1.0.0.3 false Consolidated Statements of Income (USD $) In Millions, except Per Share data false 1 $ false false Shares Standard http://www.xbrl.org/2003/instance shares xbrli 0 USD Standard http://www.xbrl.org/2003/iso4217 USD iso4217 0 USDEPS Divide http://www.xbrl.org/2003/iso4217 USD iso4217 http://www.xbrl.org/2003/instance shares xbrli 0 false 2 $ false false Shares Standard http://www.xbrl.org/2003/instance shares xbrli 0 USD Standard http://www.xbrl.org/2003/iso4217 USD iso4217 0 USDEPS Divide http://www.xbrl.org/2003/iso4217 USD iso4217 http://www.xbrl.org/2003/instance shares xbrli 0 false 3 $ false false Shares Standard http://www.xbrl.org/2003/instance shares xbrli 0 USD Standard http://www.xbrl.org/2003/iso4217 USD iso4217 0 USDEPS Divide http://www.xbrl.org/2003/iso4217 USD iso4217 http://www.xbrl.org/2003/instance shares xbrli 0 3 Operating Revenues: 1 us-gaap_RevenuesAbstract 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 3 false false 0 0 false false No definition available. false 4 Retail revenues 2 so_RetailRevenues so false credit duration monetary Revenues from sales of electric energy to retail regulated customers. false false false false false false false false false 1 true true 13307000000 13307 false false 2 true true 14055000000 14055 false false 3 true true 12639000000 12639 false false Revenues from sales of electric energy to retail regulated customers. No authoritative reference available. false 5 Wholesale revenues 2 so_WholesaleRevenues so false credit duration monetary Revenues from sales of energy supplied by one producer or marketer to another for eventual resale to consumers. false false false false false false false false false 1 false true 1802000000 1802 false false 2 false true 2400000000 2400 false false 3 false true 1988000000 1988 false false Revenues from sales of energy supplied by one producer or marketer to another for eventual resale to consumers. No authoritative reference available. false 6 Other electric revenues 2 so_OtherElectricRevenues so false credit duration monetary Other operating revenues of electric companies not elsewhere specified in the taxonomy. false false false false false false false false false 1 false true 533000000 533 false false 2 false true 545000000 545 false false 3 false true 513000000 513 false false Other operating revenues of electric companies not elsewhere specified in the taxonomy. No authoritative reference available. false 7 Other revenues 2 us-gaap_OtherSalesRevenueNet us-gaap true credit duration monetary No definition available. false false false false false false false false false 1 false true 101000000 101 false false 2 false true 127000000 127 false false 3 false true 213000000 213 false false No definition available. No authoritative reference available. true 8 Total operating revenues 2 us-gaap_Revenues us-gaap true credit duration monetary No definition available. false false false false false false false false false 1 false true 15743000000 15743 false false 2 false true 17127000000 17127 false false 3 false true 15353000000 15353 false false No definition available. No authoritative reference available. true 9 Operating Expenses: 1 us-gaap_CostsAndExpensesAbstract 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 3 false false 0 0 false false No definition available. false 10 Fuel 2 us-gaap_UtilitiesOperatingExpenseFuelUsed us-gaap true debit duration monetary No definition available. false false false false false false false false false 1 false true 5952000000 5952 false false 2 false true 6818000000 6818 false false 3 false true 5856000000 5856 false false No definition available. No authoritative reference available. false 11 Purchased power 2 us-gaap_CostOfPurchasedPower us-gaap true debit duration monetary No definition available. false false false false false false false false false 1 false true 474000000 474 false false 2 false true 815000000 815 false false 3 false true 515000000 515 false false No definition available. No authoritative reference available. false 12 Other operations and maintenance 2 us-gaap_UtilitiesOperatingExpenseMaintenanceAndOperations us-gaap true debit duration monetary No definition available. false false false false false false false false false 1 false true 3526000000 3526 false false 2 false true 3748000000 3748 false false 3 false true 3670000000 3670 false false No definition available. No authoritative reference available. false 13 MC Asset Recovery litigation settlement 2 us-gaap_GainLossRelatedToLitigationSettlement us-gaap true credit duration monetary No definition available. false false false false false false false false false 1 false true 202000000 202 false false 2 false true 0 0 false false 3 false true 0 0 false false No definition available. No authoritative reference available. false 14 Depreciation and amortization 2 so_DepreciationAndAmortizationExcludingNuclearFuel so false debit duration monetary The current period expense charged against earnings on long-lived, physical assets used in the normal conduct of business and... false false false false false false false false false 1 false true 1503000000 1503 false false 2 false true 1443000000 1443 false false 3 false true 1245000000 1245 false false The current period expense charged against earnings on long-lived, physical assets used in the normal conduct of business and not intended for resale to allocate or recognize the cost of assets over their useful lives; or to record the reduction in book value of an intangible asset over the benefit period of such asset. Excludes amortization of nuclear fuel. No authoritative reference available. false 15 Taxes other than income taxes 2 us-gaap_TaxesExcludingIncomeAndExciseTaxes us-gaap true debit duration monetary No definition available. false false false false false false false false false 1 false true 818000000 818 false false 2 false true 797000000 797 false false 3 false true 741000000 741 false false No definition available. No authoritative reference available. true 16 Total operating expenses 2 us-gaap_CostsAndExpenses us-gaap true debit duration monetary No definition available. false false false false false false false false false 1 false true 12475000000 12475 false false 2 false true 13621000000 13621 false false 3 false true 12027000000 12027 false false No definition available. No authoritative reference available. true 17 Operating Income 1 us-gaap_OperatingIncomeLoss us-gaap true credit duration monetary No definition available. false false false false false false false false false 1 false true 3268000000 3268 false false 2 false true 3506000000 3506 false false 3 false true 3326000000 3326 false false No definition available. No authoritative reference available. false 18 Other Income and (Expense): 1 us-gaap_NonoperatingIncomeExpenseAbstract 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 3 false false 0 0 false false No definition available. false 19 Allowance for equity funds used during construction 2 so_AllowanceForEquityFundsUsedDuringConstruction so false credit duration monetary Total increase in earnings in the period representing the cost of equity (rate of return) used to finance construction of... false false false false false false false false false 1 false true 200000000 200 false false 2 false true 152000000 152 false false 3 false true 106000000 106 false false Total increase in earnings in the period representing the cost of equity (rate of return) used to finance construction of regulated assets, which is expected to be recovered through rate adjustments. No authoritative reference available. false 20 Interest income 2 us-gaap_InvestmentIncomeInterestAndDividend us-gaap true credit duration monetary No definition available. false false false false false false false false false 1 false true 23000000 23 false false 2 false true 33000000 33 false false 3 false true 45000000 45 false false No definition available. No authoritative reference available. false 21 Equity in (losses) income of unconsolidated subsidiaries 2 us-gaap_IncomeLossFromEquityMethodInvestments us-gaap true credit duration monetary No definition available. false false false false false false false false false 1 false true -1000000 -1 false false 2 false true 11000000 11 false false 3 false true -24000000 -24 false false No definition available. No authoritative reference available. false 22 Leveraged lease income (losses) 2 us-gaap_LeveragedLeasesIncomeStatementNetIncomeFromLeveragedLeases us-gaap true credit duration monetary No definition available. false false false false false false false false false 1 false true 31000000 31 false false 2 false true -85000000 -85 false false 3 false true 40000000 40 false false No definition available. No authoritative reference available. false 23 Gain on disposition of lease termination 2 us-gaap_GainLossOnContractTermination us-gaap true credit duration monetary No definition available. false false false false false false false false false 1 false true 26000000 26 false false 2 false true 0 0 false false 3 false true 0 0 false false No definition available. No authoritative reference available. false 24 Loss on extinguishment of debt 2 us-gaap_GainsLossesOnExtinguishmentOfDebtBeforeWriteOffOfDeferredDebtIssuanceCost us-gaap true credit duration monetary No definition available. false false false false false false false false false 1 false true -17000000 -17 false false 2 false true 0 0 false false 3 false true 0 0 false false No definition available. No authoritative reference available. false 25 Interest expense, net of amounts capitalized 2 us-gaap_InterestAndDebtExpense us-gaap true debit duration monetary No definition available. false false false false false false false false false 1 false true -905000000 -905 false false 2 false true -866000000 -866 false false 3 false true -886000000 -886 false false No definition available. No authoritative reference available. false 26 Other income (expense), net 2 us-gaap_OtherNonoperatingIncomeExpense us-gaap true credit duration monetary No definition available. false false false false false false false false false 1 false true -21000000 -21 false false 2 false true -29000000 -29 false false 3 false true 10000000 10 false false No definition available. No authoritative reference available. true 27 Total other income and (expense) 2 us-gaap_NonoperatingIncomeExpense us-gaap true credit duration monetary No definition available. false false false false false false false false false 1 false true -664000000 -664 false false 2 false true -784000000 -784 false false 3 false true -709000000 -709 false false No definition available. No authoritative reference available. true 28 Earnings Before Income Taxes 1 so_IncomeLossFromContinuingOperationsBeforeIncomeTaxesAndMinorityInterest so false credit duration monetary Sum of operating profit and nonoperating income (expense) before income taxes, extraordinary items, cumulative effects of... false false false false false false false false false 1 false true 2604000000 2604 false false 2 false true 2722000000 2722 false false 3 false true 2617000000 2617 false false Sum of operating profit and nonoperating income (expense) before income taxes, extraordinary items, cumulative effects of changes in accounting principles, and noncontrolling interest. No authoritative reference available. false 29 Income taxes 1 us-gaap_IncomeTaxExpenseBenefit us-gaap true debit duration monetary No definition available. false false false false false false false false false 1 false true 896000000 896 false false 2 false true 915000000 915 false false 3 false true 835000000 835 false false No definition available. No authoritative reference available. true 30 Consolidated Net Income 1 us-gaap_ProfitLoss us-gaap true credit duration monetary No definition available. false false false false false false false false false 1 false true 1708000000 1708 false false 2 false true 1807000000 1807 false false 3 false true 1782000000 1782 false false No definition available. No authoritative reference available. false 31 Dividends on Preferred and Preference Stock of Subsidiaries 1 us-gaap_NetIncomeLossAttributableToNoncontrollingInterest us-gaap true debit duration monetary No definition available. false false false false false false false false false 1 false true 65000000 65 false false 2 false true 65000000 65 false false 3 false true 48000000 48 false false No definition available. No authoritative reference available. true 32 Consolidated Net Income After Dividends on Preferred and Preference Stock of Subsidiaries 1 us-gaap_NetIncomeLossAvailableToCommonStockholdersBasic us-gaap true credit duration monetary No definition available. false false false false false false false false false 1 true true 1643000000 1643 false false 2 true true 1742000000 1742 false false 3 true true 1734000000 1734 false false No definition available. No authoritative reference available. true 34 Earnings per share (EPS) - 2 us-gaap_EarningsPerShareAbstract 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 3 false false 0 0 false false No definition available. false 35 Basic EPS 3 us-gaap_EarningsPerShareBasic us-gaap true na duration decimal No definition available. false false false false false false false false true 1 true true 2.07 2.07 false false 2 true true 2.26 2.26 false false 3 true true 2.29 2.29 false false No definition available. No authoritative reference available. false 36 Diluted EPS 3 us-gaap_EarningsPerShareDiluted us-gaap true na duration decimal No definition available. false false false false false false false false true 1 true true 2.06 2.06 false false 2 true true 2.25 2.25 false false 3 true true 2.28 2.28 false false No definition available. No authoritative reference available. true 37 Average number of shares of common stock outstanding - (in millions) 2 us-gaap_WeightedAverageNumberOfSharesOutstandingAbstract 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 3 false false 0 0 false false No definition available. false 38 Basic 3 us-gaap_WeightedAverageNumberOfSharesOutstandingBasic us-gaap true na duration shares No definition available. false false false false false false false false false 1 false true 795000000 795 false false 2 false true 771000000 771 false false 3 false true 756000000 756 false false No definition available. No authoritative reference available. false 39 Diluted 3 us-gaap_WeightedAverageNumberOfDilutedSharesOutstanding us-gaap true na duration shares No definition available. false false false false false false false false false 1 false true 796000000 796 false false 2 false true 775000000 775 false false 3 false true 761000000 761 false false No definition available. No authoritative reference available. true 40 Cash dividends paid per share of common stock 2 us-gaap_CommonStockDividendsPerShareCashPaid us-gaap true na duration decimal No definition available. false false false false false false false false true 1 true true 1.7325 1.7325 false false 2 true true 1.6625 1.6625 false false 3 true true 1.595 1.595 false false No definition available. No authoritative reference available. true false 3 37 false Millions Millions NoRounding false true