1.0.0.3 false Consolidated Balance Sheets (USD $) In Millions false 1 $ false false Pure Standard http://www.xbrl.org/2003/instance pure xbrli 0 Shares Standard http://www.xbrl.org/2003/instance shares xbrli 0 USD Standard http://www.xbrl.org/2003/iso4217 USD iso4217 0 false 2 $ false false Pure Standard http://www.xbrl.org/2003/instance pure xbrli 0 Shares Standard http://www.xbrl.org/2003/instance shares xbrli 0 USD Standard http://www.xbrl.org/2003/iso4217 USD iso4217 0 4 Current Assets: 2 us-gaap_AssetsCurrentAbstract us-gaap true na duration string No definition available. false false false false false true false false false 1 false false 0 0 false false 2 false false 0 0 false false No definition available. false 5 Cash and cash equivalents 3 us-gaap_CashAndCashEquivalentsAtCarryingValue us-gaap true debit instant monetary No definition available. false false false false false false false false false 1 true true 690000000 690 false false 2 true true 417000000 417 false false No definition available. No authoritative reference available. false 6 Restricted cash and cash equivalents 3 us-gaap_RestrictedCashAndInvestmentsCurrent us-gaap true debit instant monetary No definition available. false false false false false false false false false 1 false true 43000000 43 false false 2 false true 103000000 103 false false No definition available. No authoritative reference available. false 7 Receivables - 3 us-gaap_ReceivablesNetCurrentAbstract us-gaap true na duration string No definition available. false false false false false true false false false 1 false false 0 0 false false 2 false false 0 0 false false No definition available. false 8 Customer accounts receivable 4 us-gaap_AccountsReceivableGrossCurrent us-gaap true debit instant monetary No definition available. false false false false false false false false false 1 false true 953000000 953 false false 2 false true 1054000000 1054 false false No definition available. No authoritative reference available. false 9 Unbilled revenues 4 so_UnbilledRevenuesCurrent so false debit instant monetary Carrying amount at the balance sheet date of revenues which have been earned but not yet billed. false false false false false false false false false 1 false true 394000000 394 false false 2 false true 320000000 320 false false Carrying amount at the balance sheet date of revenues which have been earned but not yet billed. No authoritative reference available. false 10 Under recovered regulatory clause revenues 4 so_UnderRecoveredRegulatoryClauseRevenues so false debit instant monetary Carrying amount at the balance sheet date of customer accounts receivable for retail and wholesale under recovered fuel... false false false false false false false false false 1 false true 333000000 333 false false 2 false true 646000000 646 false false Carrying amount at the balance sheet date of customer accounts receivable for retail and wholesale under recovered fuel costs, and other under recovered regulatory costs. No authoritative reference available. false 11 Other accounts and notes receivable 4 so_OtherAccountsNotesAndLoansReceivable so false debit instant monetary Amounts due from customers or clients, within one year of the balance sheet date (or one operating cycle, if longer), for... false false false false false false false false false 1 false true 375000000 375 false false 2 false true 301000000 301 false false Amounts due from customers or clients, within one year of the balance sheet date (or one operating cycle, if longer), for goods or services that have been delivered or sold in the normal course of business and an amount representing an agreement for an unconditional promise by the maker to pay the entity (holder) a definite sum of money at a future date within one year of the balance sheet, not elsewhere specified in the taxonomy. No authoritative reference available. false 12 Accumulated provision for uncollectible accounts 4 us-gaap_AllowanceForDoubtfulAccountsReceivableCurrent us-gaap true credit instant monetary No definition available. false false false false false false false false false 1 false true -25000000 -25 false false 2 false true -26000000 -26 false false No definition available. No authoritative reference available. false 13 Fossil fuel stock, at average cost 3 us-gaap_EnergyRelatedInventoryOtherFossilFuel us-gaap true debit instant monetary No definition available. false false false false false false false false false 1 false true 1447000000 1447 false false 2 false true 1018000000 1018 false false No definition available. No authoritative reference available. false 14 Materials and supplies, at average cost 3 us-gaap_OtherInventorySupplies us-gaap true debit instant monetary No definition available. false false false false false false false false false 1 false true 794000000 794 false false 2 false true 757000000 757 false false No definition available. No authoritative reference available. false 15 Vacation pay 3 so_VacationPay so false debit instant monetary Carrying amount at the balance sheet date of the regulatory asset related to vacation pay to employees. false false false false false false false false false 1 false true 145000000 145 false false 2 false true 140000000 140 false false Carrying amount at the balance sheet date of the regulatory asset related to vacation pay to employees. No authoritative reference available. false 16 Prepaid expenses 3 us-gaap_PrepaidExpenseCurrent us-gaap true debit instant monetary No definition available. false false false false false false false false false 1 false true 508000000 508 false false 2 false true 302000000 302 false false No definition available. No authoritative reference available. false 17 Other regulatory assets, current 3 so_OtherRegulatoryAssetsCurrent so false debit instant monetary Carrying amount of other regulatory assets (not elsewhere included) as of the balance sheet date of capitalized costs of... false false false false false false false false false 1 false true 167000000 167 false false 2 false true 275000000 275 false false Carrying amount of other regulatory assets (not elsewhere included) as of the balance sheet date of capitalized costs of regulated entities that are expected to be recovered through revenue sources within one year or the normal operating cycle, if longer. Such costs are capitalized if they meet both of the following criteria: a. It is probable that future revenue in an amount at least equal to the capitalized cost will result from inclusion of that cost in allowable costs for rate-making purposes. b. Based on available evidence, the future revenue will be provided to permit recovery of the previously incurred cost rather than to provide for expected levels of similar future costs. If the revenue will be provided through an automatic rate-adjustment clause, this criterion requires that the regulator's intent clearly be to permit recovery of the previously incurred cost. No authoritative reference available. false 18 Other current assets 3 us-gaap_OtherAssetsCurrent us-gaap true debit instant monetary No definition available. false false false false false false false false false 1 false true 49000000 49 false false 2 false true 51000000 51 false false No definition available. No authoritative reference available. true 19 Total current assets 3 us-gaap_AssetsCurrent us-gaap true debit instant monetary No definition available. false false false false false false false false false 1 false true 5873000000 5873 false false 2 false true 5358000000 5358 false false No definition available. No authoritative reference available. true 20 Property, Plant, and Equipment: 2 us-gaap_PropertyPlantAndEquipmentNetAbstract us-gaap true na duration string No definition available. false false false false false true false false false 1 false false 0 0 false false 2 false false 0 0 false false No definition available. false 21 In service 3 us-gaap_PropertyPlantAndEquipmentGross us-gaap true debit instant monetary No definition available. false false false false false false false false false 1 false true 53588000000 53588 false false 2 false true 50618000000 50618 false false No definition available. No authoritative reference available. false 22 Less accumulated depreciation 3 us-gaap_AccumulatedDepreciationDepletionAndAmortizationPropertyPlantAndEquipment us-gaap true credit instant monetary No definition available. false false false false false false false false false 1 false true 19121000000 19121 false false 2 false true 18286000000 18286 false false No definition available. No authoritative reference available. true 23 Plant in service, net of depreciation 3 so_PlantInServiceNetOfDepreciation so false debit instant monetary Carrying amount at the balance sheet date for long-lived physical assets used in the normal conduct of business and not... false false false false false false false false false 1 false true 34467000000 34467 false false 2 false true 32332000000 32332 false false Carrying amount at the balance sheet date for long-lived physical assets used in the normal conduct of business and not intended for resale, less depreciation. No authoritative reference available. false 24 Nuclear fuel, at amortized cost 3 so_NuclearFuelAtAmortizedCost so false debit instant monetary The carrying amount as of the balance sheet of nuclear fuel held as property plant and equipment. This amount is net of... false false false false false false false false false 1 false true 593000000 593 false false 2 false true 510000000 510 false false The carrying amount as of the balance sheet of nuclear fuel held as property plant and equipment. This amount is net of amortization based on the energy produced over the life of the fuel. No authoritative reference available. false 25 Construction work in progress 3 us-gaap_ConstructionInProgressGross us-gaap true debit instant monetary No definition available. false false false false false false false false false 1 false true 4170000000 4170 false false 2 false true 3036000000 3036 false false No definition available. No authoritative reference available. true 26 Total property, plant, and equipment 3 us-gaap_PropertyPlantAndEquipmentNet us-gaap true debit instant monetary No definition available. false false false false false false false false false 1 false true 39230000000 39230 false false 2 false true 35878000000 35878 false false No definition available. No authoritative reference available. true 27 Other Property and Investments: 2 us-gaap_LongTermInvestmentsAbstract us-gaap true na duration string No definition available. false false false false false true false false false 1 false false 0 0 false false 2 false false 0 0 false false No definition available. false 28 Nuclear decommissioning trusts, at fair value 3 us-gaap_DecommissioningFundInvestments us-gaap true debit instant monetary No definition available. false false false false false false false false false 1 false true 1070000000 1070 false false 2 false true 864000000 864 false false No definition available. No authoritative reference available. false 29 Leveraged leases 3 us-gaap_LeveragedLeasesBalanceSheetInvestmentInLeveragedLeasesNet us-gaap true debit instant monetary No definition available. false false false false false false false false false 1 false true 610000000 610 false false 2 false true 897000000 897 false false No definition available. No authoritative reference available. false 30 Miscellaneous property and investments 3 us-gaap_OtherLongTermInvestments us-gaap true debit instant monetary No definition available. false false false false false false false false false 1 false true 283000000 283 false false 2 false true 227000000 227 false false No definition available. No authoritative reference available. true 31 Total other property and investments 3 us-gaap_LongTermInvestments us-gaap true debit instant monetary No definition available. false false false false false false false false false 1 false true 1963000000 1963 false false 2 false true 1988000000 1988 false false No definition available. No authoritative reference available. true 32 Deferred Charges and Other Assets: 2 so_DeferredChargesAndOtherAssetsAbstract so false na duration string Deferred Charges and Other Assets. false false false false false true false false false 1 false false 0 0 false false 2 false false 0 0 false false Deferred Charges and Other Assets. false 33 Deferred charges related to income taxes 3 so_DeferredChargesRelatedToIncomeTaxes so false debit instant monetary Noncurrent regulatory assets associated with deferred income tax liabilities that are expected to be recovered from customers... false false false false false false false false false 1 false true 1047000000 1047 false false 2 false true 973000000 973 false false Noncurrent regulatory assets associated with deferred income tax liabilities that are expected to be recovered from customers through the ratemaking process. No authoritative reference available. false 34 Unamortized debt issuance expense 3 us-gaap_UnamortizedDebtIssuanceExpense us-gaap true debit instant monetary No definition available. false false false false false false false false false 1 false true 208000000 208 false false 2 false true 208000000 208 false false No definition available. No authoritative reference available. false 35 Unamortized loss on reacquired debt 3 us-gaap_UnamortizedLossReacquiredDebtNoncurrent us-gaap true debit instant monetary No definition available. false false false false false false false false false 1 false true 255000000 255 false false 2 false true 271000000 271 false false No definition available. No authoritative reference available. false 36 Deferred under recovered regulatory clause revenues 3 so_DeferredUnderRecoveredRegulatoryClauseRevenues so false debit instant monetary Carrying amount at the balance sheet date of underrecovered fuel costs allowed to be deferred by regulatory authorities, that... false false false false false false false false false 1 false true 373000000 373 false false 2 false true 606000000 606 false false Carrying amount at the balance sheet date of underrecovered fuel costs allowed to be deferred by regulatory authorities, that are expected to be recoverable through rate adjustments after one year. No authoritative reference available. false 37 Other regulatory assets, deferred 3 so_OtherRegulatoryAssetsDeferred so false debit instant monetary Carrying amount of other regulatory assets (not elsewhere identified) as of the balance sheet date of capitalized costs of... false false false false false false false false false 1 false true 2702000000 2702 false false 2 false true 2636000000 2636 false false Carrying amount of other regulatory assets (not elsewhere identified) as of the balance sheet date of capitalized costs of regulated entities that are not expected to be recovered through revenue sources within one year or the normal operating cycle if longer. No authoritative reference available. false 38 Other deferred charges and assets 3 us-gaap_OtherAssetsNoncurrent us-gaap true debit instant monetary No definition available. false false false false false false false false false 1 false true 395000000 395 false false 2 false true 429000000 429 false false No definition available. No authoritative reference available. true 39 Total deferred charges and other assets 3 so_TotalDeferredChargesAndOtherAssets so false debit instant monetary Sum of the carrying amounts as of the balance sheet date of all assets, excluding Property, Plant, and Equipment and Other... false false false false false false false false false 1 false true 4980000000 4980 false false 2 false true 5123000000 5123 false false Sum of the carrying amounts as of the balance sheet date of all assets, excluding Property, Plant, and Equipment and Other Property and Investments, that are expected to be realized in cash, sold or consumed after one year or beyond the normal operating cycle, if longer. No authoritative reference available. true 40 Total Assets 2 us-gaap_Assets us-gaap true debit instant monetary No definition available. false false false false false false false false false 1 false true 52046000000 52046 false false 2 false true 48347000000 48347 false false No definition available. No authoritative reference available. true 42 Current Liabilities: 2 us-gaap_LiabilitiesCurrentAbstract us-gaap true na duration string No definition available. false false false false false true false false false 1 false false 0 0 false false 2 false false 0 0 false false No definition available. false 43 Securities due within one year 3 us-gaap_LongTermDebtAndCapitalLeaseObligationsCurrent us-gaap true credit instant monetary No definition available. false false false false false false false false false 1 false true 1113000000 1113 false false 2 false true 617000000 617 false false No definition available. No authoritative reference available. false 44 Notes payable 3 us-gaap_ShortTermBorrowings us-gaap true credit instant monetary No definition available. false false false false false false false false false 1 false true 639000000 639 false false 2 false true 953000000 953 false false No definition available. No authoritative reference available. false 45 Accounts payable 3 us-gaap_AccountsPayableCurrent us-gaap true credit instant monetary No definition available. false false false false false false false false false 1 false true 1329000000 1329 false false 2 false true 1250000000 1250 false false No definition available. No authoritative reference available. false 46 Customer deposits 3 us-gaap_CustomerDepositsCurrent us-gaap true credit instant monetary No definition available. false false false false false false false false false 1 false true 331000000 331 false false 2 false true 302000000 302 false false No definition available. No authoritative reference available. false 47 Accrued taxes - 3 us-gaap_TaxesPayableCurrentAbstract us-gaap true na duration string No definition available. false false false false false true false false false 1 false false 0 0 false false 2 false false 0 0 false false No definition available. false 48 Accrued income taxes 4 us-gaap_AccruedIncomeTaxesCurrent us-gaap true credit instant monetary No definition available. false false false false false false false false false 1 false true 13000000 13 false false 2 false true 197000000 197 false false No definition available. No authoritative reference available. false 49 Unrecognized tax benefits 4 so_UnrecognizedTaxBenefitsAccruedTaxes so false credit instant monetary Liability associated with tax benefits that do not currently fully meet the "more likely than not" threshold as defined by... false false false false false false false false false 1 false true 166000000 166 false false 2 false true 131000000 131 false false Liability associated with tax benefits that do not currently fully meet the "more likely than not" threshold as defined by FIN 48. This line item includes both federal and state taxes. No authoritative reference available. false 50 Other accrued taxes 4 us-gaap_AccrualForTaxesOtherThanIncomeTaxesCurrent us-gaap true credit instant monetary No definition available. false false false false false false false false false 1 false true 398000000 398 false false 2 false true 396000000 396 false false No definition available. No authoritative reference available. false 51 Accrued interest 3 us-gaap_InterestPayableCurrent us-gaap true credit instant monetary No definition available. false false false false false false false false false 1 false true 218000000 218 false false 2 false true 196000000 196 false false No definition available. No authoritative reference available. false 52 Accrued vacation pay 3 us-gaap_AccruedVacationCurrent us-gaap true credit instant monetary No definition available. false false false false false false false false false 1 false true 184000000 184 false false 2 false true 179000000 179 false false No definition available. No authoritative reference available. false 53 Accrued compensation 3 us-gaap_AccruedSalariesCurrent us-gaap true credit instant monetary No definition available. false false false false false false false false false 1 false true 248000000 248 false false 2 false true 447000000 447 false false No definition available. No authoritative reference available. false 54 Liabilities from risk management activities 3 us-gaap_DerivativeInstrumentsAndHedgesLiabilities us-gaap true credit instant monetary No definition available. false false false false false false false false false 1 false true 125000000 125 false false 2 false true 261000000 261 false false No definition available. No authoritative reference available. false 55 Other regulatory liabilities, current 3 so_OtherRegulatoryLiabilitiesCurrent so false credit instant monetary The amount for other current regulatory liabilities not elsewhere included. Regulatory liabilities represent probable future... false false false false false false false false false 1 false true 528000000 528 false false 2 false true 78000000 78 false false The amount for other current regulatory liabilities not elsewhere included. Regulatory liabilities represent probable future reductions in revenues associated with amounts that are expected to be credited to customers through the ratemaking process. These revenues are expected to be credited within one year. No authoritative reference available. false 56 Other current liabilities 3 us-gaap_OtherLiabilitiesCurrent us-gaap true credit instant monetary No definition available. false false false false false false false false false 1 false true 292000000 292 false false 2 false true 219000000 219 false false No definition available. No authoritative reference available. true 57 Total current liabilities 3 us-gaap_LiabilitiesCurrent us-gaap true credit instant monetary No definition available. false false false false false false false false false 1 false true 5584000000 5584 false false 2 false true 5226000000 5226 false false No definition available. No authoritative reference available. true 58 Long-Term Debt (See accompanying statements) 2 us-gaap_LongTermDebtAndCapitalLeaseObligations us-gaap true credit instant monetary No definition available. false false false false false false false false false 1 false true 18131000000 18131 false false 2 false true 16816000000 16816 false false No definition available. No authoritative reference available. true 59 Deferred Credits and Other Liabilities: 2 so_DeferredCreditsAndOtherLiabilitiesAbstract so false na duration string Deferred Credits and Other Liabilities. false false false false false true false false false 1 false false 0 0 false false 2 false false 0 0 false false Deferred Credits and Other Liabilities. false 60 Accumulated deferred income taxes 3 us-gaap_DeferredTaxLiabilitiesNoncurrent us-gaap true credit instant monetary No definition available. false false false false false false false false false 1 false true 6455000000 6455 false false 2 false true 6080000000 6080 false false No definition available. No authoritative reference available. false 61 Deferred credits related to income taxes 3 so_DeferredCreditsRelatedToIncomeTaxes so false credit instant monetary Noncurrent regulatory liabilities associated with deferred income tax liabilities. Regulatory liabilities represent probable... false false false false false false false false false 1 false true 248000000 248 false false 2 false true 259000000 259 false false Noncurrent regulatory liabilities associated with deferred income tax liabilities. Regulatory liabilities represent probable future reductions in revenues associated with amounts that are expected to be credited to customers through the ratemaking process. These revenues are not expected to be credited within one year or the normal operating cycle if longer. No authoritative reference available. false 62 Accumulated deferred investment tax credits 3 us-gaap_AccumulatedDeferredInvestmentTaxCredit us-gaap true credit instant monetary No definition available. false false false false false false false false false 1 false true 448000000 448 false false 2 false true 455000000 455 false false No definition available. No authoritative reference available. false 63 Employee benefit obligations 3 us-gaap_PensionAndOtherPostretirementDefinedBenefitPlansLiabilitiesNoncurrent us-gaap true credit instant monetary No definition available. false false false false false false false false false 1 false true 2304000000 2304 false false 2 false true 2057000000 2057 false false No definition available. No authoritative reference available. false 64 Asset retirement obligations 3 us-gaap_AssetRetirementObligationsNoncurrent us-gaap true credit instant monetary No definition available. false false false false false false false false false 1 false true 1201000000 1201 false false 2 false true 1183000000 1183 false false No definition available. No authoritative reference available. false 65 Other cost of removal obligations 3 so_OtherCostOfRemovalObligations so false credit instant monetary The regulatory liability as of the balance sheet date for the amount recovered from ratepayers for removal costs associated... false false false false false false false false false 1 false true 1091000000 1091 false false 2 false true 1321000000 1321 false false The regulatory liability as of the balance sheet date for the amount recovered from ratepayers for removal costs associated with utility plant in service which are not recognized as a liability under Statement of Financial Accounting Standards No. 143, "Accounting for Asset Retirement Obligations" and FASB Interpretation No. 47, "Accounting for Conditional Asset Retirement Obligations." No authoritative reference available. false 66 Other regulatory liabilities, deferred 3 so_OtherRegulatoryLiabilitiesDeferred so false credit instant monetary The amount for other noncurrent regulatory liabilities not elsewhere included. Regulatory liabilities represent probable... false false false false false false false false false 1 false true 278000000 278 false false 2 false true 262000000 262 false false The amount for other noncurrent regulatory liabilities not elsewhere included. Regulatory liabilities represent probable future reductions in revenues associated with amounts that are expected to be credited to customers through the ratemaking process. These revenues are not expected to be credited within one year or the normal operating cycle if longer. No authoritative reference available. false 67 Other deferred credits and liabilities 3 us-gaap_OtherLiabilitiesNoncurrent us-gaap true credit instant monetary No definition available. false false false false false false false false false 1 false true 346000000 346 false false 2 false true 330000000 330 false false No definition available. No authoritative reference available. true 68 Total deferred credits and other liabilities 3 so_TotalDeferredCreditsAndOtherLiabilities so false credit instant monetary Total obligations, excluding Long-term Debt, incurred as part of normal operations that is expected to be repaid beyond the... false false false false false false false false false 1 false true 12371000000 12371 false false 2 false true 11947000000 11947 false false Total obligations, excluding Long-term Debt, incurred as part of normal operations that is expected to be repaid beyond the following twelve months or one business cycle. No authoritative reference available. true 69 Total Liabilities 2 us-gaap_Liabilities us-gaap true credit instant monetary No definition available. false false false false false false false false false 1 false true 36086000000 36086 false false 2 false true 33989000000 33989 false false No definition available. No authoritative reference available. true 70 Redeemable Preferred Stock of Subsidiaries (See accompanying statements) 2 us-gaap_TemporaryEquityCarryingAmount us-gaap true credit instant monetary No definition available. false false false false false false false false false 1 false true 375000000 375 false false 2 false true 375000000 375 false false No definition available. No authoritative reference available. true 71 Total Stockholders' Equity (See accompanying statements) 2 us-gaap_StockholdersEquityIncludingPortionAttributableToNoncontrollingInterest us-gaap true credit instant monetary No definition available. false false false false false false false false false 1 false true 15585000000 15585 false false 2 false true 13983000000 13983 false false No definition available. No authoritative reference available. true 72 Total Liabilities and Stockholders' Equity 2 us-gaap_LiabilitiesAndStockholdersEquity us-gaap true credit instant monetary No definition available. false false false false false false false false false 1 true true 52046000000 52046 false false 2 true true 48347000000 48347 false false No definition available. No authoritative reference available. true false 2 68 false Millions UnKnown UnKnown false true