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aggregate amount of payments due in the third year after the balance sheet date to reduce a recorded unconditional purchase obligation.Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Statement of Financial Accounting Standard (FAS) -Number 47 -Paragraph 10 -Subparagraph b falsefalseFuel and Purchased Power Commitments, 201313false0us-gaap_RecordedUnconditionalPurchaseObligationDueInFourthYearus-gaaptruecreditinstantNo definition available.falsefalsefalsefalsefalsefalsefalsefalsefalsefalseverboselabel1falsefalsefalse00falsefalsefalsefalsefalse2falsefalsefalse00falsefalsefalsefalsefalse3falsefalsefalse00falsefalsefalsefalsefalse4falsefalsefalse00falsefalsefalsefalsefalse5falsefalsefalse00falsefalsefalsefalsefalse6falsefalsefalse00falsefalsefalsefalsefalse7truefalsefalse208000000208000000falsefalsefalsetruefalse8falsefalsefalse00falsefalsefalsetruefalse9falsefalsefalse00falsefalsefalsetruefalse10truefalsefalse4300000043000000falsefalsefalsetruefalse11falsefalsefalse00falsefalsefalsetruefalse12falsefalsefalse00falsefalsefalsetruefalse13falsefalsefalse00falsefalsefalsetruefalse14falsefalsefalse00falsefalsefalsetruefalse15falsefalsefalse00falsefalsefalsetruefalse16falsefalsefalse00falsefalsefalsetruefalse17falsefalsefalse00falsefalsefalsetruefalse18falsefalsefalse00falsefalsefalsetruefalse19falsefalsefalse00falsefalsefalsetruefalse20falsefalsefalse00falsefalsefalsetruefalse21falsefalsefalse00falsefalsefalsetruefalseMonetaryxbrli:monetaryItemTypemonetaryThe aggregate amount of payments due in the fourth year after the balance sheet date to reduce a recorded unconditional purchase obligation.Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Statement of Financial Accounting Standard (FAS) -Number 47 -Paragraph 10 -Subparagraph b falsefalseEstimated expenditures (based on minimum contracted obligated dollars), Fourth Year14false0us-gaap_RecordedUnconditionalPurchaseObligationDueInFifthYearus-gaaptruecreditinstantNo definition available.falsefalsefalsefalsefalsefalsefalsefalsefalsefalseverboselabel1falsefalsefalse00falsefalsefalsefalsefalse2falsefalsefalse00falsefalsefalsefalsefalse3falsefalsefalse00falsefalsefalsefalsefalse4falsefalsefalse00falsefalsefalsefalsefalse5falsefalsefalse00falsefalsefalsefalsefalse6falsefalsefalse00falsefalsefalsefalsefalse7truefalsefalse141000000141000000falsefalsefalsetruefalse8falsefalsefalse00falsefalsefalsetruefalse9falsefalsefalse00falsefalsefalsetruefalse10truefalsefalse2900000029000000falsefalsefalsetruefalse11falsefalsefalse00falsefalsefalsetruefalse12falsefalsefalse00falsefalsefalsetruefalse13falsefalsefalse00falsefalsefalsetruefalse14falsefalsefalse00falsefalsefalsetruefalse15falsefalsefalse00falsefalsefalsetruefalse16falsefalsefalse00falsefalsefalsetruefalse17falsefalsefalse00falsefalsefalsetruefalse18falsefalsefalse00falsefalsefalsetruefalse19falsefalsefalse00falsefalsefalsetruefalse20falsefalsefalse00falsefalsefalsetruefalse21falsefalsefalse00falsefalsefalsetruefalseMonetaryxbrli:monetaryItemTypemonetaryThe aggregate amount of payments due in the fifth year after the balance sheet date to reduce a recorded unconditional purchase obligation.Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Statement of Financial Accounting Standard (FAS) -Number 47 -Paragraph 10 -Subparagraph b falsefalseEstimated expenditures (based on minimum contracted obligated dollars), Fifth Year15false0so_EstimatedRemainingPaymentUnderLongTermServiceAgreementsForFacilitiesOwnedsofalsedebitdurationestimated remaining payment under Long-Term Service Agreements for facilities owned.falsefalsefalsefalsefalsefalsefalsefalsefalsefalseverboselabel1falsefalsefalse00falsefalsefalsefalsefalse2falsefalsefalse00falsefalsefalsefalsefalse3falsefalsefalse00falsefalsefalsefalsefalse4truefalsefalse21000000002100000000falsefalsefalsefalsefalse5falsefalsefalse00falsefalsefalsefalsefalse6falsefalsefalse00falsefalsefalsefalsefalse7falsefalsefalse00falsefalsefalsetruefalse8falsefalsefalse00falsefalsefalsetruefalse9falsefalsefalse00falsefalsefalsetruefalse10falsefalsefalse00falsefalsefalsetruefalse11truefalsefalse60000006000000falsefalsefalsetruefalse12falsefalsefalse00falsefalsefalsetruefalse13falsefalsefalse00falsefalsefalsetruefalse14falsefalsefalse00falsefalsefalsetruefalse15falsefalsefalse00falsefalsefalsetruefalse16falsefalsefalse00falsefalsefalsetruefalse17falsefalsefalse00falsefalsefalsetruefalse18falsefalsefalse00falsefalsefalsetruefalse19falsefalsefalse00falsefalsefalsetruefalse20falsefalsefalse00falsefalsefalsetruefalse21falsefalsefalse00falsefalsefalsetruefalseMonetaryxbrli:monetaryItemTypemonetaryestimated remaining payment under Long-Term Service Agreements for facilities owned.No authoritative reference available.falsefalseTotal remaining payments to GE under the LTSA agreement16false0so_LongTermPurchasesCommitmentMinimumQuantityRequiredsofalsenadurationSets forth the number of units of goods that must be purchased within the specified time period of the agreement to avoid...falsefalsefalsefalsefalsefalsefalsefalsefalsefalseverboselabel1falsefalsefalse00falsefalsefalsefalsefalse2falsefalsefalse00falsefalsefalsefalsefalse3falsefalsefalse00falsefalsefalsefalsefalse4falsefalsefalse00falsefalsefalsefalsefalse5falsefalsefalse00falsefalsefalsefalsefalse6falsefalsefalse00falsefalsefalsefalsefalse7falsefalsefalse00falsefalsefalsetruefalse8falsefalsefalse00falsefalsefalsetruefalse9falsefalsefalse00falsefalsefalsetruefalse10truefalsefalse69000006900000falsefalsefalsetruefalse11falsefalsefalse00falsefalsefalsetruefalse12falsefalsefalse00falsefalsefalsetruefalse13falsefalsefalse00falsefalsefalsetruefalse14falsefalsefalse00falsefalsefalsetruefalse15falsefalsefalse00falsefalsefalsetruefalse16falsefalsefalse00falsefalsefalsetruefalse17falsefalsefalse00falsefalsefalsetruefalse18falsefalsefalse00falsefalsefalsetruefalse19falsefalsefalse00falsefalsefalsetruefalse20falsefalsefalse00falsefalsefalsetruefalse21falsefalsefalse00falsefalsefalsetruefalseOtherxbrli:decimalItemTypedecimalSets 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.No authoritative reference available.falsefalseMinimum contractual obligation under Limestone contracts17false0us-gaap_RecordedUnconditionalPurchaseObligationus-gaaptruecreditinstantNo definition available.falsefalsefalsefalsefalsefalsefalsefalsefalsefalseverboselabel1falsefalsefalse00falsefalsefalsefalsefalse2falsefalsefalse00falsefalsefalsefalsefalse3falsefalsefalse00falsefalsefalsefalsefalse4falsefalsefalse00falsefalsefalsefalsefalse5falsefalsefalse00falsefalsefalsefalsefalse6falsefalsefalse00falsefalsefalsefalsefalse7truefalsefalse19180000001918000000falsefalsefalsetruefalse8falsefalsefalse00falsefalsefalsetruefalse9falsefalsefalse00falsefalsefalsetruefalse10truefalsefalse282000000282000000falsefalsefalsetruefalse11falsefalsefalse00falsefalsefalsetruefalse12falsefalsefalse00falsefalsefalsetruefalse13falsefalsefalse00falsefalsefalsetruefalse14falsefalsefalse00falsefalsefalsetruefalse15falsefalsefalse00falsefalsefalsetruefalse16falsefalsefalse00falsefalsefalsetruefalse17falsefalsefalse00falsefalsefalsetruefalse18falsefalsefalse00falsefalsefalsetruefalse19falsefalsefalse00falsefalsefalsetruefalse20falsefalsefalse00falsefalsefalsetruefalse21falsefalsefalse00falsefalsefalsetruefalseMonetaryxbrli:monetaryItemTypemonetaryThe carrying amount of the long-term purchase obligation as of the balance sheet date, which equals the sum of all payments due.Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Statement of Financial Accounting Standard (FAS) -Number 47 -Paragraph 10 -Subparagraph b Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Statement of Financial Accounting Standard (FAS) -Number 47 -Paragraph 6 falsefalseMinimum contractual obligation under Limestone contracts, Amount18false0us-gaap_UtilitiesOperatingExpenseFuelUsedus-gaaptruedebitdurationNo definition available.falsefalsefalsefalsefalsefalsefalsefalsefalsefalseterselabel1falsefalsefalse00falsefalsefalsefalsefalse2falsefalsefalse00falsefalsefalsefalsefalse3falsefalsefalse00falsefalsefalsefalsefalse4truefalsefalse66990000006699000000falsefalsefalsefalsefalse5truefalsefalse59520000005952000000falsefalsefalsefalsefalse6truefalsefalse68180000006818000000falsefalsefalsefalsefalse7truefalsefalse184000000184000000falsefalsefalsetruefalse8truefalsefalse160000000160000000falsefalsefalsetruefalse9truefalsefalse147000000147000000falsefalsefalsetruefalse10falsefalsefalse00falsefalsefalsetruefalse11falsefalsefalse00falsefalsefalsetruefalse12falsefalsefalse00falsefalsefalsetruefalse13falsefalsefalse00falsefalsefalsetruefalse14falsefalsefalse00falsefalsefalsetruefalse15falsefalsefalse00falsefalsefalsetruefalse16falsefalsefalse00falsefalsefalsetruefalse17falsefalsefalse00falsefalsefalsetruefalse18falsefalsefalse00falsefalsefalsetruefalse19falsefalsefalse00falsefalsefalsetruefalse20falsefalsefalse00falsefalsefalsetruefalse21falsefalsefalse00falsefalsefalsetruefalseMonetaryxbrli:monetaryItemTypemonetaryThe amount of fuel used charged against earnings for the period.No authoritative reference available.falsefalseTotal charges for nuclear fuel included in fuel expense19false0so_MinimumAnnualManagementFeesofalsedebitdurationMinimum Annual Management Feefalsefalsefalsefalsefalsefalsefalsefalsefalsefalselabel1falsefalsefalse00falsefalsefalsefalsefalse2falsefalsefalse00falsefalsefalsefalsefalse3falsefalsefalse00falsefalsefalsefalsefalse4falsefalsefalse00falsefalsefalsefalsefalse5falsefalsefalse00falsefalsefalsefalsefalse6falsefalsefalse00falsefalsefalsefalsefalse7falsefalsefalse00falsefalsefalsetruefalse8falsefalsefalse00falsefalsefalsetruefalse9falsefalsefalse00falsefalsefalsetruefalse10falsefalsefalse00falsefalsefalsetruefalse11falsefalsefalse00falsefalsefalsetruefalse12truefalsefalse3800000038000000falsefalsefalsetruefalse13falsefalsefalse00falsefalsefalsetruefalse14falsefalsefalse00falsefalsefalsetruefalse15falsefalsefalse00falsefalsefalsetruefalse16falsefalsefalse00falsefalsefalsetruefalse17falsefalsefalse00falsefalsefalsetruefalse18falsefalsefalse00falsefalsefalsetruefalse19falsefalsefalse00falsefalsefalsetruefalse20falsefalsefalse00falsefalsefalsetruefalse21falsefalsefalse00falsefalsefalsetruefalseMonetaryxbrli:monetaryItemTypemonetaryMinimum Annual Management FeeNo authoritative reference available.falsefalseMinimum Annual Management Fee20false0so_PortionOfPartnersAssetInAssetsLeasedBySubsidiaryCompanysofalsenadurationPortion of partners asset in assets leased by the subsidiary company.falsefalsefalsefalsefalsefalsefalsefalsefalsefalseverboselabel1falsefalsefalse00falsefalsefalsefalsefalse2falsefalsefalse00falsefalsefalsefalsefalse3falsefalsefalse00falsefalsefalsefalsefalse4falsefalsefalse00falsefalsefalsefalsefalse5falsefalsefalse00falsefalsefalsefalsefalse6falsefalsefalse00falsefalsefalsefalsefalse7falsefalsefalse00falsefalsefalsetruefalse8falsefalsefalse00falsefalsefalsetruefalse9falsefalsefalse00falsefalsefalsetruefalse10falsefalsefalse00falsefalsefalsetruefalse11falsefalsefalse00falsefalsefalsetruefalse12falsefalsefalse00less than 50%less than 50%falsefalsefalsetruefalse13falsefalsefalse00falsefalsefalsetruefalse14falsefalsefalse00falsefalsefalsetruefalse15falsefalsefalse00falsefalsefalsetruefalse16falsefalsefalse00falsefalsefalsetruefalse17falsefalsefalse00falsefalsefalsetruefalse18falsefalsefalse00falsefalsefalsetruefalse19falsefalsefalse00falsefalsefalsetruefalse20falsefalsefalse00falsefalsefalsetruefalse21falsefalsefalse00falsefalsefalsetruefalseOtherxbrli:stringItemTypestringPortion of partners asset in assets leased by the subsidiary company.No authoritative reference available.falsefalsePortion of partners asset in assets leased by the subsidiary company21false0so_PurchaseAmountOfPlantCombinedCycleGeneratingUnitssofalsedebitdurationPurchase Amount of Plant Combined Cycle Generating Units.falsefalsefalsefalsefalsefalsefalsefalsefalsefalseverboselabel1falsefalsefalse00falsefalsefalsefalsefalse2falsefalsefalse00falsefalsefalsefalsefalse3falsefalsefalse00falsefalsefalsefalsefalse4falsefalsefalse00falsefalsefalsefalsefalse5falsefalsefalse00falsefalsefalsefalsefalse6falsefalsefalse00falsefalsefalsefalsefalse7falsefalsefalse00falsefalsefalsetruefalse8falsefalsefalse00falsefalsefalsetruefalse9falsefalsefalse00falsefalsefalsetruefalse10falsefalsefalse00falsefalsefalsetruefalse11falsefalsefalse00falsefalsefalsetruefalse12truefalsefalse354000000354000000falsefalsefalsetruefalse13falsefalsefalse00falsefalsefalsetruefalse14falsefalsefalse00falsefalsefalsetruefalse15falsefalsefalse00falsefalsefalsetruefalse16falsefalsefalse00falsefalsefalsetruefalse17falsefalsefalse00falsefalsefalsetruefalse18falsefalsefalse00falsefalsefalsetruefalse19falsefalsefalse00falsefalsefalsetruefalse20falsefalsefalse00falsefalsefalsetruefalse21falsefalsefalse00falsefalsefalsetruefalseMonetaryxbrli:monetaryItemTypemonetaryPurchase Amount of Plant Combined Cycle Generating Units.No authoritative reference available.falsefalsePurchase amount of Plant Daniel combined cycle generating units22false0so_RenewalAmountOfOperatingLeasesofalsedebitdurationMaximum renewal amount of operating lease.falsefalsefalsefalsefalsefalsefalsefalsefalsefalseverboselabel1falsefalsefalse00falsefalsefalsefalsefalse2falsefalsefalse00falsefalsefalsefalsefalse3falsefalsefalse00falsefalsefalsefalsefalse4falsefalsefalse00falsefalsefalsefalsefalse5falsefalsefalse00falsefalsefalsefalsefalse6falsefalsefalse00falsefalsefalsefalsefalse7falsefalsefalse00falsefalsefalsetruefalse8falsefalsefalse00falsefalsefalsetruefalse9falsefalsefalse00falsefalsefalsetruefalse10falsefalsefalse00falsefalsefalsetruefalse11falsefalsefalse00falsefalsefalsetruefalse12truefalsefalse3100000031000000falsefalsefalsetruefalse13falsefalsefalse00falsefalsefalsetruefalse14falsefalsefalse00falsefalsefalsetruefalse15falsefalsefalse00falsefalsefalsetruefalse16falsefalsefalse00falsefalsefalsetruefalse17falsefalsefalse00falsefalsefalsetruefalse18falsefalsefalse00falsefalsefalsetruefalse19falsefalsefalse00falsefalsefalsetruefalse20falsefalsefalse00falsefalsefalsetruefalse21falsefalsefalse00falsefalsefalsetruefalseMonetaryxbrli:monetaryItemTypemonetaryMaximum renewal amount of operating lease.No authoritative reference available.falsefalseRenewal amount of operating lease23false0so_TermOfLeaseAgreementsofalsenadurationTerm of lease agreement by Mississippi Power Company.falsefalsefalsefalsefalsefalsefalsefalsefalsefalseverboselabel1falsefalsefalse00falsefalsefalsefalsefalse2falsefalsefalse00falsefalsefalsefalsefalse3falsefalsefalse00falsefalsefalsefalsefalse4falsefalsefalse00falsefalsefalsefalsefalse5falsefalsefalse00falsefalsefalsefalsefalse6falsefalsefalse00falsefalsefalsefalsefalse7falsefalsefalse00falsefalsefalsetruefalse8falsefalsefalse00falsefalsefalsetruefalse9falsefalsefalse00falsefalsefalsetruefalse10falsefalsefalse00falsefalsefalsetruefalse11falsefalsefalse00falsefalsefalsetruefalse12truefalsefalse1010falsefalsefalsetruefalse13falsefalsefalse00falsefalsefalsetruefalse14falsefalsefalse00falsefalsefalsetruefalse15falsefalsefalse00falsefalsefalsetruefalse16falsefalsefalse00falsefalsefalsetruefalse17falsefalsefalse00falsefalsefalsetruefalse18falsefalsefalse00falsefalsefalsetruefalse19falsefalsefalse00falsefalsefalsetruefalse20falsefalsefalse00falsefalsefalsetruefalse21falsefalsefalse00falsefalsefalsetruefalseOtherxbrli:integerItemTypeintegerTerm of lease agreement by Mississippi Power Company.No authoritative reference available.falsefalseTerm of a lease agreement began by Mississippi Power24false0so_PortionOfInitialAcquisitionCostToBeAmortisedsofalsenadurationPortion of initial acquisition cost to be amortised (approximately).falsefalsefalsefalsefalsefalsefalsefalsefalsefalseverboselabel1falsetruefalse00falsefalsefalsefalsefalse2falsetruefalse00falsefalsefalsefalsefalse3falsetruefalse00falsefalsefalsefalsefalse4falsetruefalse00falsefalsefalsefalsefalse5falsetruefalse00falsefalsefalsefalsefalse6falsetruefalse00falsefalsefalsefalsefalse7falsetruefalse00falsefalsefalsetruefalse8falsetruefalse00falsefalsefalsetruefalse9falsetruefalse00falsefalsefalsetruefalse10falsetruefalse00falsefalsefalsetruefalse11falsetruefalse00falsefalsefalsetruefalse12truetruefalse0.040.04falsefalsefalsetruefalse13falsetruefalse00falsefalsefalsetruefalse14falsetruefalse00falsefalsefalsetruefalse15falsetruefalse00falsefalsefalsetruefalse16falsetruefalse00falsefalsefalsetruefalse17falsetruefalse00falsefalsefalsetruefalse18falsetruefalse00falsefalsefalsetruefalse19falsetruefalse00falsefalsefalsetruefalse20falsetruefalse00falsefalsefalsetruefalse21falsetruefalse00falsefalsefalsetruefalseOtherus-types:percentItemTypepurePortion of initial acquisition cost to be amortised (approximately).No authoritative reference available.falsefalsePortion of initial acquisition cost to be amortised (approximately)25false0so_OperatingLeaseRenewalPeriodsofalsenadurationOperating Lease renewal period.falsefalsefalsefalsefalsefalsefalsefalsefalsefalseverboselabel1falsefalsefalse00falsefalsefalsefalsefalse2falsefalsefalse00falsefalsefalsefalsefalse3falsefalsefalse00falsefalsefalsefalsefalse4falsefalsefalse00falsefalsefalsefalsefalse5falsefalsefalse00falsefalsefalsefalsefalse6falsefalsefalse00falsefalsefalsefalsefalse7falsefalsefalse00falsefalsefalsetruefalse8falsefalsefalse00falsefalsefalsetruefalse9falsefalsefalse00falsefalsefalsetruefalse10falsefalsefalse00falsefalsefalsetruefalse11falsefalsefalse00falsefalsefalsetruefalse12truefalsefalse1010falsefalsefalsetruefalse13falsefalsefalse00falsefalsefalsetruefalse14falsefalsefalse00falsefalsefalsetruefalse15falsefalsefalse00falsefalsefalsetruefalse16falsefalsefalse00falsefalsefalsetruefalse17falsefalsefalse00falsefalsefalsetruefalse18falsefalsefalse00falsefalsefalsetruefalse19falsefalsefalse00falsefalsefalsetruefalse20falsefalsefalse00falsefalsefalsetruefalse21falsefalsefalse00falsefalsefalsetruefalseOtherxbrli:integerItemTypeintegerOperating Lease renewal period.No authoritative reference available.falsefalseOperating Lease renewal period26false0so_AdditionalPortionOfInitialCompletionCostToBeAmortisedOnRenewalOfLeaseTermsofalsenadurationAdditional portion of initial completion cost to be amortised on renewal of lease term.falsefalsefalsefalsefalsefalsefalsefalsefalsefalseverboselabel1falsetruefalse00falsefalsefalsefalsefalse2falsetruefalse00falsefalsefalsefalsefalse3falsetruefalse00falsefalsefalsefalsefalse4falsetruefalse00falsefalsefalsefalsefalse5falsetruefalse00falsefalsefalsefalsefalse6falsetruefalse00falsefalsefalsefalsefalse7falsetruefalse00falsefalsefalsetruefalse8falsetruefalse00falsefalsefalsetruefalse9falsetruefalse00falsefalsefalsetruefalse10falsetruefalse00falsefalsefalsetruefalse11falsetruefalse00falsefalsefalsetruefalse12truetruefalse0.170.17falsefalsefalsetruefalse13falsetruefalse00falsefalsefalsetruefalse14falsetruefalse00falsefalsefalsetruefalse15falsetruefalse00falsefalsefalsetruefalse16falsetruefalse00falsefalsefalsetruefalse17falsetruefalse00falsefalsefalsetruefalse18falsetruefalse00falsefalsefalsetruefalse19falsetruefalse00falsefalsefalsetruefalse20falsetruefalse00falsefalsefalsetruefalse21falsetruefalse00falsefalsefalsetruefalseOtherus-types:percentItemTypepureAdditional portion of initial completion cost to be amortised on renewal of lease term.No authoritative reference available.falsefalseAdditional portion of initial completion cost to be amortised on renewal of lease term27false0so_MaximumPowerLossOnFailureToExercisePurchaseOptionOrRenewalOptionBySubsidiaryCompanysofalsenadurationMaximum Power loss on failure to exercise purchase option or renewal option by subsidiary company.falsefalsefalsefalsefalsefalsefalsefalsefalsefalseverboselabel1falsefalsefalse00falsefalsefalsefalsefalse2falsefalsefalse00falsefalsefalsefalsefalse3falsefalsefalse00falsefalsefalsefalsefalse4falsefalsefalse00falsefalsefalsefalsefalse5falsefalsefalse00falsefalsefalsefalsefalse6falsefalsefalse00falsefalsefalsefalsefalse7falsefalsefalse00falsefalsefalsetruefalse8falsefalsefalse00falsefalsefalsetruefalse9falsefalsefalse00falsefalsefalsetruefalse10falsefalsefalse00falsefalsefalsetruefalse11falsefalsefalse00falsefalsefalsetruefalse12falsefalsefalse0010641064falsefalsefalsetruefalse13falsefalsefalse00falsefalsefalsetruefalse14falsefalsefalse00falsefalsefalsetruefalse15falsefalsefalse00falsefalsefalsetruefalse16falsefalsefalse00falsefalsefalsetruefalse17falsefalsefalse00falsefalsefalsetruefalse18falsefalsefalse00falsefalsefalsetruefalse19falsefalsefalse00falsefalsefalsetruefalse20falsefalsefalse00falsefalsefalsetruefalse21falsefalsefalse00falsefalsefalsetruefalseOtherxbrli:stringItemTypestringMaximum Power loss on failure to exercise purchase option or renewal option by subsidiary company.No authoritative reference available.falsefalseTotal power loss if Mississippi Power doesnot exercise either its purchase option or renewal option28false0so_ResidualValueGuaranteeProvisionUnderOperatingLeaseAsPercentageOfAcquisitionCostsofalsenadurationResidual value guarantee provision under operating lease as percentage of the acquisition cost.falsefalsefalsefalsefalsefalsefalsefalsefalsefalseverboselabel1falsetruefalse00falsefalsefalsefalsefalse2falsetruefalse00falsefalsefalsefalsefalse3falsetruefalse00falsefalsefalsefalsefalse4falsetruefalse00falsefalsefalsefalsefalse5falsetruefalse00falsefalsefalsefalsefalse6falsetruefalse00falsefalsefalsefalsefalse7falsetruefalse00falsefalsefalsetruefalse8falsetruefalse00falsefalsefalsetruefalse9falsetruefalse00falsefalsefalsetruefalse10falsetruefalse00falsefalsefalsetruefalse11falsetruefalse00falsefalsefalsetruefalse12truetruefalse0.730.73falsefalsefalsetruefalse13falsetruefalse00falsefalsefalsetruefalse14falsetruefalse00falsefalsefalsetruefalse15falsetruefalse00falsefalsefalsetruefalse16falsetruefalse00falsefalsefalsetruefalse17falsetruefalse00falsefalsefalsetruefalse18falsetruefalse00falsefalsefalsetruefalse19falsetruefalse00falsefalsefalsetruefalse20falsetruefalse00falsefalsefalsetruefalse21falsetruefalse00falsefalsefalsetruefalseOtherus-types:percentItemTypepureResidual value guarantee provision under operating lease as percentage of the acquisition cost.No authoritative reference available.falsefalseResidual value guarantee provision under operating lease as percentage of the acquisition cost29false0us-gaap_GuaranteeObligationsCurrentCarryingValueus-gaaptruecreditinstantNo definition available.falsefalsefalsefalsefalsefalsefalsefalsefalsefalseverboselabel1falsefalsefalse00falsefalsefalsefalsefalse2falsefalsefalse00falsefalsefalsefalsefalse3falsefalsefalse00falsefalsefalsefalsefalse4falsefalsefalse00falsefalsefalsefalsefalse5falsefalsefalse00falsefalsefalsefalsefalse6falsefalsefalse00falsefalsefalsefalsefalse7falsefalsefalse00falsefalsefalsetruefalse8falsefalsefalse00falsefalsefalsetruefalse9falsefalsefalse00falsefalsefalsetruefalse10falsefalsefalse00falsefalsefalsetruefalse11falsefalsefalse00falsefalsefalsetruefalse12truefalsefalse20000002000000falsefalsefalsetruefalse13truefalsefalse30000003000000falsefalsefalsetruefalse14truefalsefalse50000005000000falsefalsefalsetruefalse15falsefalsefalse00falsefalsefalsetruefalse16falsefalsefalse00falsefalsefalsetruefalse17falsefalsefalse00falsefalsefalsetruefalse18falsefalsefalse00falsefalsefalsetruefalse19falsefalsefalse00falsefalsefalsetruefalse20falsefalsefalse00falsefalsefalsetruefalse21falsefalsefalse00falsefalsefalsetruefalseMonetaryxbrli:monetaryItemTypemonetaryThe current carrying amount of the liability for the freestanding or embedded guarantor's obligations under the guarantee or each group of similar guarantees.Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Statement of Financial Accounting Standard (FAS) -Number 5 -Paragraph 9 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name FASB Interpretation (FIN) -Number 45 -Paragraph 13 -Subparagraph c falsefalseLiability for fair market value of residual value guarantee30true0so_CommitmentsRelatedToLesseeTextualsAbstractsofalsenadurationCommitments related to Lessee Textuals.falsefalsefalsefalsefalsefalsefalsefalsefalsefalseverboselabel1falsefalsefalse00falsefalsefalsefalsefalse2falsefalsefalse00falsefalsefalsefalsefalse3falsefalsefalse00falsefalsefalsefalsefalse4falsefalsefalse00falsefalsefalsefalsefalse5falsefalsefalse00falsefalsefalsefalsefalse6falsefalsefalse00falsefalsefalsefalsefalse7falsefalsefalse00falsefalsefalsetruefalse8falsefalsefalse00falsefalsefalsetruefalse9falsefalsefalse00falsefalsefalsetruefalse10falsefalsefalse00falsefalsefalsetruefalse11falsefalsefalse00falsefalsefalsetruefalse12falsefalsefalse00falsefalsefalsetruefalse13falsefalsefalse00falsefalsefalsetruefalse14falsefalsefalse00falsefalsefalsetruefalse15falsefalsefalse00falsefalsefalsetruefalse16falsefalsefalse00falsefalsefalsetruefalse17falsefalsefalse00falsefalsefalsetruefalse18falsefalsefalse00falsefalsefalsetruefalse19falsefalsefalse00falsefalsefalsetruefalse20falsefalsefalse00falsefalsefalsetruefalse21falsefalsefalse00falsefalsefalsetruefalseOtherxbrli:stringItemTypestringCommitments related to Lessee Textuals.falsefalseCommitments related to Lessee [Textuals] [Abstract]31false0us-gaap_OperatingLeasesFutureMinimumPaymentsDueCurrentus-gaaptruecreditinstantNo definition available.falsefalsefalsefalsefalsefalsefalsefalsefalsefalseterselabel1falsefalsefalse00falsefalsefalsefalsefalse2falsefalsefalse00falsefalsefalsefalsefalse3falsefalsefalse00falsefalsefalsefalsefalse4truefalsefalse154000000154000000falsetruefalsefalsefalse5falsefalsefalse00falsefalsefalsefalsefalse6falsefalsefalse00falsefalsefalsefalsefalse7falsefalsefalse00falsefalsefalsetruefalse8falsefalsefalse00falsefalsefalsetruefalse9falsefalsefalse00falsefalsefalsetruefalse10falsefalsefalse00falsefalsefalsetruefalse11falsefalsefalse00falsefalsefalsetruefalse12falsefalsefalse00falsefalsefalsetruefalse13falsefalsefalse00falsefalsefalsetruefalse14falsefalsefalse00falsefalsefalsetruefalse15truefalsefalse370000000370000000falsetruefalsetruefalse16truefalsefalse4000000040000000falsetruefalsetruefalse17truefalsefalse10000001000000falsetruefalsetruefalse18truefalsefalse3900000039000000falsetruefalsetruefalse19truefalsefalse80000008000000falsetruefalsetruefalse20truefalsefalse50000005000000falsetruefalsetruefalse21truefalsefalse40000004000000falsetruefalsetruefalseMonetaryxbrli:monetaryItemTypemonetaryFor leases having an initial or remaining non-cancelable letter-terms in excess of one year, required rental payments due within one year of the balance sheet date relating to leases defined as operating.Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Statement of Financial Accounting Standard (FAS) -Number 13 -Paragraph 122 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Statement of Financial Accounting Standard (FAS) -Number 13 -Paragraph 16 -Subparagraph b(i) falsefalseLeasing cost for combined cycle generating facility2130Commitments (Details Textual) (USD $)NoRoundingUnKnownUnKnownUnKnowntruetrue