<DefinitionAndReference>
  <Element Id="so_CivilPenaltiesUnderCleanAirActPerDayUpperRangeLimit">
    <definition>Civil penalties under clean Air Act per day, upper range.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="so_AmountsRelatedToDefinedBenefitPensionPlansThatHadNotYetBeenRecognizedInNetPeriodicPensionCostAlongWithEstimatedAmortizationTextBlock">
    <definition>Amounts Related  To Defined Benefit Pension Plans That Had Not Yet Been Recognized In Net Periodic Pension Cost Along With Estimated Amortization.</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="so_CurrentBillingRatesUnderRateEcrInTermsOfPerUnits">
    <definition>Current Billing Rates under Rate ECR in terms of per units.</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="us-gaap_OtherNonoperatingIncomeExpense">
    <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="us-gaap_DebtInstrumentFairValue">
    <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_ExpectedVolumeOfNaturalGasSubjectToOptionToSellBackExcessGasDueToOperationalConstraints">
    <definition>Expected volume of natural gas subject to option to sell back excess gas due to operational constraints</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_DefinedBenefitPlanBenefitsPaid">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_DeferredFederalIncomeTaxExpenseBenefit">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingNumber">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_DecommissioningTrustAssetsAmount">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="so_RetailReturnOnEquityRangeMaximum">
    <definition>Retail Return On Equity Range Maximum.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="so_PortionOfPartnersAssetInAssetsLeasedBySubsidiaryCompany">
    <definition>Portion of partners asset in assets leased by the subsidiary company.</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="us-gaap_UnrecognizedTaxBenefitsDecreasesResultingFromSettlementsWithTaxingAuthorities">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_DefinedBenefitPlanInterestCost">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="so_AccumulatedProvisionsForDecommissioningTotal">
    <definition>Accumulated Provisions For Decommissioning Total.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="so_FutureStatedRatesUnderRateEcrFactorInTermsOfPerUnits">
    <definition>Future Stated Rates under Rate ECR factor in terms of per units.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_InterestPaidNet">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="so_ApproximateAnnualReductionInCnpRateDueToExpirationOfPpa">
    <definition>Approximate Annual Reduction in CNP rate due to the expirationof the PPA.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="so_ApplicableUSFederalStatutoryRateToEarningsBeforeIncomeTaxesAndPreferredAndPreferenceDividendsOfSubsidiariesTextBlock">
    <definition>Applicable U.S. federal statutory rate to earnings before income taxes and preferred and preference dividends of subsidiaries.</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="us-gaap_IncreaseDecreaseInOtherOperatingLiabilities">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_DefinedBenefitPlanEquitySecurities">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="so_EffectiveIncomeTaxRateReconciliationLitigationSettlement">
    <definition>Effective income tax rate reconciliation due to litigation settlement.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="so_RecoveryAndAmortizationPeriodsForRegulatoryAssetsLiabilitiesApprovedByPscs">
    <definition>Recovery and amortization periods for regulatory assets (liabilities), approved by PSCs.</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_LongtermPollutionControlBondCurrentAndNoncurrent">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="so_AggregatePaymentForClaimsResultingFromTerroristActsInOneYearPeriod">
    <definition>Aggregate payment for claims resulting from terrorist acts in one year period.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="so_ApprovedIncreaseInTotalAnnualBillingBasedOnFuelCostRecoveryRate">
    <definition>Approved Increase In Total Annual Billing Based On Fuel Cost Recovery Rate.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_ScheduleOfVariableInterestEntitiesTextBlock">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="so_MaximumLimitsForAccidentalPropertyDamageOccurringDuringConstruction">
    <definition>Maximum Limits For Accidental Property Damage Occurring During Construction.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="so_ComponentsOfOtherComprehensiveIncomeAlongWithChangesInBalanceOfRegulatoryAssetsRelatedToOtherPostretirementBenefitPlansTextBlock">
    <definition>Components of other comprehensive income along with changes in balance of regulatory assets related to other postretirement benefit plans.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="so_DeferredStateTaxAssets">
    <definition>Deferred state tax assets.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_PrescriptionDrugSubsidyReceiptsYearThree">
    <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_DefinedBenefitPlanExpectedFutureBenefitPaymentsInYearTwo">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="so_LeveragedLeaseAgreementsWithTermsRanging">
    <definition>Leveraged Lease Agreements With Terms Ranging.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsExercisesInPeriod">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_LongtermPollutionControlBondCurrent">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="so_CapitalInvestmentFromPrivateSources">
    <definition>Capital investment from private sources.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_InterestRateDerivativeLiabilitiesAtFairValue">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_DefinedBenefitPlanServiceCost">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsExpectedDividendRate">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="so_MinimumAnnualManagementFee">
    <definition>Minimum Annual Management Fee</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="so_ChangeInPriorServiceCostsRegulatoryAssets">
    <definition>Change in prior service costs regulatory assets.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_UnrecognizedTaxBenefitsThatWouldImpactEffectiveTaxRate">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="so_LifeOfNewIssue">
    <definition>Life of the new issue.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_AssetRetirementObligationLiabilitiesIncurred">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_OperatingLeasesFutureMinimumPaymentsDueInFiveYears">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="so_SummaryOfEstimationOfFutureBenefitPaymentsAndSubsidyReceiptsBasedOnAssumptionsUsedToMeasureAccumulatedBenefitObligationForPostretirementPlansTextBlock">
    <definition>Summary of estimation of future benefit payments and subsidy receipts based on assumptions used to measure the accumulated benefit obligation for postretirement plans text block.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_LeveragedLeasesNetInvestmentInLeveragedLeasesDisclosureRentalReceivablesNet">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_AssetRetirementObligation">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_GuaranteeObligationsCurrentCarryingValue">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="so_PaymentsForInvestmentInRestrictedCashFromRevenueBond">
    <definition>Payments For Investment In Restricted Cash From Revenue Bond.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="so_PublicUtilitiesPropertyPlantAndEquipmentOther">
    <definition>Other Equipment.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_DefinedBenefitPlanEffectOfOnePercentagePointIncreaseOnAccumulatedPostretirementBenefitObligation">
    <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="so_AmortizationOfDeferredInvestmentTaxCredits">
    <definition>Amortization of deferred investment tax credits.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_ImpairmentOrDisposalOfLongLivedAssetsPolicyTextBlock">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsExercisableNumber">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_UnrecognizedTaxBenefitsIncreasesResultingFromPriorPeriodTaxPositions">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_EmployeeServiceShareBasedCompensationTaxBenefitRealizedFromExerciseOfStockOptions">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="so_OverRecoveredFuelBalanceUnderRecoveredRegulatoryClause">
    <definition>Over Recovered Fuel Balance Under Recovered Regulatory Clause.</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_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesAvailableForGrant">
    <definition>No authoritative reference available.</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="so_CashProceedsNetOfFeesAndCommissions">
    <definition>Cash proceeds net of fees and commissions.</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_PublicUtilitiesPropertyPlantAndEquipmentTransmission">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_DefinedBenefitPlanActuarialNetGainsLosses">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="so_FairValueOfInvestmentsCalculatedAtNetAssetValue">
    <definition>Fair value of investments calculated at net asset value.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_DefinedBenefitPlanRecognizedNetGainLossDueToSettlementsAndCurtailments">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="so_ApproximateNetPositiveCashFlowResultingFromNewTaxMethod">
    <definition>Approximate net positive cash flow resulting from new tax method.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="so_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsAndMethodologyTextBlock">
    <definition>Assumptions used in the pricing model and the weighted average grant-date fair value of stock options granted.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_AssetRetirementObligationAccretionExpense">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="so_DefinedBenefitPlanExpectedFutureBenefitPaymentsAndSubsidyReceiptsTotalInYearFive">
    <definition>Defined benefit plan expected future benefit payments and subsidy receipts total in year five.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_DefinedBenefitPlanFairValueOfPlanAssets">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="so_JointlyOwnedUtilityPlantInterestsTextBlock">
    <definition>Jointly Owned Utility Plant Interests.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="so_NumberOfDaysRequireToImplementInterimCostRecoveryTariff">
    <definition>Number Of Days Require To Implement Interim Cost Recovery Tariff.</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="so_PercentageOfFinancingCostsOfConstructionWorkInProgress">
    <definition>Percentage of financing costs of construction work in progress.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="so_MaximumPowerLossOnFailureToExercisePurchaseOptionOrRenewalOptionBySubsidiaryCompany">
    <definition>Maximum Power loss on failure to exercise purchase option or renewal option by subsidiary company.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="so_OutstandingForeignCurrencyDerivativesTextBlock">
    <definition>Outstanding foreign currency derivatives.</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="so_RedemptionNoticePeriod">
    <definition>Redemption Notice Period.</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_NotionalAmountOfForeignCurrencyCashFlowHedgeDerivatives">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_DefinedBenefitPlanExpectedFutureBenefitPaymentsInYearOne">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognizedPeriodForRecognition">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_IncrementalCommonSharesAttributableToShareBasedPaymentArrangements">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_RecordedUnconditionalPurchaseObligationDueInFifthYear">
    <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_SiteStudyCostsTotal">
    <definition>Site Study Costs Total.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_AdjustmentsToAdditionalPaidInCapitalSharebasedCompensationRequisiteServicePeriodRecognitionValue">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_UnrecognizedTaxBenefitsDecreasesResultingFromPriorPeriodTaxPositions">
    <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="so_SignificantAssumptionOfTrustEarningsRateUsedToDetermineCostsForRatemaking">
    <definition>Significant assumption of trust earnings rate used to determine the costs for ratemaking.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="so_TotalSpentOnElectricGeneratingUnitConstruction">
    <definition>Total spent on electric generating unit construction.</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_ScheduleOfDerivativeInstrumentsGainLossInStatementOfFinancialPerformanceTextBlock">
    <definition>No authoritative reference available.</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="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="so_DefinedBenefitPlanReclassificationAdjustments">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="so_FairMarketValueOfFundsSecuritiesOnLoanUnderFundsManagersSecuritiesLendingProgram">
    <definition>Fair market value of fund's securities on loan under the Funds' managers' securities lending program.</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_TotalCertifiedCost">
    <definition>Total cirtified cost.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_ValuationAllowancesAndReservesDeductions">
    <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_AdjustmentsNoncashItemsToReconcileNetIncomeLossToCashProvidedByUsedInOperatingActivitiesOther">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="so_AmortizationOfRegulatoryLiabilityUpToOneThirdIfSubsidiaryDoesNotFileForRetailBaseRateIncrease">
    <definition>Amortization of regulatory liability up to one third if subsidiary does not file for retail base rate increase.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="so_ExpectedRemainingRegulatoryLiabilityToBeAmortizedInNextThreeYears">
    <definition>Expected remaining regulatory liability to be amortized in next three years.</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_AdditionalCommonStockIssuedThroughAtMarketIssuancesPursuantToSalesAgencyAgreementsRelatedToCompanysContinuousEquityOfferingProgram">
    <definition>Additional common stock issued through at the market issuances pursuant to sales agency agreements related to Southern Companys continuous equity offering program.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="so_TradingPriceRangePerCommonShareLow">
    <definition>Trading price range per common share low.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="so_SignificantAssumptionOfInflationRateUsedToDetermineCostsForRatemaking">
    <definition>Significant assumption of inflation rate used to determine the costs for ratemaking.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="so_AccruedInterestForUnrecognizedTaxBenefitsTextBlock">
    <definition>Accrued interest for unrecognized tax benefits.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="so_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionExercisableIntrinsicValue">
    <definition>Share Based Compensation Arrangement By Share Based Payment Award Option Exercisable Intrinsic Value.</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="so_EstimatedRemainingPaymentUnderLongTermServiceAgreementsForFacilitiesOwned">
    <definition>estimated remaining payment under Long-Term Service Agreements for facilities owned.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="so_NuclearDecommissioningPolicyTextBlock">
    <definition>Nuclear Decommissioning.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="so_DepreciationOfCostOfUtilityPlantInServiceCompositeStraightLineRate">
    <definition>Depreciation of cost of utility plant in service, composite straight-line rate.</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_DefinedBenefitPlanPlanAmendments">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_PublicUtilitiesPolicyTextBlock">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsExercisesInPeriodWeightedAverageExercisePrice">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsRiskFreeInterestRate">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_DerivativeAssetDesignatedAsHedgingInstrumentFairValue">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="so_MaximumProjectedRetailRoeAllowedToEarn">
    <definition>Maximum projected retail ROE allowed to earn.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="so_DamagesFromLostPropertyValuesAndRelocatingVillageCostLowerRangeLimit">
    <definition>Damages from lost property values and relocating village cost, lower range.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="so_WeightedAverageRatesAssumedInActuarialCalculationsUsedToDetermineBothBenefitObligationsAsOfMeasurementDateAndNetPeriodicCostsForPensionAndOtherPostretirementBenefitPlansTextBlock">
    <definition>Weighted average rates assumed in actuarial calculations used to determine both benefit obligations as of measurement date and net periodic costs for pension and other postretirement benefit plans text block.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="so_LongTermDebtMaturitiesRepaymentsOfPrincipalInYearThirty">
    <definition>Long Term Debt Maturities Repayments Of Principal In Year Thirty.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="so_LongTermDebtAndCapitalLeaseObligationMaturitiesRePaymentsInYearFive">
    <definition>Long Term Debt and Capital Lease Obligation Maturities Re payments In Year Five.</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_EffectiveIncomeTaxRateReconciliationNondeductibleExpenseDepreciation">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="so_MaximumAdditionalCoverageProvidedForLossesUnderExcessInsurance">
    <definition>Maximum additional coverage provided for losses under excess insurance.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_DeferredTaxAssetsGross">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="so_DefinedBenefitPlanTargetAllocationPercentageOfAssetsTotal">
    <definition>Defined Benefit Plan Target Allocation Percentage Of Assets Total.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_DefinedBenefitPlanTargetAllocationPercentageOfAssetsOther">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_ProceedsFromIssuanceOfSharesUnderIncentiveAndShareBasedCompensationPlansIncludingStockOptions">
    <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_AmountsRecognizedInConsolidatedBalanceSheetsRelatedToCompanysPensionPlansTextBlock">
    <definition>Amounts Recognized In The Consolidated Balance Sheets Related To The Companys Pension Plans.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="so_ClaimsAwardedToCompaniesRelatedToNuclearFuelDisposalLitigation">
    <definition>Claims awarded to companies related to nuclear fuel disposal litigation.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="so_UndistributedRetainedEarningsOfSubsidiaries">
    <definition>Undistributed retained earnings of the subsidiaries.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="dei_DocumentFiscalYearFocus">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="so_MaximumTaxExemptionAsPercentageOfTotalValueOfProject">
    <definition>Maximum tax exemption as a percentage of total value of project?</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="so_AmountExpensedForRatemakingPurpose">
    <definition>Amount expensed for ratemaking purpose.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="so_LongTermPurchasesCommitmentMinimumQuantityRequired">
    <definition>Sets forth the number of units of goods that must be purchased within the specified time period of the agreement to avoid penalties or unfavorable effects on pricing, among other adverse consequences.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="so_IncreaseInTariffRateOne">
    <definition>Increase In Tariff Rate One.</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="us-gaap_UnrecognizedTaxBenefitsInterestOnIncomeTaxesExpense">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="so_ConstructionAndCapitalCostsIncludedInSemiAnnualConstructionMonitoringReport">
    <definition>Construction And Capital Costs Included In Semi Annual Construction Monitoring Report</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_DefinedBenefitPlanTargetAllocationPercentageOfAssetsRealEstate">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="so_PortionIncludedInCurrentTaxLiabilitiesCurrentTaxAssetsNet">
    <definition>Portion included in current tax liabilities (current tax Assets),net.</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_AccumulatedNdrReserveReflectedAsOtherRegulatoryLiabilitiesDeferred">
    <definition>Accumulated NDR reserve reflected as other regulatory liabilities, deferred.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsExpectedVolatilityRate">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="so_EstimatedIncreaseInTariffTwo">
    <definition>Estimated Increase In Tariff Two.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="so_AccumulatedOtherComprehensiveIncomeLossbalancesNetOfTaxEffectsTextBlock">
    <definition>Accumulated other comprehensive income (loss) balances, net of tax effects.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="so_NumberOfLeveragedLeaseInvestments">
    <definition>Number of leveraged leases terminated.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="so_LongTermDebtAndCapitalLeaseObligationMaturitiesRePaymentsInNextTwelveMonths">
    <definition>Long Term Debt and Capital Lease Obligation Maturities Re payments In Next Twelve Months.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_CashAndCashEquivalentsPolicyTextBlock">
    <definition>No authoritative reference available.</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="so_BenefitsPaidNetOfDrugSubsidy">
    <definition>Benefits paid net of drug subsidy.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="so_OtherCostOfRemovalObligationsRelatedToSubsidiary">
    <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.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="so_MinimumProjectedRetailReturnOnCommonEquityAtWhichRetailRatesRemainUnchanged">
    <definition>Minimum Projected Retail Return On Common Equity At Which Retail Rates Remain Unchanged.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="so_AmountsIncludedInAccumulatedOtherComprehensiveIncomeAndRegulatoryAssetsRelatedToOtherPostretirementBenefitPlansTextBlock">
    <definition>Amounts included in accumulated other comprehensive income and regulatory assets related to the other postretirement benefit plans text block.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_EffectiveIncomeTaxRateReconciliationDeductionsQualifiedProductionActivities">
    <definition>No authoritative reference available.</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_LongTermDebtMaturitiesRepaymentsOfPrincipalInYearFour">
    <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="so_WeightedAverageFixedRatePaid">
    <definition>Weighted Average Fixed Rate Paid.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="so_LongestHedgeDate">
    <definition>Longest Hedge Date.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="so_AdditionalPortionOfInitialCompletionCostToBeAmortisedOnRenewalOfLeaseTerm">
    <definition>Additional portion of initial completion cost to be amortised on renewal of lease term.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="so_MaximumLimitOfContributionOfEmployeesBaseSalary">
    <definition>Maximum Limit Of Contribution Of Employees Base Salary.</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_TreasuryStockValue">
    <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_EarningPerShareTextBlock">
    <definition>Calculation of diluted shares used to determined diluted earnings per share.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="so_RelatedPropertyLivesInYears">
    <definition>Related property lives in years.</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_RegulatoryLiabilities">
    <definition>No authoritative reference available.</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="so_PeriodAtWhichExternalInvestmentManagersTypicallySendValuationsToBothCustodianAndToCompanyAfterQuarterEnd">
    <definition>Period At Which The External Investment Managers Typically Send Valuations To Both The Custodian And To The Company After The Quarter End.</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="so_DefinedBenefitPlanFutureAmortizationOfTransitionObligationsAssets">
    <definition>Defined Benefit Plan Future Amortization Of Transition Obligations Assets.</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_DeferredTaxLiabilitiesNoncurrent">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="so_ComponentsOfOtherPostretirementBenefitPlansNetPeriodicCostTextBlock">
    <definition>Components of other postretirement benefit plans net periodic cost text block.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="so_CostCapitalOnMine">
    <definition>Cost capital on mine.</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_SegmentReportingInformationIntersegmentRevenue">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="so_BankCreditArrangementsNoTermLoanOptionExpiresWithInOneYear">
    <definition>Bank credit arrangements no term out expires with in one year.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_SegmentReportingInformationExpendituresForAdditionsToLongLivedAssets">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="so_NotionalAmountOfInterestRateDerivativesInterestRateReceived">
    <definition>Notional Amount of Interest Rate Derivatives, Interest Rate Received.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_DefinedBenefitPlanEffectOfOnePercentagePointDecreaseOnServiceAndInterestCostComponents">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="so_NumberOfMajorInspectionCycles">
    <definition>Number of major inspection cycles per unit through which the LTSA are in effect.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="so_IncreaseInEffectOfOptions">
    <definition>Increase In Effect Of Options.</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="so_MatchingLimitOfContributionByEmployer">
    <definition>Matching limit of contribution by employer.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_AssetRetirementObligationDisclosureTextBlock">
    <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_FuelCostsPolicyTextBlock">
    <definition>Fuel Costs.</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="so_FinancialInstrumentsNotHavingCarryingAmountEqualToFairValueTextBlock">
    <definition>Financial instruments not having carrying amount equal to fair value Text Block.</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>
  <Element Id="us-gaap_DeferredTaxAssetsLiabilitiesNet">
    <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_ProceedsFromRepaymentsOfShortTermDebt">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="so_PreviouslyExpensed">
    <definition>Previously expensed.</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="so_MaximumNumberOfDaysRelatedToDollarWeightedAveragePortfolioMaturitiesRegardingCommingledFunds">
    <definition>Maximum number of days related to dollar weighted average portfolio maturities regarding commingled funds.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="so_PreTaxEffectOfUnrealizedDerivativeGainsLossesTextBlock">
    <definition>Pre Tax Effect Of Unrealized Derivative Gains Losses.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_DefinedBenefitPlanAccumulatedOtherComprehensiveIncomeNetGainsLossesBeforeTax">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="so_MaximumProjectedRetailReturnOnCommonEquityAtWhichRetailRatesRemainUnchanged">
    <definition>Maximum projected retail return on common equity at which retail rates remain unchanged.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_DefinedBenefitPlanTargetAllocationPercentageOfAssetsEquitySecurities">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="so_LifeOfNewIssueInYears">
    <definition>Life of new issue in years.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="so_AmortizedPeriodForOtherCostOfRemovalObligations">
    <definition>Amortized period for other cost of removal obligations.</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_ProceedsFromPaymentsForOtherFinancingActivities">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_InterestRateDerivativeAssetsAtFairValue">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedNumber">
    <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_ReductionInExpensesDueToSubsidyEffectOfMedicalPrescriptionDrug">
    <definition>Reduction in expenses due to subsidy effect of medical prescription Drug.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_EffectiveIncomeTaxRateReconciliationAtFederalStatutoryIncomeTaxRate">
    <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="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_InvestmentIncomeInterestAndDividend">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_FederalIncomeTaxExpenseBenefitContinuingOperations">
    <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="so_LineOfCreditExpiryYearTwo">
    <definition>Line Of Credit Expiry Year 2.</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="so_OriginalMaturitiesOfTemporaryCashInvestments">
    <definition>Original maturities of temporary cash investments.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_FairValueLiabilitiesMeasuredOnRecurringBasisDerivativeFinancialInstrumentsLiabilities">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="so_UnderRecoveredFuelBalance">
    <definition>Under recovered fuel balance.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="so_DefinedBenefitPlanFutureAmortizationOfPriorServiceCostCredit">
    <definition>Prior Service Cost, Estimated.</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_LeveragedLeasesIncomeStatementIncomeFromLeveragedLeases">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_RecordedUnconditionalPurchaseObligationDueAfterFifthYear">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_CashFlowHedgeDerivativeInstrumentAssetsAtFairValue">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="so_RefuelingCyclesMinimumMonths">
    <definition>Refueling cycles minimum months.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="so_AdditionalAccrualsOfNdrChargesReflectedAsOperationsAndMaintenanceExpense">
    <definition>Additional Accruals Of NDR Charges Reflected As Operations And Maintenance Expense.</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="us-gaap_OperatingLeasesFutureMinimumPaymentsDueInThreeYears">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_DerivativeFairValueOfDerivativeLiability">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_EnvironmentalExitCostsAssetsPreviouslyDisposedLiabilityForRemediation">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsExpectedTerm">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="so_MinimumPercentageOfCarbonDioxideThatMustCaptureAndSequesterToRemainEligibleForPhaseTwoTaxCredits">
    <definition>Minimum percentage of carbon dioxide that must capture and sequester to remain eligible for the Phase Two tax credits.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="so_ElectricGeneratingCapacityInMegaWattsUnderConsortiumAgreement">
    <definition>Electric generating capacity in Mega Watts under consortium agreement.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="so_MaximumDeductibleWaitingPeriod">
    <definition>Maximum deductible waiting period.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_EmployeeServiceShareBasedCompensationTaxBenefitFromCompensationExpense">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_ScheduleOfSegmentReportingInformationBySegmentTextBlock">
    <definition>No authoritative reference available.</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_DefinedBenefitPlanAccumulatedOtherComprehensiveIncomeNetTransitionAssetsObligationsBeforeTax">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="so_EstimatedIncreaseInBaseRevenueInYearThree">
    <definition>Estimated increase in Base Revenue in Year Three.</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="us-gaap_DebtInstrumentFaceAmount">
    <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="so_CurrentMaximumAnnualAssessments">
    <definition>Current maximum annual assessments under NEIL policies.</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="so_MinimumNumberOfMonthsRelatedToResetDateOfMaturitiesInPortfolioWithPutFeaturesOrFloatingRates">
    <definition>Minimum number of months related to the reset date of maturities in the portfolio with put features or floating rates.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_EffectiveIncomeTaxRateReconciliationPriorYearIncomeTaxes">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="so_TotalNumberOfClaimsAgainstSubsidiary">
    <definition>Total Number Of Claims Against Subsidiary.</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_DefinedBenefitPlanWeightedAverageAssetAllocations">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="so_ProceedsFromSaleOfSecuritiesHeldInExternalTrustFunds">
    <definition>Proceeds from sale of securities held in external trust funds.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_DefinedBenefitPlanUltimateHealthCareCostTrendRate">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="so_FairValueGainLoss">
    <definition>Fair Value Gain (Loss).</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_MaximumMaturityForLongerTermInvestmentGradeFixedIncomeObligations">
    <definition>Maximum maturity for longer term investment grade fixed income obligations.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_DerivativeLiabilityNotDesignatedAsHedgingInstrumentFairValue">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_DerivativeInstrumentsNotDesignatedAsHedgingInstrumentsGainLossNet">
    <definition>No authoritative reference available.</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="so_AfudcEquity">
    <definition>AFUDC Equity.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="so_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsWeightedAverageGrantDateFairValue">
    <definition>Share Based Compensation Arrangement By Share Based Payment Award Fair Value Assumptions Weighted Average Grant Date Fair Value.</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_AssetRetirementObligationsNoncurrent">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_PrescriptionDrugSubsidyReceiptsYearTwo">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="so_ImpactOnEffectiveTaxRateTextBlock">
    <definition>Impact on effective tax rate.</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="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="so_RecoveredAndAmortizedAsApprovedByAppropriateStatePSCs">
    <definition>Recovered and amortized as approved by the appropriate state PSCs .</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_PublicUtilitiesAllowanceForFundsUsedDuringConstructionCapitalizedCostOfEquity">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsForfeitedInPeriod">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="so_MaximumAggregateAmountToBePaidInOneYear">
    <definition>Maximum aggregate amount to be paid in one year.</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="so_DefinedBenefitPlanFutureAmortizationOfGainsLosses">
    <definition>Net (Gain) Loss, Estimated.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_ShorttermDebtMaximumAmountOutstandingDuringPeriod">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsExercisableWeightedAverageExercisePrice">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareAmount">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="so_LongTermDebtAndCapitalLeaseObligationMaturitiesRePaymentsInYearTwo">
    <definition>Long Term Debt and Capital Lease Obligation Maturities Re payments In Year Two.</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="so_ApproximateIncreaseInRetailRatesDueToEnvironmentalCostsForSpecifiedPeriod">
    <definition>Approximate Increase In Retail Rates Due To Environmental Costs For Specified Period.</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="so_DefinedBenefitPlanFairValueOfPlanAssetsNet">
    <definition>The fair values of pension plan assets excluding cash, receivables related to investment income, pending investments sales, and payables related to pending investment purchases, net of liabilities.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="so_DefinedBenefitPlanFairValueOfPlanAssetsWithExclusions">
    <definition>The fair values of pension plan assets excluding cash, receivables related to investment income, pending investments sales, and payables related to pending investment purchases.</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="so_UnfundedCommitments">
    <definition>Unfunded Commitments.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="so_DamagesFromLostPropertyValuesAndRelocatingVillageCostUpperRangeLimit">
    <definition>Damages from lost property values and relocating village cost, upper range.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="so_LineOfCreditExpiryYearOne">
    <definition>Line Of Credit Expiry Year 1.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_PublicUtilitiesPropertyPlantAndEquipmentPlantInService">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingIntrinsicValue">
    <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="us-gaap_OtherAssetsCurrent">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_DefinedBenefitPlanAmortizationOfTransitionObligationsAssets">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardAwardVestingPeriod">
    <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="so_IncreaseInTariffRateFour">
    <definition>Increase In Tariff Rate Four.</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="so_EstimatedCostOfDecomissioningCompletionYear">
    <definition>Estimated Cost Of Decomissioning Completion year.</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="so_AdditionalBonusDepreciationForPropertyAcquired">
    <definition>Additional bonus depreciation for property acquired.</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_DebtDisclosureTextBlock">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="so_PublicUtilitiesPropertyPlantAndEquipmentGeneral">
    <definition>Public Utilities Property Plant And Equipment General.</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="so_SignificantlyIncreaseOrDecreaseInAmountOfUnrecognizedTaxBenefits">
    <definition>Significantly Increase Or Decrease In Amount Of Unrecognized Tax Benefits.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="so_NumberOfEnvironmentalGroup">
    <definition>Number of environmental group.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_DefinedBenefitPlanGrossPrescriptionDrugSubsidyReceiptsReceived">
    <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_LeasePolicyTextBlock">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="so_ChangesInAccumulatedPostretirementBenefitObligationsAndInFairValueOfPlanAssetsTextBlock">
    <definition>Changes In The Accumulated Postretirement Benefit Obligations And In The Fair Value Of Plan Assets.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_FairValueAssetsMeasuredOnRecurringBasisCashAndCashEquivalents">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="so_LongTermDebtAndCapitalLeaseObligationMaturitiesRePaymentsInYearFour">
    <definition>Long Term Debt and Capital Lease Obligation Maturities Re payments In Year Four.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="so_PercentageOfProportionateShareOwedInConsortiumAgreement">
    <definition>Percentage of proportionate share owed in Consortium Agreement.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="so_MaximumAverageRateRseAdjustmentsForTwoYearPeriod">
    <definition>Maximum average Rate RSE adjustments for two year period.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="so_BankCreditArrangementsTermLoanOptionExpiresWithInOneYear">
    <definition>Bank credit arrangements term out expires with in one year.</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_ProceedsFromSaleOfProductiveAssets">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_EmployeeServiceShareBasedCompensationCashReceivedFromExerciseOfStockOptions">
    <definition>No authoritative reference available.</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_EstimatedCostOfDecomissioningBeginningYear">
    <definition>Estimated Cost Of Decomissioning Beginning Year.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_LeveragedLeasesBalanceSheetInvestmentInLeveragedLeases">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_DefinedBenefitPlanContributionsByEmployer">
    <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="so_UtilityPlantInService">
    <definition>Utility Plant In Service.</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_PreferredStockParOrStatedValuePerShare">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_JointlyOwnedUtilityPlantOwnershipAmountOfConstructionWorkInProgress">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="so_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsExercisableWeightedAverageRemainingContractualTerms">
    <definition>Share Based Compensation Arrangement By Share Based Payment Award Options Exercisable Weighted Average Remaining Contractual Terms.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_LeveragedLeasesNetInvestmentInLeveragedLeasesDisclosureDeferredTaxesArisingFromLeveragedLeases">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="so_ImpactOfPatientProtectionAndAffordableCareActAndHealthCareAndEducationReconciliationAct">
    <definition>Impact of the Patient Protection and Affordable Care Act and the Health Care and Education Reconciliation Act</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_OperatingLeasesFutureMinimumPaymentsDueCurrent">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_PropertyPlantAndEquipmentPolicyTextBlock">
    <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="so_DerivativesMaturityDate">
    <definition>Derivatives maturity date.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="so_BlockPeriodConsideredForInflationAdjustmentAgainstMaximumYearlyAssessment">
    <definition>Block period considered for inflation adjustment against maximum yearly assessment.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="so_BonusDepreciationForPropertyAcquired">
    <definition>Bonus depreciation for property acquired.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_PublicUtilitiesPropertyPlantAndEquipmentOtherPropertyPlantAndEquipment">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_AssetRetirementObligationLiabilitiesSettled">
    <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_PensionAndOtherPostretirementBenefitExpense">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="so_TermOfLeaseAgreement">
    <definition>Term of lease agreement by Mississippi Power Company.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="so_RegulatoryHedgeUnrealizedLoss">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_ForeignCurrencyDerivativesAtFairValueNet">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="so_DetailsOfIncomeTaxProvisionsTextBlock">
    <definition>Details of income tax provisions.</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="so_SummarizedQuarterlyFinancialDataTextBlock">
    <definition>Summarized quarterly financial data.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsExercisesInPeriodTotalIntrinsicValue">
    <definition>No authoritative reference available.</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.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_DefinedBenefitPlanExpectedFutureBenefitPaymentsInYearThree">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_FairValueMeasurementInputsDisclosureTextBlock">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_DeferredTaxAssetsValuationAllowance">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="so_GeneralPolicyTextBlock">
    <definition>General Policy.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_StateAndLocalIncomeTaxExpenseBenefitContinuingOperations">
    <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="us-gaap_IncomeTaxesPaidNet">
    <definition>No authoritative reference available.</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_AccruedReserveToCoverCostOfDamages">
    <definition>Accrued Reserve To Cover The Cost Of Storm Damages.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="so_AllowanceForFundsUsedDuringConstructionAndInterestCapitalizedPolicyTextBlock">
    <definition>Allowance for Funds Used During Construction and Interest Capitalized.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="so_AgreementsWithPlaintiffsInPendingActions">
    <definition>Agreements with plaintiffs in pending actions.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="so_GrantFundsReceivableDuringInitialOperationOfProject">
    <definition>Grant funds receivable during The Initial Operation Of Project</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="so_AssumedAverageStockPrice">
    <definition>Assumed average stock price.</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_RedeemablePreferredStockSharesOutstanding">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_DefinedBenefitPlanAccumulatedOtherComprehensiveIncomeNetPriorServiceCostCreditBeforeTax">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_DefinedBenefitPlanExpectedFutureBenefitPaymentsInFiveFiscalYearsThereafter">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="so_MaximumIncreaseInRateUnderTermsOfRateRse">
    <definition>Maximum increase in rate Under the terms of Rate RSE.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_OtherAssetsFairValueDisclosure">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_PrepaidPensionCosts">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="so_TaxPositionsNotImpactingEffectiveTaxRate">
    <definition>Tax positions not impacting effective tax rate.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_EffectiveIncomeTaxRateReconciliationOtherAdjustments">
    <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="so_MaximumPotentialCollateralRequirementsArisingFromCreditRiskRelatedContingentFeatures">
    <definition>Maximum potential collateral requirements arising the from credit-risk-related contingent features.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_OtherComprehensiveIncomeDefinedBenefitPlansNetUnamortizedGainLossArisingDuringPeriodBeforeTax">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_PublicUtilitiesPropertyPlantAndEquipmentGenerationOrProcessing">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="so_CompositionOfPensionPlanAssetsAlongWithTargetedMixOfAssetsTextBlock">
    <definition>Composition of Pension plan assets along with the targeted mix of assets.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_UnrecognizedTaxBenefitsIncreasesResultingFromCurrentPeriodTaxPositions">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_InventoryPolicyTextBlock">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsGrantsInPeriod">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_LongTermDebtPercentageBearingFixedInterestRate">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="so_DefinedBenefitPlanExpectedFutureBenefitPaymentsAndSubsidyReceiptsTotalInYearFour">
    <definition>Defined benefit plan expected future benefit payments and subsidy receipts total in year four.</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_LoansPayableToBankCurrent">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="so_AmountOfRegulatoryLiabilityAmortized">
    <definition>Amount of regulatory liability amortized.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_OperatingLeasesFutureMinimumPaymentsDueInTwoYears">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_JointlyOwnedUtilityPlantOwnershipAmountOfPlantAccumulatedDepreciation">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriod">
    <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_LineOfCreditFacilityRemainingBorrowingCapacity">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_PrescriptionDrugSubsidyReceiptsYearFive">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="so_DepreciationOfOriginalCostOfOtherPlantInServiceMaximumUsefulLiveInYears">
    <definition>Depreciation of the original cost of other plant in service, maximum useful live in years.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="so_AuthorizedLimitUnderNdrReserve">
    <definition>Authorized Limit Under NDR Reserve.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_UnrecognizedTaxBenefitsPeriodIncreaseDecrease">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="so_GainOnTerminationOfLeveragedLeaseInvestments">
    <definition>Gain on the termination of leveraged lease investments.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_ScheduleOfDefinedBenefitPlansDisclosuresTextBlock">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_AssetRetirementObligationsAndEnvironmentalCostPolicyTextBlock">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="so_RatioOfIndebtednessToCapitalizationCovenant">
    <definition>Ratio of indebtedness to capitalization covenant.</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_MaximumNumberOfMonthsRelatedToMaturitiesInPortfolioNotToExceededFromDateOfPurchase">
    <definition>Maximum number of months related to maturities in the portfolio not to exceeded from the date of purchase.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="so_LongTermDebtAndCapitalLeaseObligationMaturitiesRePaymentsInYearThree">
    <definition>Long Term Debt and Capital Lease Obligation Maturities Re payments In Year Three.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationTextBlock">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="so_InterestRatePaidOnExistingDebt">
    <definition>Interest rate paid on existing debt.</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_AllocatedShareBasedCompensationExpense">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_OperatingLeasesFutureMinimumPaymentsDueThereafter">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="so_GrantReceived">
    <definition>Grant Received</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="so_PortionOfActualEarningsAboveApprovedRoeBandRetainedBySubsidiaryCompany">
    <definition>Portion Of Actual Earnings Above Approved Roe Band Retained By Subsidiary Company.</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_DefinedBenefitPlanActualReturnOnPlanAssetsStillHeld">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_DerivativeFairValueOfDerivativeAsset">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="so_RetailReturnOnEquityRangeMinimum">
    <definition>Retail Return On Equity Range Minimum.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="so_RevenueBonds">
    <definition>Revenue Bonds.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="so_InterestReclassifiedDueToSettlements">
    <definition>Interest Reclassified Due To Settlements.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_DefinedBenefitPlanTargetAllocationPercentageOfAssetsDebtSecurities">
    <definition>No authoritative reference available.</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="us-gaap_CapitalLeaseObligationsCurrent">
    <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="so_EffectiveIncomeTaxRateReconciliationDonations">
    <definition>Effective income tax rate reconciliation donations.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_LeveragedLeasesIncomeStatementIncomeTaxExpenseOnLeveragedLeases">
    <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_PublicUtilitiesPropertyPlantAndEquipmentDistribution">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_OperatingLeasesFutureMinimumPaymentsDueInFourYears">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="so_FutureEffectiveRatesUnderRateEcrFactorInTermsOfPerUnits">
    <definition>Future Effective Rates under Rate ECR factor in terms of per units.</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="so_AdjustmentToFuelCostRecoveryRateIfUnderRecoveredFuelBalanceExceedsBudget">
    <definition>Adjustment to fuel cost recovery rate if under recovered fuel balance exceeds budget.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="so_LeveragedLeasesNetInvestmentInLeveragedLeasesDisclosureUnearnedIncome">
    <definition>Leveraged Leases Net Investment In Leveraged Leases Disclosure Unearned Income.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="so_MinimumNetWorthRequirementByOneOrMorePersonsToHoldExternalTrustFunds">
    <definition>Minimum net worth requirement by a one or more persons to hold external trust funds.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="so_MaximumRetailRoeAllowedToEarn">
    <definition>Maximum Retail ROE Allowed To Earn.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="so_MaximumCoveragePerOccurrencePerUnitLimitToObtainReplacementPower">
    <definition>Maximum coverage per occurrence per unit limit to obtain replacement power.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="so_RefuelingCyclesMaximumMonths">
    <definition>Refueling cycles maximum months.</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_LiabilitiesCurrent">
    <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="so_AmountOfVariableRatePollutionControlRevenueBondsOutstandingRequiringLiquiditySupport">
    <definition>Amount of Variable rate Pollution Control revenue Bonds Outstanding requiring Liquidity support.</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="us-gaap_OtherComprehensiveIncomeDefinedBenefitPlansNetUnamortizedGainLossArisingDuringPeriodTax">
    <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="so_MaximumPropertyDamageInsuranceProvidedToNuclearGeneratingFacilities">
    <definition>Maximum property damage insurance provided to nuclear generating facilities.</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="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_TemporaryEquityCarryingAmount">
    <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="us-gaap_DefinedBenefitPlanHealthCareCostTrendRateAssumedForNextFiscalYear">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="so_EstimatedIncreaseInTariffInYearTwo">
    <definition>Estimated increase in Environmental Compliance Cost Recovery (ECCR) Tariff.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsForfeituresAndExpirationsInPeriodWeightedAverageExercisePrice">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="so_DefinedBenefitPlanExpectedFutureBenefitPaymentsAndSubsidyReceiptsTotalInFiveFiscalYearsThereafter">
    <definition>Defined benefit plan expected future benefit payments and subsidy receipts total in five fiscal years thereafter.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_DefinedBenefitPlanExpectedFutureBenefitPaymentsInYearFour">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="so_SetPercentageOfRoeUnderArp">
    <definition>Set percentage of ROE under ARP.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="so_AmountRecordedAsReceivableOfCleanCoalPowerIntiativeRoundTwoGrantFund">
    <definition>Amount recorded as receivable of clean coal power intiative round two grant fund.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="so_ReductionInProjectedInServiceCostDueToRecoveredCost">
    <definition>Reduction in projected in-service cost due to recovery of project financing cost.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_ScheduleOfLineOfCreditFacilitiesTextBlock">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_LossContingencyClaimsSettledAndDismissedNumber">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="so_AdditionalGrantBilled">
    <definition>Additional Grant Billed</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="so_MaximumFundProvidedForPublicLiabilityClaims">
    <definition>Maximum fund provided for public liability claims arising from a single nuclear incident under Price-Anderson Amendments Act.</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="so_RedeemablePreferredStockOfSubsidiariesTextBlock">
    <definition>Redeemable Preferred Stock Of Subsidiaries.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_PrescriptionDrugSubsidyReceiptsYearOne">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_Assets">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="so_ComponentsOfOtherComprehensiveIncomeAlongWithChangesInBalancesOfRegulatoryAssetsAndRegulatoryLiabilitiesRelatedToDefinedBenefitPensionPlansTextBlock">
    <definition>Components Of Other Comprehensive Income Along With Changes In Balances Of Regulatory Assets And Regulatory Liabilities Related To Defined Benefit Pension Plans.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="so_AccumulatedDepreciationForUtilityPlantInServiceTotal">
    <definition>Accumulated depreciation for utility plant in service, total.</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="us-gaap_DefinedBenefitPlanAssumptionsUsedCalculatingNetPeriodicBenefitCostDiscountRate">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_DeferredTaxLiabilitiesRegulatoryAssetsAndLiabilities">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_JointlyOwnedUtilityPlantProportionateOwnershipShare">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_DefinedBenefitPlanExpectedReturnOnPlanAssets">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="so_ChangesInFairValueMeasurementOfLevelThreeItemsInPensionPlanAssetsTextBlock">
    <definition>Changes in the fair value measurement of the Level Three items in the pension plan assets.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="so_ChangesProjectedBenefitObligationsAndFairValueOfPlanAssetsTextBlock">
    <definition>Changes projected benefit obligations and the fair value of plan assets.</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="so_LeveragedLeasesNetInvestmentInLeveragedLeasesDisclosureCurrentTaxesPayable">
    <definition>Leveraged Leases Net Investment In Leveraged Leases Disclosure Current Taxes Payable.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="so_PreTaxEffectOfEnergyRelatedDerivativesNotDesignatedAsHedgingInstrumentsTextBlock">
    <definition>Pre Tax Effect Of Energy Related Derivatives Not Designated As Hedging Instruments</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="us-gaap_IncomeTaxDisclosureTextBlock">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="so_DepreciationOfOriginalCostOfOtherPlantInServiceMinimumUsefulLiveInYears">
    <definition>Depreciation of the original cost of other plant in service minimum useful live years.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_NetRegulatoryAssets">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="so_NetInvestmentsFromLeveragedLeaseTextBlock">
    <definition>Net Investments From Leveraged lease.</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_OtherComprehensiveIncomeReclassificationOfDefinedBenefitPlansNetGainLossRecognizedInNetPeriodicBenefitCostTax">
    <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="so_PortionOfInitialAcquisitionCostToBeAmortised">
    <definition>Portion of initial acquisition cost to be amortised (approximately).</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="so_NotionalAmountOfInterestRateDerivativesTextBlock">
    <definition>Notional amount of interest rate derivatives.</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="so_AmountOfGovernmentConstructionCostIncentivesReceived">
    <definition>Amount of government construction cost incentives received.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="so_DeductionInStatedPercentageOfQualifiedProductionActivitiesNetIncomePeriodOneAndPeriodTwo">
    <definition>Deduction In Stated Percentage Of Qualified Production Activities Net Income Period One And Period Two.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_UnrecognizedTaxBenefitsReductionsResultingFromLapseOfApplicableStatuteOfLimitations">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="so_EstimatedCostOfConstruction">
    <definition>Estimated cost of construction.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_PublicUtilitiesPropertyPlantAndEquipmentConstructionWorkInProgress">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="so_PlantCapacityUnderCoalGasificationCombinedCycleTechnology">
    <definition>Plant capacity under coal gasification combined cycle technology.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="so_CertainRegulatoryAssets">
    <definition>The net change during the reporting period in the value of certain assets that are created when regulatory agencies permits public utilities to defer costs to the balance sheet.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_DebtInstrumentCarryingAmount">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_PrescriptionDrugSubsidyReceiptsFiveFiscalYearsThereafter">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="so_RangeOfTransferPerformanceSharesToCommonStockBasedOnActualTotalShareholderReturn">
    <definition>Range of transfer performance shares to common stock based on actual Total Shareholder Return .</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="so_OperatingLeaseRenewalPeriod">
    <definition>Operating Lease renewal period.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="so_EstimatedCostOfDecomissioningTextBlock">
    <definition>Estimated Cost Of Decomissioning.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_RecordedUnconditionalPurchaseObligationDueInFourthYear">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="dei_DocumentFiscalPeriodFocus">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="so_MaximumAmountForEachLicensedReactor">
    <definition>Maximum amount that a company could be assessed per incident for each licensed reactor.</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="so_IncreaseDecreaseInAccumulatedOtherComprehensiveIncomeLossbalancesNetOfTaxEffects">
    <definition>Increase Decrease in Accumulated other comprehensive income (loss) balances, net of tax effects.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="so_RemainingLifeOfLongTermServiceAgreementsForFacilitiesOwned">
    <definition>Remaining Life of Long-Term Service Agreements for facilities owned.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="so_OtherRedeemablePreferredStockAmortization">
    <definition>The amortization of premium and capital stock expense of preferred stock that is classified as callable.</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_ShortTermBorrowings">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_LeaseAndRentalExpense">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_EffectiveIncomeTaxRateContinuingOperations">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="so_EstimatedPensionBenefitPaymentsTextBlock">
    <definition>Estimated pension benefit payments.</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_UnamortizedLossReacquiredDebtNoncurrent">
    <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_LongTermContractForPurchaseOfElectricPowerEstimatedAnnualCost">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_PropertyPlantAndEquipmentDisclosureTextBlock">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_DefinedBenefitPlanOtherPlanAssets">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_OperatingLossCarryforwards">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="so_FairValueMeasurementsOfInvestmentsCalculatedAtNetAssetValuePerShareAsWellAsNatureAndRiskOfThoseInvestmentsTextBlock">
    <definition>Fair value measurements of investments calculated at net asset value per share as well as the nature and risk of those investments.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_DerivativeAssetNotDesignatedAsHedgingInstrumentFairValue">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="so_AccumulatedProvisionsForDecommissioningTextBlock">
    <definition>Accumulated Provisions For Decommissioning.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_OperatingLeasesFutureMinimumPaymentsDue">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="so_UncollectibleAccounts">
    <definition>Average uncollectible accounts as a percentage of revenues.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_RevenueRecognitionPolicyTextBlock">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="so_ChangesInFairValueMeasurementOfLevel3ItemsTextBlock">
    <definition>Changes in the fair value measurement of the Level 3 items.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="so_EstimatedCostOfDecommissioningUsedInCurrentRates">
    <definition>Estimated Cost Of Decommissioning Used In Current Rates.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="so_AgreementReachedToAssignRemainingFunds">
    <definition>Agreement reached to assign the remaining funds</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_PrescriptionDrugSubsidyReceiptsYearFour">
    <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_DividendsCommonStockCash">
    <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_ScheduleOfDebtInstrumentsTextBlock">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_PaymentsOfStockIssuanceCosts">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="so_LossOnTerminationsOfLeveragedLeaseInvestments">
    <definition>Loss on the terminations of leveraged lease investments.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="so_PublicUtilitiesPropertyPlantAndEquipmentCommunicationsEquipment">
    <definition>Communications Equipment.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_DefinedBenefitPlanActualReturnOnPlanAssetsSoldDuringPeriod">
    <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="us-gaap_CashPaidForCapitalizedInterest">
    <definition>No authoritative reference available.</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_LeveragedLeasesBalanceSheetInvestmentInLeveragedLeasesNet">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_SummaryOfIncomeTaxContingenciesTextBlock">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="so_PercentageOfPrescriptionDrugSubsidyForMedicareEligibleRetirees">
    <definition>Percentage Of Prescription Drug Subsidy For Medicare Eligible Retirees.</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_DefinedBenefitPlanAssumptionsUsedCalculatingNetPeriodicBenefitCostRateOfCompensationIncrease">
    <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_QuarterlyFinancialInformationTextBlock">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="so_AnnualIncreaseOrDecreaseInAssumedMedicalCareCostTrendRate">
    <definition>Annual Increase Or Decrease In The Assumed Medical Care Cost Trend Rate.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_UnrecognizedTaxBenefits">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_DefinedBenefitPlanAccumulatedOtherComprehensiveIncomeBeforeTax">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="so_NumberOfStatesOutsideCompanysServiceTerritory">
    <definition>Number of states outside of Company's service territory.</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_AccumulatedDeferredInvestmentTaxCredit">
    <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_DeferredIncomeTaxExpenseBenefit">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="so_RecoveryOfProjectFinancingCostAsPerLegislation">
    <definition>Recovery of project financing cost as per Legislation.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_FairValueAssetsMeasuredOnRecurringBasisDerivativeFinancialInstrumentsAssets">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_ChangeInUnrealizedGainLossOnForeignCurrencyFairValueHedgingInstruments">
    <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_DeferredOverRecoveredRegulatoryClauseRevenues">
    <definition>Deferred Over Recovered Regulatory Clause Revenues.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_ShortTermDebtWeightedAverageInterestRate">
    <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_PensionAndOtherPostretirementDefinedBenefitPlansLiabilitiesNoncurrent">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriodWeightedAverageGrantDateFairValue">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_LineOfCreditFacilityMaximumBorrowingCapacity">
    <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_ProceedsFromIssuanceOfCommonStock">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="so_AllowanceForFundsUsedDuringConstructionAndInterestCapitalizedNetOfIncomeTaxes">
    <definition>Allowance for funds used during construction and interest capitalized, net of income taxes as a percentage of net income.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_LeveragedLeasesNetInvestmentInLeveragedLeasesDisclosureInvestmentInLeveragedLeasesNet">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="so_IncreaseInRseRate">
    <definition>Increase in RSE rate.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="so_ChangeInPriorServiceCosts">
    <definition>Change in prior service costs.</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="dei_CurrentFiscalYearEndDate">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_DefinedBenefitPlanFundedStatusOfPlan">
    <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_EmployeeServiceShareBasedCompensationUnrecognizedCompensationCostsOnNonvestedAwards">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_NotionalAmountOfInterestRateCashFlowHedgeDerivatives">
    <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_DebtInstrumentInterestRateStatedPercentageRateRangeMaximum">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_ProceedsFromIssuanceOfRedeemablePreferredStock">
    <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_OtherLongTermDebtCurrent">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="so_PurchaseOfInterest">
    <definition>Purchase Of Interest.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="so_NetQuantitySoldOfDerivativesNotDesignatedAsHedges">
    <definition>Net quantity sold of Derivatives not designated as hedges.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="so_ConstructionCostCapital">
    <definition>Construction cost capital.</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="us-gaap_PublicUtilitiesPropertyPlantAndEquipmentAmountOfAcquisitionAdjustments">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_TaxCreditCarryforwardValuationAllowance">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="so_FairValueAssetsMeasuredOnRecurringBasisTotal">
    <definition>Fair Value Assets Measured On Recurring Basis Total.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_ShorttermDebtAverageOutstandingAmount">
    <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_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetValue">
    <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_DerivativeLiabilityDesignatedAsHedgingInstrumentFairValue">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsForfeituresAndExpirationsInPeriod">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_DeferredStateAndLocalIncomeTaxExpenseBenefit">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="so_LiquiditySupportIncreasedByRemarketingsOfPollutionControlRevenueBonds">
    <definition>Liquidity support increased by Remarketings of pollution control revenue bonds.</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_RecordedUnconditionalPurchaseObligationDueInThirdYear">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_DerivativesPolicyTextBlock">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="so_FinancialDataForProductsAndServicesTextBlock">
    <definition>Financial data for products and services.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_DefinedBenefitPlanEstimatedFutureEmployerContributionsInNextFiscalYear">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_ValuationAllowancesAndReservesChargedToCostAndExpense">
    <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_DerivativeInstrumentsGainLossRecognizedInOtherComprehensiveIncomeEffectivePortionNet">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="so_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingTextBlock">
    <definition>Summary of Company's activity in the stock option plan for the current year.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="so_GrantFundsReceivableDuringConstruction">
    <definition>Grant funds receivable during construction.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_DeferredTaxLiabilities">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_DerivativeInstrumentsGainLossReclassifiedFromAccumulatedOCIIntoIncomeEffectivePortionNet">
    <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_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetGainLossIncludedInOtherComprehensiveIncome">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_OperatingLeasesOfLesseeDisclosureTextBlock">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_EnvironmentalRemediationExpense">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetGainLossIncludedInEarnings">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsGrantsInPeriodWeightedAverageExercisePrice">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="so_PeriodOverWhichCompanyHasElectedToAmortizeChangesInMarketValueOfAllPlanAssets">
    <definition>Period Over Which Company Has Elected To Amortize Changes In The Market Value Of All Plan Assets.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="so_AmountsRecognizedInConsolidatedBalanceSheetsRelatedToCompanysOtherPostretirementBenefitPlansTextBlock">
    <definition>Amounts Recognized In Consolidated Balance Sheets Related To Companys Other Postretirement benefit Plans TextBlock.</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_DefinedBenefitPlanDebtSecurities">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="so_FairValueOfCollateralReceivedAmount">
    <definition>Fair value of collateral received amount.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="so_AccumulatedDepreciationForOtherPlantInServiceTotal">
    <definition>Accumulated depreciation for other plant in service, total.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_IncreaseDecreaseInFairValueOfInterestRateFairValueHedgingInstruments">
    <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_JointlyOwnedUtilityPlantGrossOwnershipAmountOfPlantInService">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_CurrentFederalTaxExpenseBenefit">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="so_RenewalAmountOfOperatingLease">
    <definition>Maximum renewal amount of operating lease.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_DefinedBenefitPlanAssumptionsUsedCalculatingNetPeriodicBenefitCostExpectedLongTermReturnOnAssets">
    <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_TreasuryStockShares">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_RecordedUnconditionalPurchaseObligation">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="so_StockIssuedDuringPeriodSharesCompanyInvestmentPlanAndEmployeeAndDirectorStockPlans">
    <definition>Stock Issued During Period Shares Company Investment Plan And Employee And Director Stock Plans.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_DefinedBenefitPlanExpectedFutureBenefitPaymentsInYearFive">
    <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_NetIncomeLossAttributableToNoncontrollingInterest">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="so_ResidualValueGuaranteeProvisionUnderOperatingLeaseAsPercentageOfAcquisitionCost">
    <definition>Residual value guarantee provision under operating lease as percentage of the acquisition cost.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_EffectiveIncomeTaxRateReconciliationTaxCreditsInvestment">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_DeferredTaxAssetsOperatingLossCarryforwardsStateAndLocal">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="so_ProceedsFromDistributionOfRestrictedCashFromRevenueBond">
    <definition>Proceeds From Distribution Of Restricted Cash From Revenue Bond.</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="us-gaap_OtherComprehensiveIncomeUnrealizedGainLossOnDerivativesArisingDuringPeriodNetOfTax">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="so_DeductableWaitingPeriodOfSubsidiaryCompanies">
    <definition>Deductable waiting period of subsidiary companies.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_DefinedBenefitPlanAmortizationOfGainsLosses">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="so_DerivativesForwardExchangeRate">
    <definition>Derivatives forward exchange rate.</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_EffectiveIncomeTaxRateReconciliationDeductionsEmployeeStockOwnershipPlanDividends">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="so_RedemptionFrequency">
    <definition>Redemption Frequency.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_NotionalAmountOfCashFlowHedgeInstruments">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_DefinedBenefitPlanActualReturnOnPlanAssets">
    <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_OtherAssetsNoncurrent">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_SeniorNotes">
    <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_ShortTermBankLoansAndNotesPayable">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="so_UnderRecoveredFuelBalanceIncludedInDeferredChargesAndOtherAssets">
    <definition>Under Recovered Fuel Balance Included In Deferred Charges And Other Assets.</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="so_VoluntaryContributionToPensionPlan">
    <definition>Voluntary contribution to pension plan.</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_CommonStockValue">
    <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="so_TotalCapitalizationInPercent">
    <definition>Total Capitalization in Percent.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="so_AdditionalAccruedReserveToCoverCostOfDamages">
    <definition>Additional Discretionary Accrued Reserve To Cover The Cost Of Damages.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="so_DefinedBenefitPlanExpectedFutureBenefitPaymentsAndSubsidyReceiptsTotalInYearOne">
    <definition>Defined benefit plan expected future benefit payments and subsidy receipts total in year one.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_CashFlowHedgeDerivativeInstrumentLiabilitiesAtFairValue">
    <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="so_ShortTermDebtWeightedAverageInterestRates">
    <definition>Short Term Debt Weighted Average Interest Rates.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_DerivativeGainLossOnDerivativeNet">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_DefinedBenefitPlanAmortizationOfPriorServiceCostCredit">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_SharesSubjectToMandatoryRedemptionSettlementTermsMaximumAmount">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="so_TaxBenefitOnTaxCredits">
    <definition>Tax benefit on tax credits.</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="so_NetQuantityPurchaseOfDerivativesNotDesignatedAsHedges">
    <definition>Net quantity Purchase of Derivatives not designated as hedges.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="so_AverageCommitmentFees">
    <definition>Average Commitment fees.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="so_DefinedBenefitPlanExpectedFutureBenefitPaymentsAndSubsidyReceiptsTotalInYearThree">
    <definition>Defined benefit plan expected future benefit payments and subsidy receipts total in year three.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="so_MaximumInsuranceCoverage">
    <definition>Maximum insurance coverage provided by American nuclear insurers to each nuclear plant.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="so_CapitalCostToBeIncurredAtFuturePeriod">
    <definition>Capital Cost To Be Incurred at Future Period</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_ScheduleOfDerivativeInstrumentsTextBlock">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="so_ComponentsOfNetPeriodicPensionCostTextBlock">
    <definition>Components Of Net Periodic Pension Cost</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="so_PortionOfActualEarningsAboveApprovedRoeBandRefundedToCustomers">
    <definition>Portion of actual earnings above approved ROE band refunded to customers.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_UnrecognizedTaxBenefitsInterestOnIncomeTaxesAccrued">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="so_LineOfCreditExpiryCurrentYear">
    <definition>Line of credit expiry current year.</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_SharesIssued">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="so_NumberOtherElectricPowerCompaniesAgainstWhichComplaintIsFiled">
    <definition>Number other electric power companies against which complaint is filed.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="so_ReductionInTaxBasisOfAssets">
    <definition>Reduction in tax basis of assets.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_ElectricUtilityRevenue">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="so_TaxEffectsBetweenCarryingAmountsOfAssetsAndLiabilitiesTextBlock">
    <definition>Tax effects between the carrying amounts of assets and liabilities.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_RecordedUnconditionalPurchaseObligationsTextBlock">
    <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_PublicUtilitiesPropertyPlantAndEquipmentITEquipmentAndSoftware">
    <definition>IT Equipment And Software.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_DefinedBenefitPlanEffectOfOnePercentagePointIncreaseOnServiceAndInterestCostComponents">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="so_BaseRevenueUnderArp">
    <definition>Base Revenue under ARP.</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="us-gaap_DefinedBenefitPlanNetPeriodicBenefitCost">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="so_DepreciationAndAmortizationPolicyTextBlock">
    <definition>Depreciation and Amortization.</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_ProceedsFromDecommissioningFund">
    <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_DefinedBenefitPlanBenefitObligation">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="so_MaximumAssessmentExcludingApplicableStatePremiumTaxes">
    <definition>Maximum assessment, excluding any applicable state premium taxes.</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="so_ExecutableTermLoansForOneYear">
    <definition>Executable Term Loans For One Year.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_DefinedBenefitPlanAccumulatedBenefitObligation">
    <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_IncomeTaxReconciliationTaxCredits">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_RecordedUnconditionalPurchaseObligationDueInSecondYear">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="so_FairValuesOfPensionPlanAssetsTextBlock">
    <definition>The fair values of pension plan assets.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognized">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="so_TradingPriceRangePerCommonShareHigh">
    <definition>Trading price range per common share high.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="so_EstimatedIncreaseInBaseRevenueInYearTwo">
    <definition>Estimated increase in Base Revenue in Year Two.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="so_LongestNonHedgeDate">
    <definition>Longest Non-Hedge Date.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_ValuationAllowancesAndReservesBalance">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_DefinedBenefitPlanRealEstate">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_DeferredTaxAssetsRegulatoryAssetsAndLiabilities">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="so_DividendYield">
    <definition>Dividend Yield Per Share.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_LossContingencyPendingClaimsNumber">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_ValuationAllowancesAndReservesChargedToOtherAccounts">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_ComprehensiveIncomeNoteTextBlock">
    <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_MaximumAnnualRateRseAdjustmentsForTwoYearPeriod">
    <definition>Maximum Annual Rate RSE adjustments for two year period.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="so_DeductionInStatedPercentageOfQualifiedProductionActivitiesNetIncomeThereafter">
    <definition>Deduction In Stated Percentage Of Qualified Production Activities Net Income Period Six And Thereafter.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="so_RemarketingOfPuttableVariableRatePollutionControlBonds">
    <definition>Remarketing of puttable variable rate pollution control bonds.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_CommercialPaper">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="so_IncreaseDecreaseInFairValueOfSecuritiesRelatedToNuclearDecommissioning">
    <definition>Increase (Decrease) in fair value of securities related to nuclear decommissioning.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="so_RecoveryAndAmortizationPeriodsForRegulatoryAssetsLiabilitiesAverageRemainingServicePeriod">
    <definition>Recovery and amortization periods for regulatory assets (liabilities), average remaining service period.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_CurrentStateAndLocalTaxExpenseBenefit">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="so_RegulatoryAssetsAndLiabilitiesTextBlock">
    <definition>Regulatory Assets and Liabilities.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="so_RegulatoryHedgeUnrealizedGain">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_SeniorNotesCurrent">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="so_FairValueOfDerivativeLiabilitiesWithContingentFeatures">
    <definition>Fair value of derivative liabilities with contingent features.</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="so_NumberOfEmployeeParticipatingInStockOptionPlan">
    <definition>Number of employee participating in stock option plan.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="so_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionOutstandingWeightedAverageRemainingContractualTerm">
    <definition>Share Based Compensation Arrangement By Share Based Payment Award Option Outstanding Weighted Average Remaining Contractual Term.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="so_BankOneYearTermLoanAgreementPrincipalAmount">
    <definition>Bank one year term loan agreement principal amount.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="so_PerformanceOfExtensiveStudyBasedOnProjectionsOfBothAssetsAndLiabilitiesForDeterminingOptimalAssetAllocationForPensionFund">
    <definition>Performance Of Extensive Study Based On Projections Of Both Assets And Liabilities For Determining The Optimal Asset Allocation For The Pension Fund.</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="so_CivilPenaltiesUnderCleanAirActPerDayLowerRangeLimit">
    <definition>Civil penalties under clean Air Act per day, lower range.</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_DerivativeMaturityDate">
    <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="so_GainLossRelatedToLitigationSettlementAmountPerShare">
    <definition>Gain loss related to litigation settlement amount per share.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="so_AmortizationPeriodOfDeferCostsOfCertainSignificantInspectionCostsForCombustionTurbines">
    <definition>Amortization period of defer costs of certain significant inspection costs for the combustion turbines.</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="so_MaximumAggregateAmountForEachIncident">
    <definition>Maximum aggregate amount that a reactor can assess in a calender period for each incident.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="so_DefinedBenefitPlanExpectedFutureBenefitPaymentsAndSubsidyReceiptsTotalInYearTwo">
    <definition>Defined benefit plan expected future benefit payments and subsidy receipts total in year two.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="so_ExecutableTermLoansForTwoYears">
    <definition>Executable Term Loans For Two Years.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_DefinedBenefitPlanEffectOfOnePercentagePointDecreaseOnAccumulatedPostretirementBenefitObligation">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="so_StormDamageReservesPolicyTextBlock">
    <definition>Storm Damage Reserves.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_IncomeTaxPolicyTextBlock">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="so_ExpectedCollectionDueToApprovalOfTariff">
    <definition>Expected collection due to approval of tariff.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="so_NoncashPropertyAdditionsRecognized">
    <definition>Non-cash Property Additions Recognized</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="so_ComponentsOfIncomeFromLeveragedLeaseTextBlock">
    <definition>Components Of Income From Leveraged lease.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingWeightedAverageExercisePrice">
    <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_EffectiveIncomeTaxRateReconciliationStateAndLocalIncomeTaxes">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetTransfersNet">
    <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_EffectiveIncomeTaxRateReconciliationLeveragedLeaseTermination">
    <definition>Effective income tax rate reconciliation leveraged lease termination.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="so_BlockPeriodConsideredForInflationAdjustmentAgainstMaximumAssessmentPerReactor">
    <definition>Block period considered for inflation adjustment against maximum assessment per reactor.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="so_MaximumRevenueFromSingleCustomerOrIndustry">
    <definition>Number of customers or industries comprising more than 10% of total revenues.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="so_NumberOfCoalFiredGeneratingFacilitiesAtWhichNewSourceReviewViolationsOccurred">
    <definition>Number of coal fired generating facilities at which New Source Review Violations occured.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="so_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesReservedForIssuancePursuantToStockBasedCompensationPlan">
    <definition>Share based compensation arrangement by share based payment award number of shares reserved for issuance pursuant to stock based compensation plan.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_RecordedUnconditionalPurchaseObligationDueWithinOneYear">
    <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_DefinedBenefitPlanPurchasesSalesAndSettlements">
    <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="so_FrequencyOfIndemnityPayments">
    <definition>Frequency of indemnity payments.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="so_MaximumPeriodForRecoveryDeferredStormRelatedOperationsAndMaintenanceCostsAndAnyFutureReserveDeficits">
    <definition>Maximum Period for recovery deferred storm-related operations and maintenance costs and any future reserve deficits.</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="dei_EntityRegistrantName">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="so_EffectOfOnePercentAnnualIncreaseOrDecreaseInAssumedMedicalCareCostOnAPBOAndServiceAndInterestCostComponentsTextBlock">
    <definition>Effect Of One Percent Annual Increase Or Decrease In The Assumed Medical Care Cost On APBO And The Service And Interest Cost Components.</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_CashFlowHedgeLossReclassifiedToInterestExpense">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_NotionalAmountOfFairValueHedgeInstruments">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="so_PurchaseAmountOfPlantCombinedCycleGeneratingUnits">
    <definition>Purchase Amount of Plant Combined Cycle Generating Units.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="so_FairValueLiabilitiesMeasuredOnRecurringBasisLiabilitiesTotal">
    <definition>Fair Value Liabilities Measured On Recurring Basis Liabilities Total</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_EmployeeServiceShareBasedCompensationUnrecognizedCompensationCostsOnNonvestedAwardsWeightedAveragePeriodOfRecognition">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_AssetRetirementObligationRevisionOfEstimate">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_ScheduleOfDerivativeInstrumentsInStatementOfFinancialPositionFairValueTextBlock">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
</DefinitionAndReference>
