1.0.0.3 true Statement Of Cash Flows Indirect (USD $) In Millions false 1 $ false false iso4217_USD Standard http://www.xbrl.org/2003/iso4217 USD iso4217 0 iso4217_USD_per_shares Divide http://www.xbrl.org/2003/iso4217 USD iso4217 http://www.xbrl.org/2003/instance shares 0 shares Standard http://www.xbrl.org/2003/instance shares 0 false 2 $ false false iso4217_USD Standard http://www.xbrl.org/2003/iso4217 USD iso4217 0 iso4217_USD_per_shares Divide http://www.xbrl.org/2003/iso4217 USD iso4217 http://www.xbrl.org/2003/instance shares 0 shares Standard http://www.xbrl.org/2003/instance shares 0 false 3 $ false false iso4217_USD Standard http://www.xbrl.org/2003/iso4217 USD iso4217 0 iso4217_USD_per_shares Divide http://www.xbrl.org/2003/iso4217 USD iso4217 http://www.xbrl.org/2003/instance shares 0 shares Standard http://www.xbrl.org/2003/instance shares 0 2 Cash Flows From Operating Activities: 2 us-gaap true na duration string No definition available. false false false false false true false false false 1 false false 0 0 false false 2 false false 0 0 false false 3 false false 0 0 false false No definition available. false 3 Net income 2 us-gaap_ProfitLoss us-gaap true credit duration monetary No definition available. false false false false false false false false false 1 true true 394100000 394.1 false false 2 true true 395800000 395.8 false false 3 true true 416000000 416.0 false false No definition available. No authoritative reference available. false 4 Adjustments for non-cash items included in income: 2 us-gaap true na duration string No definition available. false false false false false true false false false 1 false false 0 0 false false 2 false false 0 0 false false 3 false false 0 0 false false No definition available. false 5 Depreciation and amortization 2 us-gaap_DepreciationAndAmortization us-gaap true debit duration monetary No definition available. false false false false false false false false false 1 false true 282100000 282.1 false false 2 false true 273900000 273.9 false false 3 false true 277000000 277.0 false false No definition available. No authoritative reference available. false 6 Amortization of debt related costs 2 us-gaap_AmortizationOfFinancingCosts us-gaap true debit duration monetary No definition available. false false false false false false false false false 1 false true 15400000 15.4 false false 2 false true 10900000 10.9 false false 3 false true 10100000 10.1 false false No definition available. No authoritative reference available. false 7 Amortization of power sale liability related to Ohio sale 2 aye_AmortizationOfPowerSaleLiabilityRelatedToSaleOfBusiness aye false debit duration monetary Amortization of power sale liability related to sale oOf business. false false false false false false false false false 1 false true 0 0 false false 2 false true 0 0 false false 3 false true -10500000 -10.5 false false Amortization of power sale liability related to sale oOf business. No authoritative reference available. false 8 Amortization of Pennsylvania transition assets and liabilities 2 us-gaap_AmortizationOfRegulatoryAsset us-gaap true debit duration monetary No definition available. false false false false false false false false false 1 false true -17500000 -17.5 false false 2 false true -8100000 -8.1 false false 3 false true 2200000 2.2 false false No definition available. No authoritative reference available. false 9 Gain associated with the acquisition of assets 2 aye_GainOnAcquisitionOfAssets aye false credit duration monetary Gain associated with the acquisition of assets. false false false false false false false false false 1 false true -17300000 -17.3 false false 2 false true 0 0 false false 3 false true 0 0 false false Gain associated with the acquisition of assets. No authoritative reference available. false 10 Provision for uncollectible accounts 2 us-gaap_ProvisionForDoubtfulAccounts us-gaap true debit duration monetary No definition available. false false false false false false false false false 1 false true 16400000 16.4 false false 2 false true 16500000 16.5 false false 3 false true 17300000 17.3 false false No definition available. No authoritative reference available. false 11 Deferred income taxes and investment tax credit, net 2 us-gaap_DeferredIncomeTaxesAndTaxCredits us-gaap true debit duration monetary No definition available. false false false false false false false false false 1 false true 235300000 235.3 false false 2 false true 156200000 156.2 false false 3 false true 260700000 260.7 false false No definition available. No authoritative reference available. false 12 Deferred energy costs, net 2 aye_DeferredEnergyCostsNet aye false debit duration monetary Represents the deferral of certain costs incurred to the period in which such costs are recovered in rates. false false false false false false false false false 1 false true -64400000 -64.4 false false 2 false true -63700000 -63.7 false false 3 false true -10100000 -10.1 false false Represents the deferral of certain costs incurred to the period in which such costs are recovered in rates. No authoritative reference available. false 13 Unrealized gains on derivative contracts, net 2 us-gaap_UnrealizedGainLossOnDerivatives us-gaap true credit duration monetary No definition available. false false false false false false false false false 1 false true -23400000 -23.4 false false 2 false true -18800000 -18.8 false false 3 false true -3200000 -3.2 false false No definition available. No authoritative reference available. false 14 Employee benefit expenses 2 us-gaap_PensionAndOtherPostretirementBenefitExpense us-gaap true debit duration monetary No definition available. false false false false false false false false false 1 false true 55700000 55.7 false false 2 false true 45200000 45.2 false false 3 false true 46700000 46.7 false false No definition available. No authoritative reference available. false 15 Contributions to pension and OPEB plans 2 us-gaap_PensionAndOtherPostretirementBenefitContributions us-gaap true credit duration monetary No definition available. false false false false false false false false false 1 false true -48600000 -48.6 false false 2 false true -49300000 -49.3 false false 3 false true -50000000 -50.0 false false No definition available. No authoritative reference available. false 16 Deferred revenue-Fort Martin scrubber project 2 aye_DeferredRevenueForProjects aye false debit duration monetary Represents surcharge amounts collected from West Virginia customers to pay for a portion of the costs associated with... false false false false false false false false false 1 false true 11000000 11.0 false false 2 false true 10800000 10.8 false false 3 false true 18300000 18.3 false false Represents surcharge amounts collected from West Virginia customers to pay for a portion of the costs associated with building pollution control scrubbers at Allegheny's Fort Martin power plant. These collections will be used to pay off bonds that were issued to pay for the scrubber cost. No authoritative reference available. false 17 Deferred revenue-Virginia 2 us-gaap_RecognitionOfDeferredRevenue us-gaap true credit duration monetary No definition available. false false false false false false false false false 1 false true -28300000 -28.3 false false 2 false true 28300000 28.3 false false 3 false true 0 0 false false No definition available. No authoritative reference available. false 18 Uncollected transmission revenue 2 aye_UncollectedTransmissionRevenue aye false debit duration monetary Uncollected Transmission Revenue false false false false false false false false false 1 false true -16000000 -16.0 false false 2 false true -8100000 -8.1 false false 3 false true 0 0 false false Uncollected Transmission Revenue No authoritative reference available. false 19 Accrued interest reversal-Merrill Lynch settlement 2 aye_ReversalOfAccruedInterest aye false credit duration monetary Represents the reversal of previously recorded interest expense resulting from a 3rd party settlement. false false false false false false false false false 1 false true 0 0 false false 2 false true 0 0 false false 3 false true -54700000 -54.7 false false Represents the reversal of previously recorded interest expense resulting from a 3rd party settlement. No authoritative reference available. false 20 Other, net 2 us-gaap_AdjustmentsNoncashItemsToReconcileNetIncomeLossToCashProvidedByUsedInOperatingActivitiesOther us-gaap true debit duration monetary No definition available. false false false false false false false false false 1 false true 8000000 8.0 false false 2 false true 17300000 17.3 false false 3 false true -12700000 -12.7 false false No definition available. No authoritative reference available. false 21 Changes in certain assets and liabilities: 2 us-gaap true na duration string No definition available. false false false false false true false false false 1 false false 0 0 false false 2 false false 0 0 false false 3 false false 0 0 false false No definition available. false 22 Accounts receivable, net 2 us-gaap_IncreaseDecreaseInAccountsReceivable us-gaap true credit duration monetary No definition available. false false false false false false false false false 1 false true -42900000 -42.9 false false 2 false true -26200000 -26.2 false false 3 false true -31700000 -31.7 false false No definition available. No authoritative reference available. false 23 Materials, supplies and fuel 2 us-gaap_IncreaseDecreaseInInventories us-gaap true credit duration monetary No definition available. false false false false false false false false false 1 false true -75200000 -75.2 false false 2 false true -62800000 -62.8 false false 3 false true -4500000 -4.5 false false No definition available. No authoritative reference available. false 24 Collateral deposits 2 us-gaap_IncreaseDecreaseInDepositsOutstanding us-gaap true credit duration monetary No definition available. false false false false false false false false false 1 false true 37700000 37.7 false false 2 false true 23100000 23.1 false false 3 false true -6700000 -6.7 false false No definition available. No authoritative reference available. false 25 Accounts payable 2 us-gaap_IncreaseDecreaseInAccountsPayable us-gaap true debit duration monetary No definition available. false false false false false false false false false 1 false true 29500000 29.5 false false 2 false true -36700000 -36.7 false false 3 false true 61900000 61.9 false false No definition available. No authoritative reference available. false 26 Accrued taxes 2 us-gaap_IncreaseDecreaseInAccruedIncomeTaxesPayable us-gaap true debit duration monetary No definition available. false false false false false false false false false 1 false true -29200000 -29.2 false false 2 false true 43100000 43.1 false false 3 false true -10500000 -10.5 false false No definition available. No authoritative reference available. false 27 Regulatory assets and liabilities 2 us-gaap_IncreaseDecreaseInRegulatoryAssetsAndLiabilities us-gaap true credit duration monetary No definition available. false false false false false false false false false 1 false true 32900000 32.9 false false 2 false true 111700000 111.7 false false 3 false true 17600000 17.6 false false No definition available. No authoritative reference available. false 28 Assets and liabilities related to the sale of ACC fiber 2 aye_IncreaseDecreaseInAssetsAndLiabilitiesRelatedToSaleOfACCFiber aye false credit duration monetary Increase (decrease) in assets and liabilities related to sale of ACC fiber. false false false false false false false false false 1 false true 21300000 21.3 false false 2 false true 0 0 false false 3 false true 0 0 false false Increase (decrease) in assets and liabilities related to sale of ACC fiber. No authoritative reference available. false 29 Other operating assets and liabilities 2 us-gaap_IncreaseDecreaseInOtherOperatingCapitalNet us-gaap true credit duration monetary No definition available. false false false false false false false false false 1 false true 23000000 23.0 false false 2 false true 2300000 2.3 false false 3 false true 22600000 22.6 false false No definition available. No authoritative reference available. false 30 Net cash provided by operating activities 2 us-gaap_NetCashProvidedByUsedInOperatingActivities us-gaap true na duration monetary No definition available. false false false false false false false false false 1 false true 799600000 799.6 false false 2 false true 861400000 861.4 false false 3 false true 955800000 955.8 false false No definition available. No authoritative reference available. true 31 Cash Flows From Investing Activities: 2 us-gaap true na duration string No definition available. false false false false false true false false false 1 false false 0 0 false false 2 false false 0 0 false false 3 false false 0 0 false false No definition available. false 32 Capital expenditures 2 us-gaap_PaymentsToAcquirePropertyPlantAndEquipment us-gaap true credit duration monetary No definition available. false false false false false false false false false 1 false true -1166200000 -1166.2 false false 2 false true -994100000 -994.1 false false 3 false true -848400000 -848.4 false false No definition available. No authoritative reference available. false 33 Purchase of hydroelectric business 2 us-gaap_PaymentsToAcquireBusinessesNetOfCashAcquired us-gaap true credit duration monetary No definition available. false false false false false false false false false 1 false true -2000000 -2.0 false false 2 false true 0 0 false false 3 false true 0 0 false false No definition available. No authoritative reference available. false 34 Proceeds from asset sales 2 us-gaap_ProceedsFromSaleOfProductiveAssets us-gaap true debit duration monetary No definition available. false false false false false false false false false 1 false true 3000000 3.0 false false 2 false true 1100000 1.1 false false 3 false true 1800000 1.8 false false No definition available. No authoritative reference available. false 35 Purchase of Merrill Lynch interest in subsidiary 2 us-gaap_PaymentsToAcquireAdditionalInterestInSubsidiaries us-gaap true credit duration monetary No definition available. false false false false false false false false false 1 false true 0 0 false false 2 false true -50000000 -50.0 false false 3 false true 0 0 false false No definition available. No authoritative reference available. false 36 Other investments 2 us-gaap_PaymentsToAcquireOtherInvestments us-gaap true credit duration monetary No definition available. false false false false false false false false false 1 false true -3700000 -3.7 false false 2 false true -3700000 -3.7 false false 3 false true -3300000 -3.3 false false No definition available. No authoritative reference available. false 37 Net cash used in investing activities 2 us-gaap_NetCashProvidedByUsedInInvestingActivities us-gaap true debit duration monetary No definition available. false false false false false false false false false 1 false true -1084800000 -1084.8 false false 2 false true -822300000 -822.3 false false 3 false true -1231400000 -1231.4 false false No definition available. No authoritative reference available. true 39 Cash Flows From Financing Activities: 2 us-gaap true na duration string No definition available. false false false false false true false false false 1 false false 0 0 false false 2 false false 0 0 false false 3 false false 0 0 false false No definition available. false 40 Issuance of long-term debt 2 us-gaap_ProceedsFromIssuanceOfLongTermDebt us-gaap true debit duration monetary No definition available. false false false false false false false false false 1 false true 1508300000 1508.3 false false 2 false true 647600000 647.6 false false 3 false true 936900000 936.9 false false No definition available. No authoritative reference available. false 41 Repayment of long-term debt 2 us-gaap_RepaymentsOfLongTermDebt us-gaap true credit duration monetary No definition available. false false false false false false false false false 1 false true -1177200000 -1177.2 false false 2 false true -493100000 -493.1 false false 3 false true -502200000 -502.2 false false No definition available. No authoritative reference available. false 42 Costs associated with the AE Supply revolving credit facility refinancing 2 us-gaap_PaymentsOfDebtRestructuringCosts us-gaap true credit duration monetary No definition available. false false false false false false false false false 1 false true -22200000 -22.2 false false 2 false true 0 0 false false 3 false true 0 0 false false No definition available. No authoritative reference available. false 43 Issuance (repayment) of note payable 2 us-gaap_ProceedsFromRepaymentsOfNotesPayable us-gaap true debit duration monetary No definition available. false false false false false false false false false 1 false true 0 0 false false 2 false true -10000000 -10.0 false false 3 false true 10000000 10.0 false false No definition available. No authoritative reference available. false 44 Equity contribution to PATH, LLC by a joint venture partner 2 aye_ProceedsFromContributionsFromJointVenturePartner aye false debit duration monetary The cash inflow from an entity that is a joint venture partner with the entity on a transmission expansion project. false false false false false false false false false 1 false true 8700000 8.7 false false 2 false true 4500000 4.5 false false 3 false true 0 0 false false The cash inflow from an entity that is a joint venture partner with the entity on a transmission expansion project. No authoritative reference available. false 45 Payments on capital lease obligations 2 us-gaap_RepaymentsOfLongTermCapitalLeaseObligations us-gaap true credit duration monetary No definition available. false false false false false false false false false 1 false true -8500000 -8.5 false false 2 false true -9000000 -9.0 false false 3 false true 0 0 false false No definition available. No authoritative reference available. false 46 Redemption of preferred stock of Monongahela 2 aye_PaymentsForTheRedemptionOfPreferredStockOfASubsidiary aye false credit duration monetary Payments For The Redemption Of Preferred Stock Of A Subsidiary false false false false false false false false false 1 false true 0 0 false false 2 false true 0 0 false false 3 false true -24000000 -24.0 false false Payments For The Redemption Of Preferred Stock Of A Subsidiary No authoritative reference available. false 47 Redemption premium and dividend on preferred stock of Monongahela 2 aye_RedemptionPremiumAndDividendOnPreferredStock aye false debit duration monetary Redemption Premium And Dividend On PreferredStock false false false false false false false false false 1 false true 0 0 false false 2 false true 0 0 false false 3 false true -1800000 -1.8 false false Redemption Premium And Dividend On PreferredStock No authoritative reference available. false 48 Proceeds from exercise of employee stock options 2 us-gaap_ProceedsFromStockOptionsExercised us-gaap true debit duration monetary No definition available. false false false false false false false false false 1 false true 2300000 2.3 false false 2 false true 25300000 25.3 false false 3 false true 26400000 26.4 false false No definition available. No authoritative reference available. false 49 Cash dividends paid on common stock 2 us-gaap_PaymentsOfDividendsCommonStock us-gaap true credit duration monetary No definition available. false false false false false false false false false 1 false true -101700000 -101.7 false false 2 false true -101100000 -101.1 false false 3 false true -25000000 -25.0 false false No definition available. No authoritative reference available. false 50 Net cash provided by financing activities 2 us-gaap_NetCashProvidedByUsedInFinancingActivities us-gaap true debit duration monetary No definition available. false false false false false false false false false 1 false true 209700000 209.7 false false 2 false true 64200000 64.2 false false 3 false true 420300000 420.3 false false No definition available. No authoritative reference available. true 51 Net increase (decrease) in cash and cash equivalents 2 us-gaap_CashAndCashEquivalentsPeriodIncreaseDecrease us-gaap true na duration monetary No definition available. false false false false false false false false false 1 false true -75500000 -75.5 false false 2 false true 103300000 103.3 false false 3 false true 144700000 144.7 false false No definition available. No authoritative reference available. true 52 Cash and cash equivalents at beginning of period 2 us-gaap_CashAndCashEquivalentsAtCarryingValue us-gaap true debit instant monetary No definition available. false false false false false false true false false 1 false true 362100000 362.1 false false 2 false true 258800000 258.8 false false 3 false true 114100000 114.1 false false No definition available. No authoritative reference available. false 53 Cash and cash equivalents at end of period 2 us-gaap_CashAndCashEquivalentsAtCarryingValue us-gaap true debit instant monetary No definition available. false false false false false false false true false 1 false true 286600000 286.6 false false 2 false true 362100000 362.1 false false 3 false true 258800000 258.8 false false No definition available. No authoritative reference available. false 54 Supplemental Cash Flow Information: 2 us-gaap true na duration string No definition available. false false false false false true false false false 1 false false 0 0 false false 2 false false 0 0 false false 3 false false 0 0 false false No definition available. false 55 Cash paid during the year for interest (net of amounts capitalized) 2 us-gaap_InterestPaidNet us-gaap true credit duration monetary No definition available. false false false false false false false false false 1 false true 264800000 264.8 false false 2 false true 228200000 228.2 false false 3 false true 209600000 209.6 false false No definition available. No authoritative reference available. false 56 Cash paid (received) during the year for income taxes, net 2 us-gaap_IncomeTaxesPaidNet us-gaap true credit duration monetary No definition available. false false false false false false false false false 1 false true 41300000 41.3 false false 2 false true 10800000 10.8 false false 3 false true -700000 -0.7 false false No definition available. No authoritative reference available. false 57 Accounts payable at December 31 relating to capital expenditures 2 aye_PropertyPlantAndEquipmentAdditionsInAccountsPayable aye false credit duration monetary Property, plant and equipment additions in accounts payable false false false false false false false false false 1 false true 132500000 132.5 false false 2 false true 91800000 91.8 false false 3 false true 101400000 101.4 false false Property, plant and equipment additions in accounts payable No authoritative reference available. false 58 Non-cash investing activity relating to hydroelectric business combination 2 aye_NoncashInvestingActivityRelatedToHydroelectricBusinessCombination aye false debit duration monetary Noncash Investing Activity Related To Hydroelectric Business Combination. false false false false false false false false false 1 false true 17300000 17.3 false false 2 false true 0 0 false false 3 false true 0 0 false false Noncash Investing Activity Related To Hydroelectric Business Combination. No authoritative reference available. false 59 Other 0 na true na na na No definition available. false true false false false false false false false 1 false false 0 0 false false 2 false false 0 0 false false 3 false false 0 0 false false No definition available. No authoritative reference available. false 89 Cash Flows From Investing Activities: 2 us-gaap true na duration string No definition available. false false false false false true false false false 1 false false 0 0 false false 2 false false 0 0 false false 3 false false 0 0 false false No definition available. false 96 Decrease (increase) in restricted funds 2 us-gaap_IncreaseDecreaseInRestrictedCash us-gaap true credit duration monetary No definition available. false false false false false false false false false 1 false true 300000 0.3 false false 2 false true 10700000 10.7 false false 3 false true -34500000 -34.5 false false No definition available. No authoritative reference available. false 117 Fort Martin construction 0 na true na na na No definition available. false true false false false false false false false 1 false false 0 0 false false 2 false false 0 0 false false 3 false false 0 0 false false No definition available. No authoritative reference available. false 147 Cash Flows From Investing Activities: 2 us-gaap true na duration string No definition available. false false false false false true false false false 1 false false 0 0 false false 2 false false 0 0 false false 3 false false 0 0 false false No definition available. false 154 Decrease (increase) in restricted funds 2 us-gaap_IncreaseDecreaseInRestrictedCash us-gaap true credit duration monetary No definition available. false false false false false false false false false 1 true true 83800000 83.8 false false 2 true true 213700000 213.7 false false 3 true true -347000000 -347.0 false false No definition available. No authoritative reference available. false false 3 62 false HundredThousands UnKnown UnKnown false true