2.0.0.10 false Condensed Consolidated Statements of Income (Unaudited) (USD $) 0110 - Statement - Condensed Consolidated Statements of Income (Unaudited) true false In Thousands, except Per Share data false false 1 usd $ 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 usd $ 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 false false verboselabel false 1 false false false false 0 0 false false false 2 false false false false 0 0 false 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 false false verboselabel false 1 true true false false 3458920000 3458920 false false false 2 true true false false 3064659000 3064659 false 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 false false verboselabel false 1 false true false false 541587000 541587 false false false 2 false true false false 451414000 451414 false 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 false false verboselabel false 1 false true false false 135435000 135435 false false false 2 false true false false 122798000 122798 false 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 false false totallabel false 1 false true false false 21375000 21375 false false false 2 false true false false 27436000 27436 false false false Revenues from the sale of other goods or rendering of other services, not elsewhere specified in the taxonomy; net of (reduced by) sales adjustments, returns, allowances, and discounts. Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Regulation S-X (SX) -Number 210 -Section 03 -Paragraph 1 -Article 5 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 false false totallabel false 1 false true false false 4157317000 4157317 false false false 2 false true false false 3666307000 3666307 false false false Aggregate revenue recognized during the period (derived from goods sold, services rendered, insurance premiums, or other activities that constitute an entity's earning process). For financial services companies, also includes investment and interest income, and sales and trading gains. Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Regulation S-X (SX) -Number 210 -Section 03 -Paragraph 1 -Article 5 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 false false verboselabel false 1 false false false false 0 0 false false false 2 false false false false 0 0 false 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 false false verboselabel false 1 false true false false 1645158000 1645158 false false false 2 false true false false 1406267000 1406267 false false false The amount of fuel used charged against earnings for the period. 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 false false verboselabel false 1 false true false false 126566000 126566 false false false 2 false true false false 107644000 107644 false false false Cost of electricity purchased and sold during the reporting period. 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 false false verboselabel false 1 false true false false 908024000 908024 false false false 2 false true false false 871081000 871081 false false false Discloses the amount of operating expense for the period for routine plant maintenance, repairs and operations. 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 false true negated false 1 false false false false 0 0 false false false 2 false true false false 202000000 202000 false false false The net proceeds or assets obtained in excess of (less than) the net carrying amount of assets recorded, or assets distributed and liabilities assumed less than (in excess of) litigation reserves extinguished, in settlement of a litigation matter. Represents (for other than an insurance entity in its normal claims settlement process), the amount of income (expense) recognized in the period to settle pending or threatened litigation and insurance claims. Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Statement of Financial Accounting Standard (FAS) -Number 5 -Paragraph 9, 10, 11, 12 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 false false verboselabel false 1 false true false false 343380000 343380 false false false 2 false true false false 389758000 389758 false 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 false false totallabel false 1 false true false false 212195000 212195 false false false 2 false true false false 199880000 199880 false false false All taxes not related to income of the entity or excise or sales taxes levied on the revenue of the entity that are not reported elsewhere. These taxes could include production, real estate, personal property, and pump tax. 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 false false totallabel false 1 false true false false 3235323000 3235323 false false false 2 false true false false 3176630000 3176630 false false false Total costs of sales and operating expenses for the period. 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 false false verboselabel false 1 false true false false 921994000 921994 false false false 2 false true false false 489677000 489677 false false false The net result for the period of deducting operating expenses from operating revenues. 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 false false verboselabel false 1 false false false false 0 0 false false false 2 false false false false 0 0 false 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 false false verboselabel false 1 false true false false 49391000 49391 false false false 2 false true false false 42612000 42612 false 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 false false verboselabel false 1 false true false false 4787000 4787 false false false 2 false true false false 6908000 6908 false false false Income derived from investments in debt and equity securities and on cash and cash equivalents. Interest income represents earnings which reflect the time value of money or transactions in which the payments are for the use or forbearance of money. Dividend income represents a distribution of earnings to shareholders by investee companies. Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Statement of Financial Accounting Standard (FAS) -Number 115 -Paragraph 14 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Regulation S-X (SX) -Number 210 -Section 03 -Paragraph 7 -Subparagraph a, b -Article 5 false 21 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 false false verboselabel false 1 false true false false 6131000 6131 false false false 2 false true false false 9441000 9441 false false false The total recognized during the period for income on leases meeting the criteria for classification as leveraged leases. Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Statement of Financial Accounting Standard (FAS) -Number 13 -Paragraph 47 false 22 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 false true negated false 1 false true false false -222482000 -222482 false false false 2 false true false false -225727000 -225727 false false false Interest and debt related expenses associated with nonoperating financing activities of the entity. Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Statement of Financial Accounting Standard (FAS) -Number 34 -Paragraph 21 false 23 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 false false totallabel false 1 false true false false -13437000 -13437 false false false 2 false true false false -13826000 -13826 false false false The net amount of other nonoperating income and expense, which does not qualify for separate disclosure on the income statement under materiality guidelines. Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Regulation S-X (SX) -Number 210 -Section 03 -Paragraph 9 -Article 5 true 24 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 false false totallabel false 1 false true false false -175610000 -175610 false false false 2 false true false false -180592000 -180592 false false false The aggregate amount of income (expense) from ancillary business-related activities (that is to say, excluding major activities considered part of the normal operations of the business). Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Regulation S-X (SX) -Number 210 -Section 03 -Paragraph 7 -Article 5 true 25 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 false false verboselabel false 1 false true false false 746384000 746384 false false false 2 false true false false 309085000 309085 false 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 26 Income taxes 1 us-gaap_IncomeTaxExpenseBenefit us-gaap true debit duration monetary No definition available. false false false false false false false false false false false totallabel false 1 false true false false 235681000 235681 false false false 2 false true false false 167169000 167169 false false false The sum of the current income tax expense (benefit) and the deferred income tax expense (benefit) pertaining to continuing operations. Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Regulation S-X (SX) -Number 210 -Section 08 -Paragraph h -Article 4 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Statement of Financial Accounting Standard (FAS) -Number 109 -Paragraph 45 -Subparagraph a, b true 27 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 false false terselabel false 1 false true false false 510703000 510703 false false false 2 false true false false 141916000 141916 false false false The consolidated profit or loss for the period, net of income taxes, including the portion attributable to the noncontrolling interest. Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher AICPA -Name Accounting Research Bulletin (ARB) -Number 51 -Paragraph A1, A4, A5 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher AICPA -Name Accounting Research Bulletin (ARB) -Number 51 -Paragraph 5 -Subparagraph b Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher AICPA -Name Accounting Research Bulletin (ARB) -Number 51 -Paragraph 29 Reference 4: http://www.xbrl.org/2003/role/presentationRef -Publisher AICPA -Name Accounting Research Bulletin (ARB) -Number 51 -Paragraph 38 -Subparagraph a Reference 5: http://www.xbrl.org/2003/role/presentationRef -Publisher AICPA -Name Accounting Research Bulletin (ARB) -Number 51 -Paragraph 38 -Subparagraph c(1) false 28 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 false false totallabel false 1 false true false false 16195000 16195 false false false 2 false true false false 16195000 16195 false false false The portion of net income (loss) attributable to the noncontrolling interest (if any) deducted in order to derive the portion attributable to the parent. Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher AICPA -Name Accounting Research Bulletin (ARB) -Number 51 -Paragraph 38 -Subparagraph a Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher AICPA -Name Accounting Research Bulletin (ARB) -Number 51 -Paragraph 38 -Subparagraph c(1) Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher AICPA -Name Accounting Research Bulletin (ARB) -Number 51 -Paragraph A1, A4, A5 true 29 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 false false totallabel false 1 true true false false 494508000 494508 false false false 2 true true false false 125721000 125721 false false false Net income after adjustments for dividends on preferred stock (declared in the period) and/or cumulative preferred stock (accumulated for the period). Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Statement of Financial Accounting Standard (FAS) -Number 128 -Paragraph 9 true 31 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 false false verboselabel false 1 false false false false 0 0 false false false 2 false false false false 0 0 false false false No definition available. false 32 Basic EPS 3 us-gaap_EarningsPerShareBasic us-gaap true na duration decimal No definition available. false false false false false false false false false false false verboselabel true 1 true true false false 0.6 0.6 false false false 2 true true false false 0.16 0.16 false false false The amount of net income or loss for the period per each share of common stock outstanding during the reporting period. Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Regulation S-X (SX) -Number 210 -Section 04 -Paragraph 21 -Article 9 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Statement of Financial Accounting Standard (FAS) -Number 128 -Paragraph 36, 37, 38 Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Regulation S-X (SX) -Number 210 -Section 03 -Paragraph 20 -Article 5 Reference 4: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Regulation S-X (SX) -Number 210 -Section 04 -Paragraph 18 -Article 7 false 33 Diluted EPS 3 us-gaap_EarningsPerShareDiluted us-gaap true na duration decimal No definition available. false false false false false false false false false false false verboselabel true 1 true true false false 0.6 0.6 false false false 2 true true false false 0.16 0.16 false false false The amount of net income or loss for the period per each share of common stock and dilutive common stock equivalents outstanding during the reporting period. Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Statement of Financial Accounting Standard (FAS) -Number 128 -Paragraph 11, 12, 36 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Regulation S-X (SX) -Number 210 -Section 03 -Paragraph 20 -Article 5 Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Regulation S-X (SX) -Number 210 -Section 04 -Paragraph 18 -Article 7 Reference 4: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Regulation S-X (SX) -Number 210 -Section 04 -Paragraph 21 -Article 9 false 34 Average number of shares of common stock outstanding (in thousands) 2 us-gaap_WeightedAverageNumberOfSharesOutstandingAbstract us-gaap true na duration string No definition available. false false false false false true false false false false false verboselabel false 1 false false false false 0 0 false false false 2 false false false false 0 0 false false false No definition available. false 35 Basic 3 us-gaap_WeightedAverageNumberOfSharesOutstandingBasic us-gaap true na duration shares No definition available. false false false false false false false false false false false verboselabel false 1 false true false false 822526000 822526 false false false 2 false true false false 779858000 779858 false false false Number of [basic] shares, after adjustment for contingently issuable shares and other shares not deemed outstanding, determined by relating the portion of time within a reporting period that common shares have been outstanding to the total time in that period. Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Statement of Financial Accounting Standard (FAS) -Number 128 -Paragraph 171 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Statement of Financial Accounting Standard (FAS) -Number 128 -Paragraph 40 -Subparagraph a Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Statement of Financial Accounting Standard (FAS) -Number 128 -Paragraph 8 false 36 Diluted 3 us-gaap_WeightedAverageNumberOfDilutedSharesOutstanding us-gaap true na duration shares No definition available. false false false false false false false false false false false verboselabel false 1 false true false false 824787000 824787 false false false 2 false true false false 781645000 781645 false false false The average number of shares issued and outstanding that are used in calculating diluted EPS, determined based on the timing of issuance of shares in the period. Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Statement of Financial Accounting Standard (FAS) -Number 128 -Paragraph 40 -Subparagraph a Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Statement of Financial Accounting Standard (FAS) -Number 128 -Paragraph 8 false 37 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 false false false verboselabel true 1 true true false false 0.4375 0.4375 false false false 2 true true false false 0.42 0.42 false false false Aggregate dividends paid during the period for each share of common stock outstanding. Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Regulation S-X (SX) -Number 210 -Section 04 -Article 3 false false 2 34 false Thousands Thousands NoRounding false true