<DefinitionAndReference>
  <Element Id="us-gaap_Assets">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_DebtInstrumentInterestRateStatedPercentage">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_ProceedsFromPaymentsForOtherFinancingActivities">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_CommitmentsDisclosureTextBlock">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="so_WholesaleRevenues">
    <definition>Revenues from sales of energy supplied by one producer or marketer to another for eventual resale to consumers.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_IncreaseDecreaseInAccruedSalaries">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_OtherComprehensiveIncomeUnrealizedGainLossOnDerivativesArisingDuringPeriodNetOfTax">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_PensionAndOtherPostretirementDefinedBenefitPlansLiabilitiesNoncurrent">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_OtherLongTermDebt">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_RepaymentsOfLongTermDebtAndCapitalSecurities">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="so_LongTermDebtMaturitiesRepaymentsOfPrincipalInLastTwelveMonths">
    <definition>Amount of long-term debt matured in the past twelve months
following the date of the latest balance sheet presented in the
financial statements, which may include maturities of longterm
debt, sinking fund requirements, and other securities
redeemable at fixed or detereminable prices and dates.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_UtilitiesOperatingExpenseMaintenanceAndOperations">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_JuniorSubordinatedDebentureOwedToUnconsolidatedSubsidiaryTrust">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_DerivativeInstrumentsAndHedgesLiabilities">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_OtherNonoperatingIncomeExpense">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_ConstructionInProgressGross">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_AccountsReceivableGrossCurrent">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_DebtDisclosureTextBlock">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_TreasuryStockShares">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="so_NuclearFuelAtAmortizedCost">
    <definition>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.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_OtherComprehensiveIncomeReclassificationOfDefinedBenefitPlansNetGainLossRecognizedInNetPeriodicBenefitCostNetOfTax">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_AccumulatedOtherComprehensiveIncomeLossNetOfTax">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_ProceedsFromMinorityShareholders">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_LongTermDebtMaturitiesRepaymentsOfPrincipalInNextTwelveMonths">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="so_IncreaseDecreaseInAccruedTaxes">
    <definition>The net change during the period in the amount of cash payments due to taxing authorities for income and nonincome-related taxes.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_OtherInventorySupplies">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_OtherComprehensiveIncomeReclassificationAdjustmentForSaleOfSecuritiesIncludedInNetIncomeTax">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_IncomeTaxExpenseBenefit">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_DebtInstrumentUnamortizedDiscountPremiumNet">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_CumulativeEffectOfInitialAdoptionOfNewAccountingPrinciple">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_IncreaseDecreaseInOtherOperatingLiabilities">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_OtherLongTermInvestments">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_StockholdersEquityOther">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_OtherComprehensiveIncomeUnrealizedHoldingGainLossOnSecuritiesArisingDuringPeriodTax">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_ScheduleOfJointlyOwnedUtilityPlantsTextBlock">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_TemporaryEquityCarryingAmount">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="dei_EntityVoluntaryFilers">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_AssetRetirementObligationsNoncurrent">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_GainLossOnContractTermination">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_CustomerDepositsCurrent">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="so_PreferredStockDividendRateStatedPercentageRateRangeMaximum">
    <definition>Preferred Stock Dividend Rate Stated Percentage Rate Range Maximum.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_AdjustmentsNoncashItemsToReconcileNetIncomeLossToCashProvidedByUsedInOperatingActivitiesOther">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="dei_EntityPublicFloat">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_PensionAndOtherPostretirementBenefitsDisclosureTextBlock">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="dei_DocumentPeriodEndDate">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="dei_EntityCentralIndexKey">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_GainsLossesOnExtinguishmentOfDebtBeforeWriteOffOfDeferredDebtIssuanceCost">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_ComprehensiveIncomeNetOfTaxIncludingPortionAttributableToNoncontrollingInterest">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="so_VacationPay">
    <definition>Carrying amount at the balance sheet date of the regulatory asset related to vacation pay to employees.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_OtherComprehensiveIncomeDefinedBenefitPlansNetUnamortizedGainLossArisingDuringPeriodTax">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="so_RetailRevenues">
    <definition>Revenues from sales of electric energy to retail regulated customers.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_FairValueDisclosuresTextBlock">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_CashAndCashEquivalentsAtCarryingValue">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="dei_EntityCurrentReportingStatus">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="so_IncomeLossFromContinuingOperationsBeforeIncomeTaxesAndMinorityInterest">
    <definition>Sum of operating profit and nonoperating income (expense) before income taxes, extraordinary items, cumulative effects of changes in accounting principles, and noncontrolling interest.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_AccountsPayableCurrent">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_WeightedAverageNumberOfSharesOutstandingBasic">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_LiabilitiesCurrent">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_IncreaseDecreaseInRawMaterialsPackagingMaterialsAndSuppliesInventories">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_NetIncomeLossAttributableToNoncontrollingInterest">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="dei_EntityFilerCategory">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="so_MinorityInterestInPercentOfTotalCapitalization">
    <definition>As a percent of total capitalization, the total of all Stockholders' Equity (deficit) items, net of receivables from officers, directors owners, and affiliates of the entity which is directly or indirectly attributable to that ownership interest in subsidiary equity which is not attributable to the parent (noncontrolling interest, minority interest).</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_InvestmentIncomeInterestAndDividend">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="so_ChangeInConstructionPayables">
    <definition>The net change during the reporting period in the aggregate amount of construction obligations due within one year (or one business cycle). This includes accounts payable related to construction activities.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_SharesIssued">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_PrepaidExpenseCurrent">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="so_TotalCommonStockholdersEquityInPercentOfTotalCapitalization">
    <definition>As a percent of total capitalization, the total of all Common Stockholders' Equity (deficit) items, net of receivables from officers, directors owners, and affiliates of the entity. This excludes temporary equity and preferred and preference stockholders' equity.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_TreasuryStockValue">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_LeveragedLeasesBalanceSheetInvestmentInLeveragedLeasesNet">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_AccruedIncomeTaxesCurrent">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="dei_CurrentFiscalYearEndDate">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_PensionAndOtherPostretirementBenefitExpense">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_PropertyPlantAndEquipmentGross">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_CommitmentsAndContingencies2009">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_AccruedVacationCurrent">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_EnergyRelatedInventoryOtherFossilFuel">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_IncreaseDecreaseInReceivables">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_NetCashProvidedByUsedInFinancingActivities">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_TreasuryStockSharesAcquired">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_LongTermDebtMaturitiesRepaymentsOfPrincipalInYearFour">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="so_LongTermDebtAndCapitalLeaseObligationsInPercentOfTotalCapitalization">
    <definition>As a percent of total capitalization, the sum of the carrying values as of the balance sheet date of all long-term debt, which is debt initially having maturities due after one year from the balance sheet date or beyond the operating cycle, if longer, but excluding the portions thereof scheduled to be repaid within one year or the normal operating cycle, if longer plus capital lease obligations due to be paid more than one year after the balance sheet date.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_OtherComprehensiveIncomeReclassificationOfDefinedBenefitPlansNetGainLossRecognizedInNetPeriodicBenefitCostTax">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="so_AnnualizedInterestLongTermDebt">
    <definition>Represents the interest expected to be incurred during the next twelve months on long-term debt.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_OtherAssetsCurrent">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_SignificantAccountingPoliciesTextBlock">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_CommonStockValue">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_Revenues">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_NetCashProvidedByUsedInOperatingActivities">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="so_OtherRegulatoryLiabilitiesDeferred">
    <definition>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.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_NonoperatingIncomeExpense">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_DecommissioningFundInvestments">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_StockIssuedDuringPeriodValueNewIssues">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_OtherComprehensiveIncomeReclassificationAdjustmentOnDerivativesIncludedInNetIncomeNetOfTax">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_IncomeLossFromEquityMethodInvestments">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="so_TotalLongTermSeniorNotesAndDebt">
    <definition>Including the current and noncurrent portions, carrying value as of the balance sheet date of Long-term Notes and Other Long-term Debt with the highest claim on the assets of the issuer in case of bankruptcy or liquidation (with maturities initially due after one year or beyond the operating cycle if longer). Senior note holders are paid off in full before any payments are made to junior note holders.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_IncreaseDecreaseInAccountsPayable">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_OtherLiabilitiesCurrent">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_StockholdersEquityIncludingPortionAttributableToNoncontrollingInterest">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="so_TotalCapitalizationInPercent">
    <definition>Total Capitalization in Percent.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_LiabilitiesAndStockholdersEquity">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="so_PreferredStockDividendRateStatedPercentageRateRangeMinimum">
    <definition>Preferred Stock Dividend Rate Stated Percentage Rate Range Minimum.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_CommonStockParOrStatedValuePerShare">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_PaymentsToAcquirePropertyPlantAndEquipment">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_ProceedsFromDistributionOfRestrictedCashFromPollutionControlBond">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_AllowanceForDoubtfulAccountsReceivableCurrent">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="so_PlantInServiceNetOfDepreciation">
    <definition>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.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_ScheduleOfValuationAndQualifyingAccountsDisclosureTextBlock">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_PaymentsForRepurchaseOfRedeemablePreferredStock">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_PaymentsOfDividendsCommonStock">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_IncreaseDecreaseInOtherOperatingAssets">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_LongTermDebtMaturitiesRepaymentsOfPrincipalInYearTwo">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_ProceedsFromIssuanceOfLongTermDebtAndCapitalSecuritiesNet">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="so_AllowanceForEquityFundsUsedDuringConstruction">
    <definition>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.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_DebtInstrumentInterestRateStatedPercentageRateRangeMinimum">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="so_UnderRecoveredRegulatoryClauseRevenues">
    <definition>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.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="so_OtherRegulatoryAssetsCurrent">
    <definition>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.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="so_TemporaryEquityCarryingAmountInPercentOfTotalCapitalization">
    <definition>As a percent of total capitalization, the carrying value (book value) of an entity's issued and outstanding stock which is not included within permanent equity in Stockholders Equity. Temporary equity is a security with redemption features that are outside the control of the issuer, is not classified as an asset or liability in conformity with GAAP, and is not mandatorily redeemable. Includes any type of security that is redeemable at a fixed or determinable price or on a fixed or determinable date or dates, is redeemable at the option of the holder, or has conditions for redemption which are not solely within the control of the issuer. If convertible, the issuer does not control the actions or events necessary to issue the maximum number of shares that could be required to be delivered under the conversion option if the holder exercises the option to convert the stock to another class of equity. If the security is a warrant or a rights issue, the warrant or rights issue is considered to be temporary equity if the issuer cannot demonstrate that it would be able to deliver upon the exercise of the option by the holder in all cases. Includes stock with a put option held by an ESOP and stock redeemable by a holder only in the event of a change in control of the issuer.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_RecognitionOfDeferredRevenue">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_ProfitLoss">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_PreferredStockParOrStatedValuePerShare">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_InterestAndDebtExpense">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_StockIssuedDuringPeriodSharesNewIssues">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_CapitalizationLongtermDebtAndEquity">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_RedeemablePreferredStockSharesAuthorized">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_OtherComprehensiveIncomeDefinedBenefitPlanNetPriorServiceCostsArisingDuringPeriodTax">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_DerivativeInstrumentsAndHedgingActivitiesDisclosureTextBlock">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="so_CommonStockTextBlock">
    <definition>Disclosures related to common stock issued, common stock reserved,
non-qualified stock option plans, diluted earnings per share, and common stock dividend restrictions.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_LongTermInvestments">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_DeferredTaxLiabilitiesNoncurrent">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_EarningsPerShareDiluted">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="dei_AmendmentFlag">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_Liabilities">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_CostsAndExpenses">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_UtilitiesOperatingExpenseFuelUsed">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_PreferredStockSharesAuthorized">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="so_ContingenciesAndRegulatoryMattersTextBlock">
    <definition>Contingencies and Regulatory Matters.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="so_HedgeSettlements">
    <definition>The cash outflow (inflow) for a financial contract that settles in the period relating to operating activities.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_OtherComprehensiveIncomeUnrealizedGainLossOnDerivativesArisingDuringPeriodTax">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_LongTermDebtMaturitiesRepaymentsOfPrincipalAfterYearFive">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="so_LongTermDebtAndCapitalLeaseObligationNetTotal">
    <definition>Sum of the carrying values as of the balance sheet date of all long-term debt, which is debt initially having maturities due after one year from the balance sheet date or beyond the operating cycle, if longer, plus capital lease obligations.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_DepreciationAmortizationAndAccretionNet">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_OperatingIncomeLoss">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_OtherComprehensiveIncomeReclassificationAdjustmentForSaleOfSecuritiesIncludedInNetIncomeNetOfTax">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_RestrictedCashAndInvestmentsCurrent">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="so_DeferredCreditsRelatedToIncomeTaxes">
    <definition>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.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_PaymentsForProceedsFromOtherInvestingActivities">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_AccrualForTaxesOtherThanIncomeTaxesCurrent">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="so_OtherElectricRevenues">
    <definition>Other operating revenues of electric companies not elsewhere specified in the taxonomy.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_CapitalLeaseObligations">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="so_TotalDeferredCreditsAndOtherLiabilities">
    <definition>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.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_LongTermDebtMaturitiesRepaymentsOfPrincipalInYearThree">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="so_NuclearInsuranceTextBlock">
    <definition>Disclosures related to insurance pertaining to nuclear facilities.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="so_OtherCostOfRemovalObligations">
    <definition>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."</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="so_OtherRegulatoryAssetsDeferred">
    <definition>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.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_OtherSalesRevenueNet">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_LongTermDebtMaturitiesRepaymentsOfPrincipalInYearFive">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_TaxesExcludingIncomeAndExciseTaxes">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_SegmentReportingDisclosureTextBlock">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_WeightedAverageNumberOfDilutedSharesOutstanding">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_DebtInstrumentInterestRateStatedPercentageRateRangeMaximum">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_LongTermDebtAndCapitalLeaseObligationsCurrent">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_PropertyPlantAndEquipmentNet">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_PaymentsToInvestInDecommissioningFund">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="so_TotalCommonStockholdersEquity">
    <definition>Total of all Common Stockholders' Equity (deficit) items, net of receivables from officers, directors, owners, and affiliates of the entity. This excludes temporary equity and preferred and preference stockholders' equity.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="so_UnbilledRevenuesCurrent">
    <definition>Carrying amount at the balance sheet date of revenues which have been earned but not yet billed.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="dei_DocumentType">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_AccumulatedDeferredInvestmentTaxCredit">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_ShortTermBorrowings">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="so_OtherAccountsNotesAndLoansReceivable">
    <definition>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.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_AdditionalPaidInCapitalCommonStock">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_OtherLiabilitiesNoncurrent">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_AssetsCurrent">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_PaymentsForInvestmentInRestrictedCashFromPollutionControlBond">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_UnamortizedLossReacquiredDebtNoncurrent">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="so_OtherRegulatoryLiabilitiesCurrent">
    <definition>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.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_LongtermPollutionControlBondCurrentAndNoncurrent">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="so_UnrecognizedTaxBenefitsAccruedTaxes">
    <definition>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.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_IncomeTaxDisclosureTextBlock">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_CommonStockSharesAuthorized">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="so_TotalDeferredChargesAndOtherAssets">
    <definition>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.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_ProceedsFromSaleOfProductiveAssets">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="so_DepreciationAndAmortizationExcludingNuclearFuel">
    <definition>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.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_InterestPayableCurrent">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="so_DeferredChargesRelatedToIncomeTaxes">
    <definition>Noncurrent regulatory assets associated with deferred income tax liabilities that are expected to be recovered from customers through the ratemaking process.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_IncreaseDecreaseInFossilFuelInventories">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_OtherComprehensiveIncomeReclassificationAdjustmentOnDerivativesIncludedInNetIncomeTax">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_StockOptionPlanExpense">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_OtherComprehensiveIncomeUnrealizedHoldingGainLossOnSecuritiesArisingDuringPeriodNetOfTax">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_ProceedsFromRepaymentsOfShortTermDebt">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_AccruedSalariesCurrent">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_LeveragedLeasesIncomeStatementNetIncomeFromLeveragedLeases">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_ProceedsFromDecommissioningFund">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_OtherAssetsNoncurrent">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_CommonStockSharesIssued">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_PaymentsForProceedsFromRemovalCosts">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_DividendsCommonStockCash">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_CommonStockDividendsPerShareCashPaid">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_LongTermDebtAndCapitalLeaseObligations">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_NetCashProvidedByUsedInInvestingActivities">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="dei_EntityRegistrantName">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_CostOfPurchasedPower">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_NetIncomeLossAvailableToCommonStockholdersBasic">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_PaymentsOfDividendsMinorityInterest">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_QuarterlyFinancialInformationTextBlock">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="so_DeferredUnderRecoveredRegulatoryClauseRevenues">
    <definition>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.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_PreferredStockSharesOutstanding">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="dei_EntityWellKnownSeasonedIssuer">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_MinorityInterest">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_RetainedEarningsAccumulatedDeficit">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_AccumulatedDepreciationDepletionAndAmortizationPropertyPlantAndEquipment">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="so_AnnualDividendPreferredAndPreferenceStock">
    <definition>Represents the dividend expected to be paid during the next twelve months to preferred and/or preference stockholders.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_OtherComprehensiveIncomeLossNetOfTaxPortionAttributableToParent">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_OtherComprehensiveIncomeDefinedBenefitPlansNetUnamortizedGainLossArisingDuringPeriodNetOfTax">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_OtherComprehensiveIncomeDefinedBenefitPlanNetPriorServiceCostsCreditArisingDuringPeriodNetOfTax">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_RedeemablePreferredStockSharesOutstanding">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_DeferredIncomeTaxExpenseBenefit">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_EarningsPerShareBasic">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="dei_EntityCommonStockSharesOutstanding">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_CashAndCashEquivalentsPeriodIncreaseDecrease">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_ProceedsFromIssuanceOfCommonStock">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_UnamortizedDebtIssuanceExpense">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_GainLossRelatedToLitigationSettlement">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
</DefinitionAndReference>
