so_NetAmountOfDerivativesMember
/ us-gaap_DerivativeInstrumentRiskAxis
= us-gaap_InterestRateContractMember		 [1]
Net Amount Of Derivatives [Member] | Interest Rate Contract [Member] | Georgia Power [Member]    
Derivative [Line Items]    
Derivative Asset, Fair Value, Gross Asset 6,000,000us-gaap_DerivativeFairValueOfDerivativeAsset
/ us-gaap_BalanceSheetLocationAxis
= so_NetAmountOfDerivativesMember
/ us-gaap_DerivativeInstrumentRiskAxis
= us-gaap_InterestRateContractMember
/ dei_LegalEntityAxis
= so_GeorgiaPowerMember		 [1] 0us-gaap_DerivativeFairValueOfDerivativeAsset
/ us-gaap_BalanceSheetLocationAxis
= so_NetAmountOfDerivativesMember
/ us-gaap_DerivativeInstrumentRiskAxis
= us-gaap_InterestRateContractMember
/ dei_LegalEntityAxis
= so_GeorgiaPowerMember		 [1]
Derivative Liability, Fair Value, Gross Liability 14,000,000us-gaap_DerivativeFairValueOfDerivativeLiability
/ us-gaap_BalanceSheetLocationAxis
= so_NetAmountOfDerivativesMember
/ us-gaap_DerivativeInstrumentRiskAxis
= us-gaap_InterestRateContractMember
/ dei_LegalEntityAxis
= so_GeorgiaPowerMember		 [1] 0us-gaap_DerivativeFairValueOfDerivativeLiability
/ us-gaap_BalanceSheetLocationAxis
= so_NetAmountOfDerivativesMember
/ us-gaap_DerivativeInstrumentRiskAxis
= us-gaap_InterestRateContractMember
/ dei_LegalEntityAxis
= so_GeorgiaPowerMember		 [1]
Gross Amount Of Derivatives [Member] | Energy Related Derivative [Member]    
Derivative [Line Items]    
Derivative Asset, Fair Value, Amount Not Offset Against Collateral (9,000,000)us-gaap_DerivativeFairValueOfDerivativeAssetAmountNotOffsetAgainstCollateral
/ us-gaap_BalanceSheetLocationAxis
= so_GrossAmountOfDerivativesMember
/ us-gaap_DerivativeInstrumentRiskAxis
= us-gaap_EnergyRelatedDerivativeMember		 [2] (22,000,000)us-gaap_DerivativeFairValueOfDerivativeAssetAmountNotOffsetAgainstCollateral
/ us-gaap_BalanceSheetLocationAxis
= so_GrossAmountOfDerivativesMember
/ us-gaap_DerivativeInstrumentRiskAxis
= us-gaap_EnergyRelatedDerivativeMember		 [2]
Derivative Liability, Fair Value, Amount Not Offset Against Collateral (9,000,000)us-gaap_DerivativeFairValueOfDerivativeLiabilityAmountNotOffsetAgainstCollateral
/ us-gaap_BalanceSheetLocationAxis
= so_GrossAmountOfDerivativesMember
/ us-gaap_DerivativeInstrumentRiskAxis
= us-gaap_EnergyRelatedDerivativeMember		 [2] (22,000,000)us-gaap_DerivativeFairValueOfDerivativeLiabilityAmountNotOffsetAgainstCollateral
/ us-gaap_BalanceSheetLocationAxis
= so_GrossAmountOfDerivativesMember
/ us-gaap_DerivativeInstrumentRiskAxis
= us-gaap_EnergyRelatedDerivativeMember		 [2]
Gross Amount Of Derivatives [Member] | Energy Related Derivative [Member] | Alabama Power [Member]    
Derivative [Line Items]    
Derivative Asset, Fair Value, Amount Not Offset Against Collateral 0us-gaap_DerivativeFairValueOfDerivativeAssetAmountNotOffsetAgainstCollateral
/ us-gaap_BalanceSheetLocationAxis
= so_GrossAmountOfDerivativesMember
/ us-gaap_DerivativeInstrumentRiskAxis
= us-gaap_EnergyRelatedDerivativeMember
/ dei_LegalEntityAxis
= so_AlabamaPowerMember		 [2] (5,000,000)us-gaap_DerivativeFairValueOfDerivativeAssetAmountNotOffsetAgainstCollateral
/ us-gaap_BalanceSheetLocationAxis
= so_GrossAmountOfDerivativesMember
/ us-gaap_DerivativeInstrumentRiskAxis
= us-gaap_EnergyRelatedDerivativeMember
/ dei_LegalEntityAxis
= so_AlabamaPowerMember		 [2]
Derivative Liability, Fair Value, Amount Not Offset Against Collateral 0us-gaap_DerivativeFairValueOfDerivativeLiabilityAmountNotOffsetAgainstCollateral
/ us-gaap_BalanceSheetLocationAxis
= so_GrossAmountOfDerivativesMember
/ us-gaap_DerivativeInstrumentRiskAxis
= us-gaap_EnergyRelatedDerivativeMember
/ dei_LegalEntityAxis
= so_AlabamaPowerMember		 [2] (5,000,000)us-gaap_DerivativeFairValueOfDerivativeLiabilityAmountNotOffsetAgainstCollateral
/ us-gaap_BalanceSheetLocationAxis
= so_GrossAmountOfDerivativesMember
/ us-gaap_DerivativeInstrumentRiskAxis
= us-gaap_EnergyRelatedDerivativeMember
/ dei_LegalEntityAxis
= so_AlabamaPowerMember		 [2]
Gross Amount Of Derivatives [Member] | Energy Related Derivative [Member] | Georgia Power [Member]    
Derivative [Line Items]    
Derivative Asset, Fair Value, Amount Not Offset Against Collateral (7,000,000)us-gaap_DerivativeFairValueOfDerivativeAssetAmountNotOffsetAgainstCollateral
/ us-gaap_BalanceSheetLocationAxis
= so_GrossAmountOfDerivativesMember
/ us-gaap_DerivativeInstrumentRiskAxis
= us-gaap_EnergyRelatedDerivativeMember
/ dei_LegalEntityAxis
= so_GeorgiaPowerMember		 [2] (5,000,000)us-gaap_DerivativeFairValueOfDerivativeAssetAmountNotOffsetAgainstCollateral
/ us-gaap_BalanceSheetLocationAxis
= so_GrossAmountOfDerivativesMember
/ us-gaap_DerivativeInstrumentRiskAxis
= us-gaap_EnergyRelatedDerivativeMember
/ dei_LegalEntityAxis
= so_GeorgiaPowerMember		 [2]
Derivative Liability, Fair Value, Amount Not Offset Against Collateral (7,000,000)us-gaap_DerivativeFairValueOfDerivativeLiabilityAmountNotOffsetAgainstCollateral
/ us-gaap_BalanceSheetLocationAxis
= so_GrossAmountOfDerivativesMember
/ us-gaap_DerivativeInstrumentRiskAxis
= us-gaap_EnergyRelatedDerivativeMember
/ dei_LegalEntityAxis
= so_GeorgiaPowerMember		 [2] (5,000,000)us-gaap_DerivativeFairValueOfDerivativeLiabilityAmountNotOffsetAgainstCollateral
/ us-gaap_BalanceSheetLocationAxis
= so_GrossAmountOfDerivativesMember
/ us-gaap_DerivativeInstrumentRiskAxis
= us-gaap_EnergyRelatedDerivativeMember
/ dei_LegalEntityAxis
= so_GeorgiaPowerMember		 [2]
Gross Amount Of Derivatives [Member] | Energy Related Derivative [Member] | Gulf Power [Member]    
Derivative [Line Items]    
Derivative Asset, Fair Value, Amount Not Offset Against Collateral (123,000)us-gaap_DerivativeFairValueOfDerivativeAssetAmountNotOffsetAgainstCollateral
/ us-gaap_BalanceSheetLocationAxis
= so_GrossAmountOfDerivativesMember
/ us-gaap_DerivativeInstrumentRiskAxis
= us-gaap_EnergyRelatedDerivativeMember
/ dei_LegalEntityAxis
= so_GulfPowerMember		 [3] (5,775,000)us-gaap_DerivativeFairValueOfDerivativeAssetAmountNotOffsetAgainstCollateral
/ us-gaap_BalanceSheetLocationAxis
= so_GrossAmountOfDerivativesMember
/ us-gaap_DerivativeInstrumentRiskAxis
= us-gaap_EnergyRelatedDerivativeMember
/ dei_LegalEntityAxis
= so_GulfPowerMember		 [3]
Derivative Liability, Fair Value, Amount Not Offset Against Collateral (123,000)us-gaap_DerivativeFairValueOfDerivativeLiabilityAmountNotOffsetAgainstCollateral
/ us-gaap_BalanceSheetLocationAxis
= so_GrossAmountOfDerivativesMember
/ us-gaap_DerivativeInstrumentRiskAxis
= us-gaap_EnergyRelatedDerivativeMember
/ dei_LegalEntityAxis
= so_GulfPowerMember		 [3] (5,775,000)us-gaap_DerivativeFairValueOfDerivativeLiabilityAmountNotOffsetAgainstCollateral
/ us-gaap_BalanceSheetLocationAxis
= so_GrossAmountOfDerivativesMember
/ us-gaap_DerivativeInstrumentRiskAxis
= us-gaap_EnergyRelatedDerivativeMember
/ dei_LegalEntityAxis
= so_GulfPowerMember		 [3]
Gross Amount Of Derivatives [Member] | Energy Related Derivative [Member] | Mississippi Power [Member]    
Derivative [Line Items]    
Derivative Asset, Fair Value, Amount Not Offset Against Collateral (64,000)us-gaap_DerivativeFairValueOfDerivativeAssetAmountNotOffsetAgainstCollateral
/ us-gaap_BalanceSheetLocationAxis
= so_GrossAmountOfDerivativesMember
/ us-gaap_DerivativeInstrumentRiskAxis
= us-gaap_EnergyRelatedDerivativeMember
/ dei_LegalEntityAxis
= so_MississippiPowerMember		 [2] (3,856,000)us-gaap_DerivativeFairValueOfDerivativeAssetAmountNotOffsetAgainstCollateral
/ us-gaap_BalanceSheetLocationAxis
= so_GrossAmountOfDerivativesMember
/ us-gaap_DerivativeInstrumentRiskAxis
= us-gaap_EnergyRelatedDerivativeMember
/ dei_LegalEntityAxis
= so_MississippiPowerMember		 [2]
Derivative Liability, Fair Value, Amount Not Offset Against Collateral (64,000)us-gaap_DerivativeFairValueOfDerivativeLiabilityAmountNotOffsetAgainstCollateral
/ us-gaap_BalanceSheetLocationAxis
= so_GrossAmountOfDerivativesMember
/ us-gaap_DerivativeInstrumentRiskAxis
= us-gaap_EnergyRelatedDerivativeMember
/ dei_LegalEntityAxis
= so_MississippiPowerMember		 [2] (3,856,000)us-gaap_DerivativeFairValueOfDerivativeLiabilityAmountNotOffsetAgainstCollateral
/ us-gaap_BalanceSheetLocationAxis
= so_GrossAmountOfDerivativesMember
/ us-gaap_DerivativeInstrumentRiskAxis
= us-gaap_EnergyRelatedDerivativeMember
/ dei_LegalEntityAxis
= so_MississippiPowerMember		 [2]
Gross Amount Of Derivatives [Member] | Energy Related Derivative [Member] | Southern Power [Member]    
Derivative [Line Items]    
Derivative Asset, Fair Value, Amount Not Offset Against Collateral (100,000)us-gaap_DerivativeFairValueOfDerivativeAssetAmountNotOffsetAgainstCollateral
/ us-gaap_BalanceSheetLocationAxis
= so_GrossAmountOfDerivativesMember
/ us-gaap_DerivativeInstrumentRiskAxis
= us-gaap_EnergyRelatedDerivativeMember
/ dei_LegalEntityAxis
= so_SouthernPowerMember		 [2] (100,000)us-gaap_DerivativeFairValueOfDerivativeAssetAmountNotOffsetAgainstCollateral
/ us-gaap_BalanceSheetLocationAxis
= so_GrossAmountOfDerivativesMember
/ us-gaap_DerivativeInstrumentRiskAxis
= us-gaap_EnergyRelatedDerivativeMember
/ dei_LegalEntityAxis
= so_SouthernPowerMember		 [2]
Derivative Liability, Fair Value, Amount Not Offset Against Collateral (100,000)us-gaap_DerivativeFairValueOfDerivativeLiabilityAmountNotOffsetAgainstCollateral
/ us-gaap_BalanceSheetLocationAxis
= so_GrossAmountOfDerivativesMember
/ us-gaap_DerivativeInstrumentRiskAxis
= us-gaap_EnergyRelatedDerivativeMember
/ dei_LegalEntityAxis
= so_SouthernPowerMember		 [2] (100,000)us-gaap_DerivativeFairValueOfDerivativeLiabilityAmountNotOffsetAgainstCollateral
/ us-gaap_BalanceSheetLocationAxis
= so_GrossAmountOfDerivativesMember
/ us-gaap_DerivativeInstrumentRiskAxis
= us-gaap_EnergyRelatedDerivativeMember
/ dei_LegalEntityAxis
= so_SouthernPowerMember		 [2]
Gross Amount Of Derivatives [Member] | Interest Rate Contract [Member]    
Derivative [Line Items]    
Derivative Asset, Fair Value, Amount Not Offset Against Collateral (8,000,000)us-gaap_DerivativeFairValueOfDerivativeAssetAmountNotOffsetAgainstCollateral
/ us-gaap_BalanceSheetLocationAxis
= so_GrossAmountOfDerivativesMember
/ us-gaap_DerivativeInstrumentRiskAxis
= us-gaap_InterestRateContractMember		 [2] 0us-gaap_DerivativeFairValueOfDerivativeAssetAmountNotOffsetAgainstCollateral
/ us-gaap_BalanceSheetLocationAxis
= so_GrossAmountOfDerivativesMember
/ us-gaap_DerivativeInstrumentRiskAxis
= us-gaap_InterestRateContractMember		 [2]
Derivative Liability, Fair Value, Amount Not Offset Against Collateral (8,000,000)us-gaap_DerivativeFairValueOfDerivativeLiabilityAmountNotOffsetAgainstCollateral
/ us-gaap_BalanceSheetLocationAxis
= so_GrossAmountOfDerivativesMember
/ us-gaap_DerivativeInstrumentRiskAxis
= us-gaap_InterestRateContractMember		 [2] 0us-gaap_DerivativeFairValueOfDerivativeLiabilityAmountNotOffsetAgainstCollateral
/ us-gaap_BalanceSheetLocationAxis
= so_GrossAmountOfDerivativesMember
/ us-gaap_DerivativeInstrumentRiskAxis
= us-gaap_InterestRateContractMember		 [2]
Gross Amount Of Derivatives [Member] | Interest Rate Contract [Member] | Georgia Power [Member]    
Derivative [Line Items]    
Derivative Asset, Fair Value, Amount Not Offset Against Collateral (6,000,000)us-gaap_DerivativeFairValueOfDerivativeAssetAmountNotOffsetAgainstCollateral
/ us-gaap_BalanceSheetLocationAxis
= so_GrossAmountOfDerivativesMember
/ us-gaap_DerivativeInstrumentRiskAxis
= us-gaap_InterestRateContractMember
/ dei_LegalEntityAxis
= so_GeorgiaPowerMember		 [2] 0us-gaap_DerivativeFairValueOfDerivativeAssetAmountNotOffsetAgainstCollateral
/ us-gaap_BalanceSheetLocationAxis
= so_GrossAmountOfDerivativesMember
/ us-gaap_DerivativeInstrumentRiskAxis
= us-gaap_InterestRateContractMember
/ dei_LegalEntityAxis
= so_GeorgiaPowerMember		 [2]
Derivative Liability, Fair Value, Amount Not Offset Against Collateral $ (6,000,000)us-gaap_DerivativeFairValueOfDerivativeLiabilityAmountNotOffsetAgainstCollateral
/ us-gaap_BalanceSheetLocationAxis
= so_GrossAmountOfDerivativesMember
/ us-gaap_DerivativeInstrumentRiskAxis
= us-gaap_InterestRateContractMember
/ dei_LegalEntityAxis
= so_GeorgiaPowerMember		 [2] $ 0us-gaap_DerivativeFairValueOfDerivativeLiabilityAmountNotOffsetAgainstCollateral
/ us-gaap_BalanceSheetLocationAxis
= so_GrossAmountOfDerivativesMember
/ us-gaap_DerivativeInstrumentRiskAxis
= us-gaap_InterestRateContractMember
/ dei_LegalEntityAxis
= so_GeorgiaPowerMember		 [2]
[1] The Company does not offset fair value amounts for multiple derivative instruments executed with the same counterparty on the balance sheets; therefore, gross and net amounts of derivative assets and liabilities presented on the balance sheets are the same.
[2] Includes gross amounts subject to netting terms that are not offset on the balance sheets and any cash/financial collateral pledged or received.
[3] (b)Includes gross amounts subject to netting terms that are not offset on the balance sheets and any cash/financial collateral pledged or received.