1.0.0.3 true Statement Of Shareholders Equity And Other Comprehensive Income (USD $) In Millions, except Share data false 1 $ true false false false Common stock us-gaap_StatementEquityComponentsAxis xbrldi http://xbrl.org/2006/xbrldi us-gaap_CommonStockMember us-gaap_StatementEquityComponentsAxis explicitMember iso4217_USD Standard http://www.xbrl.org/2003/iso4217 USD iso4217 0 shares Standard http://www.xbrl.org/2003/instance shares 0 false 2 $ true false false false Other paid-in capital us-gaap_StatementEquityComponentsAxis xbrldi http://xbrl.org/2006/xbrldi us-gaap_AdditionalPaidInCapitalMember us-gaap_StatementEquityComponentsAxis explicitMember iso4217_USD Standard http://www.xbrl.org/2003/iso4217 USD iso4217 0 false 3 $ true false false false Retained earnings us-gaap_StatementEquityComponentsAxis xbrldi http://xbrl.org/2006/xbrldi us-gaap_RetainedEarningsMember us-gaap_StatementEquityComponentsAxis explicitMember iso4217_USD Standard http://www.xbrl.org/2003/iso4217 USD iso4217 0 false 4 $ true false false false Treasury stock us-gaap_StatementEquityComponentsAxis xbrldi http://xbrl.org/2006/xbrldi us-gaap_TreasuryStockMember us-gaap_StatementEquityComponentsAxis explicitMember iso4217_USD Standard http://www.xbrl.org/2003/iso4217 USD iso4217 0 false 5 $ true false false false Accumulated other comprehensive loss us-gaap_StatementEquityComponentsAxis xbrldi http://xbrl.org/2006/xbrldi us-gaap_AccumulatedOtherComprehensiveIncomeMember us-gaap_StatementEquityComponentsAxis explicitMember iso4217_USD Standard http://www.xbrl.org/2003/iso4217 USD iso4217 0 false 6 $ true false false false Total Allegheny Energy, Inc. common stockholders' equity us-gaap_StatementEquityComponentsAxis xbrldi http://xbrl.org/2006/xbrldi us-gaap_ParentMember us-gaap_StatementEquityComponentsAxis explicitMember iso4217_USD Standard http://www.xbrl.org/2003/iso4217 USD iso4217 0 false 7 $ true false false false Noncontrolling interest us-gaap_StatementEquityComponentsAxis xbrldi http://xbrl.org/2006/xbrldi us-gaap_NoncontrollingInterestMember us-gaap_StatementEquityComponentsAxis explicitMember iso4217_USD Standard http://www.xbrl.org/2003/iso4217 USD iso4217 0 false 8 $ 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 6 Beginning Balance at Dec. 31, 2006 3 us-gaap_StockholdersEquityIncludingPortionAttributableToNoncontrollingInterest us-gaap true credit instant monetary No definition available. false false false true false false true false false 1 true true 206800000 206.8 true false 2 true true 1907900000 1907.9 true false 3 true true 74700000 74.7 true false 4 true true -1800000 -1.8 true false 5 true true -107200000 -107.2 true false 6 true true 2080400000 2080.4 true false 7 true true 34700000 34.7 true false 8 true true 2115100000 2115.1 false false No definition available. No authoritative reference available. false 5 Beginning Balance (in shares) at Dec. 31, 2006 3 aye_SharesOutstanding aye false na instant shares Number of shares of stock held by shareholders. false false false true false false true false false 1 false true 165360415 165360415.00 true false 2 false false 0 0 true false 3 false false 0 0 true false 4 false false 0 0 true false 5 false false 0 0 true false 6 false false 0 0 true false 7 false false 0 0 true false 8 false false 0 0 false false Number of shares of stock held by shareholders. No authoritative reference available. false 7 Net income 3 us-gaap_ProfitLoss us-gaap true credit duration monetary No definition available. false false false false false false false false false 1 false false 0 0 true false 2 false false 0 0 true false 3 false true 412200000 412.2 true false 4 false false 0 0 true false 5 false false 0 0 true false 6 false true 412200000 412.2 true false 7 false true 3800000 3.8 true false 8 false true 416000000 416.0 false false No definition available. No authoritative reference available. false 8 Defined benefit pension and other benefit plans: 3 us-gaap_OtherComprehensiveIncomeDefinedBenefitPlansAdjustmentNetOfTaxPeriodIncreaseDecreaseAbstract us-gaap true na duration string No definition available. false false false false false true false false false 1 false false 0 0 true false 2 false false 0 0 true false 3 false false 0 0 true false 4 false false 0 0 true false 5 false false 0 0 true false 6 false false 0 0 true false 7 false false 0 0 true false 8 false false 0 0 false false No definition available. false 9 Net gain (loss) during the period, net of tax of $3.1 in 2009, $(26.9) in 2008 and $10.6 in 2007 4 us-gaap_OtherComprehensiveIncomeDefinedBenefitPlansAdjustmentNetOfTaxPeriodIncreaseDecrease us-gaap true na duration monetary No definition available. false false false false false false false false false 1 false false 0 0 true false 2 false false 0 0 true false 3 false false 0 0 true false 4 false false 0 0 true false 5 false true 15700000 15.7 true false 6 false true 15700000 15.7 true false 7 false false 0 0 true false 8 false true 15700000 15.7 false false No definition available. No authoritative reference available. false 10 Amortization, net of tax of $2.1 in 2009, $1.1 in 2008 and $2.4 in 2007 4 us-gaap_OtherComprehensiveIncomeAmortizationOfDefinedBenefitPlanNetPriorServiceCostRecognizedInNetPeriodicPensionCostNetOfTax us-gaap true credit duration monetary No definition available. false false false false false false false false false 1 false false 0 0 true false 2 false false 0 0 true false 3 false false 0 0 true false 4 false false 0 0 true false 5 false true 3500000 3.5 true false 6 false true 3500000 3.5 true false 7 false false 0 0 true false 8 false true 3500000 3.5 false false No definition available. No authoritative reference available. false 11 Cash flow hedges, net of tax of $28.5 in 2009, $20.5 in 2008 and $2.9 in 2007 3 us-gaap_OtherComprehensiveIncomeDerivativesQualifyingAsHedgesNetOfTaxPeriodIncreaseDecrease us-gaap true na duration monetary No definition available. false false false false false false false false false 1 false false 0 0 true false 2 false false 0 0 true false 3 false false 0 0 true false 4 false false 0 0 true false 5 false true -4500000 -4.5 true false 6 false true -4500000 -4.5 true false 7 false false 0 0 true false 8 false true -4500000 -4.5 false false No definition available. No authoritative reference available. false 12 Effects of West Virginia Rate Order: 3 aye_EffectOfRateOrderAbstract aye false na duration string Effect Of Rate Order [Abstract] false false false false false true false false false 1 false false 0 0 true false 2 false false 0 0 true false 3 false false 0 0 true false 4 false false 0 0 true false 5 false false 0 0 true false 6 false false 0 0 true false 7 false false 0 0 true false 8 false false 0 0 false false Effect Of Rate Order [Abstract] false 13 Establishment of regulatory asset related to pension obligation, net of tax of $35.7 4 aye_EstablishmentOfRegulatoryAssetsRelatedToPensionObligationNetOfTax aye false credit duration monetary Establishment Of Regulatory Assets Related To Pension Obligation, Net Of Tax false false false false false false false false false 1 false false 0 0 true false 2 false false 0 0 true false 3 false false 0 0 true false 4 false false 0 0 true false 5 false true 52300000 52.3 true false 6 false true 52300000 52.3 true false 7 false false 0 0 true false 8 false true 52300000 52.3 false false Establishment Of Regulatory Assets Related To Pension Obligation, Net Of Tax No authoritative reference available. false 14 Adjustment related to 2005 SO2 allowance sale, net of tax of $5.8 4 aye_AdjustmentRelatedToAllowanceSO2AllowanceSaleNetOfTax aye false credit duration monetary Adjustment Related To Allowance SO2 Allowance Sale, Net Of Tax false false false false false false false false false 1 false false 0 0 true false 2 false true -8300000 -8.3 true false 3 false false 0 0 true false 4 false false 0 0 true false 5 false false 0 0 true false 6 false true -8300000 -8.3 true false 7 false false 0 0 true false 8 false true -8300000 -8.3 false false Adjustment Related To Allowance SO2 Allowance Sale, Net Of Tax No authoritative reference available. false 15 Asset swap 3 aye_EquityChangeAssetSwap2007WVRateOrder aye false debit duration monetary Represents the change in noncontrolling interests as a result of an intercompany exchange of assets within the Allegheny... false false false false false false false false false 1 false false 0 0 true false 2 false false 0 0 true false 3 false false 0 0 true false 4 false false 0 0 true false 5 false false 0 0 true false 6 false false 0 0 true false 7 false true -700000 -0.7 true false 8 false true -700000 -0.7 false false Represents the change in noncontrolling interests as a result of an intercompany exchange of assets within the Allegheny system. No authoritative reference available. false 20 Adoption of FIN 48 3 us-gaap_CumulativeEffectOfInitialAdoptionOfFIN48 us-gaap true credit duration monetary No definition available. false false false false false false false false false 1 false false 0 0 true false 2 false false 0 0 true false 3 false true -17700000 -17.7 true false 4 false false 0 0 true false 5 false false 0 0 true false 6 false true -17700000 -17.7 true false 7 false false 0 0 true false 8 false true -17700000 -17.7 false false No definition available. No authoritative reference available. false 22 Redemption of preferred stock of Monongahela 3 aye_RedemptionOfPreferredStock aye false debit duration monetary Redemption of preferred stock. false false false false false false false false false 1 false false 0 0 true false 2 false false 0 0 true false 3 false false 0 0 true false 4 false false 0 0 true false 5 false false 0 0 true false 6 false false 0 0 true false 7 false true -24000000 -24.0 true false 8 false true -24000000 -24.0 false false Redemption of preferred stock. No authoritative reference available. false 23 Adoption of measurement date provisions for pension and other benefit plans: 3 aye_AdoptionOfMeasurementDateProvisionsForPensionAndOtherBenefitPlansAbstract aye false na duration string Adoption Of Measurement Date Provisions For Pension And Other Benefit Plans [Abstract] false false false false false true false false false 1 false false 0 0 true false 2 false false 0 0 true false 3 false false 0 0 true false 4 false false 0 0 true false 5 false false 0 0 true false 6 false false 0 0 true false 7 false false 0 0 true false 8 false false 0 0 false false Adoption Of Measurement Date Provisions For Pension And Other Benefit Plans [Abstract] false 25 Premium on redemption of preferred stock of Monongahela 3 us-gaap_PreferredStockRedemptionPremium us-gaap true debit duration monetary No definition available. false false false false false false false false false 1 false false 0 0 true false 2 false true -1100000 -1.1 true false 3 false false 0 0 true false 4 false false 0 0 true false 5 false false 0 0 true false 6 false true -1100000 -1.1 true false 7 false false 0 0 true false 8 false true -1100000 -1.1 false false No definition available. No authoritative reference available. false 26 Amortizations: 3 aye_AmortizationAbstract aye false na duration string Amortization [Abstract] false false false false false true false false false 1 false false 0 0 true false 2 false false 0 0 true false 3 false false 0 0 true false 4 false false 0 0 true false 5 false false 0 0 true false 6 false false 0 0 true false 7 false false 0 0 true false 8 false false 0 0 false false Amortization [Abstract] false 30 Dividends on preferred stock of Monongahela 3 us-gaap_DividendsPreferredStock us-gaap true debit duration monetary No definition available. false false false false false false false false false 1 false false 0 0 true false 2 false false 0 0 true false 3 false false 0 0 true false 4 false false 0 0 true false 5 false false 0 0 true false 6 false false 0 0 true false 7 false true -700000 -0.7 true false 8 false true -700000 -0.7 false false No definition available. No authoritative reference available. false 31 Dividends on common stock 3 us-gaap_DividendsCommonStock us-gaap true debit duration monetary No definition available. false false false false false false false false false 1 false false 0 0 true false 2 false false 0 0 true false 3 false true -25000000 -25.0 true false 4 false false 0 0 true false 5 false false 0 0 true false 6 false true -25000000 -25.0 true false 7 false false 0 0 true false 8 false true -25000000 -25.0 false false No definition available. No authoritative reference available. false 32 Stock-based compensation expense: 3 us-gaap_ShareBasedCompensationAbstract us-gaap true na duration string No definition available. false false false false false true false false false 1 false false 0 0 true false 2 false false 0 0 true false 3 false false 0 0 true false 4 false false 0 0 true false 5 false false 0 0 true false 6 false false 0 0 true false 7 false false 0 0 true false 8 false false 0 0 false false No definition available. false 33 Stock units 4 us-gaap_StockIssuedDuringPeriodValueNewIssues us-gaap true credit duration monetary No definition available. false false false false false false false false false 1 false false 0 0 true false 2 false true 2400000 2.4 true false 3 false false 0 0 true false 4 false false 0 0 true false 5 false false 0 0 true false 6 false true 2400000 2.4 true false 7 false false 0 0 true false 8 false true 2400000 2.4 false false No definition available. No authoritative reference available. false 34 Non-employee director stock awards (in shares) 4 aye_StockIssuedDuringPeriodSharesDirectorStockAward aye false na duration shares Represents the number of shares issued during the period for non-employee director stock awards. false false false false false false false false false 1 false true 18300 18300.00 true false 2 false false 0 0 true false 3 false false 0 0 true false 4 false false 0 0 true false 5 false false 0 0 true false 6 false false 0 0 true false 7 false false 0 0 true false 8 false false 0 0 false false Represents the number of shares issued during the period for non-employee director stock awards. No authoritative reference available. false 35 Non-employee director stock awards 4 aye_StockIssuedDuringPeriodValueDirectorStockAward aye false credit duration monetary Par value stock issued during the period as a result of the issuance of non-employee director stock awards. false false false false false false false false false 1 false false 0 0 true false 2 false true 900000 0.9 true false 3 false false 0 0 true false 4 false false 0 0 true false 5 false false 0 0 true false 6 false true 900000 0.9 true false 7 false false 0 0 true false 8 false true 900000 0.9 false false Par value stock issued during the period as a result of the issuance of non-employee director stock awards. No authoritative reference available. false 36 Stock options 4 us-gaap_AdjustmentsToAdditionalPaidInCapitalSharebasedCompensationRequisiteServicePeriodRecognitionValue us-gaap true credit duration monetary No definition available. false false false false false false false false false 1 false false 0 0 true false 2 false true 7000000 7.0 true false 3 false false 0 0 true false 4 false false 0 0 true false 5 false false 0 0 true false 6 false true 7000000 7.0 true false 7 false false 0 0 true false 8 false true 7000000 7.0 false false No definition available. No authoritative reference available. false 40 Exercise of stock options (in shares) 3 us-gaap_StockIssuedDuringPeriodSharesStockOptionsExercised us-gaap true na duration shares No definition available. false false false false false false false false false 1 false true 1445969 1445969.00 true false 2 false false 0 0 true false 3 false false 0 0 true false 4 false false 0 0 true false 5 false false 0 0 true false 6 false false 0 0 true false 7 false false 0 0 true false 8 false false 0 0 false false No definition available. No authoritative reference available. false 41 Exercise of stock options 3 us-gaap_StockIssuedDuringPeriodValueStockOptionsExercised us-gaap true credit duration monetary No definition available. false false false false false false false false false 1 false true 1800000 1.8 true false 2 false true 24600000 24.6 true false 3 false false 0 0 true false 4 false false 0 0 true false 5 false false 0 0 true false 6 false true 26400000 26.4 true false 7 false false 0 0 true false 8 false true 26400000 26.4 false false No definition available. No authoritative reference available. false 42 Settlement of stock units (in shares) 3 aye_StockIssuedDuringPeriodSharesStockUnits aye false na duration shares Number of stock units issued. false false false false false false false false false 1 false true 373395 373395.00 true false 2 false false 0 0 true false 3 false false 0 0 true false 4 false false 0 0 true false 5 false false 0 0 true false 6 false false 0 0 true false 7 false false 0 0 true false 8 false false 0 0 false false Number of stock units issued. No authoritative reference available. false 43 Settlement of stock units 3 aye_StockIssuedDuringPeriodStockUnits aye false credit duration monetary Value stock issued during the period as a result of the settlement of stock units. false false false false false false false false false 1 false true 500000 0.5 true false 2 false true -9300000 -9.3 true false 3 false false 0 0 true false 4 false false 0 0 true false 5 false false 0 0 true false 6 false true -8800000 -8.8 true false 7 false false 0 0 true false 8 false true -8800000 -8.8 false false Value stock issued during the period as a result of the settlement of stock units. No authoritative reference available. false 46 Settlement of performance shares 3 aye_SettlementOfPerformanceShares aye false na duration shares Settlement of performance shares. false false false false false false false false false 1 false true 25497 25497.00 true false 2 false false 0 0 true false 3 false false 0 0 true false 4 false false 0 0 true false 5 false false 0 0 true false 6 false false 0 0 true false 7 false false 0 0 true false 8 false false 0 0 false false Settlement of performance shares. No authoritative reference available. false 47 Other 3 us-gaap_StockholdersEquityOther us-gaap true debit duration monetary No definition available. false false false false false false false false false 1 false false 0 0 true false 2 false false 0 0 true false 3 false false 0 0 true false 4 false false 0 0 true false 5 false false 0 0 true false 6 false false 0 0 true false 7 false true 100000 0.1 true false 8 false true 100000 0.1 false false No definition available. No authoritative reference available. false 48 Ending Balance (in shares) at Dec. 31, 2007 3 aye_SharesOutstanding aye false na instant shares Number of shares of stock held by shareholders. false false false true false false false true false 1 false true 167223576 167223576.00 true false 2 false false 0 0 true false 3 false false 0 0 true false 4 false false 0 0 true false 5 false false 0 0 true false 6 false false 0 0 true false 7 false false 0 0 true false 8 false false 0 0 false false Number of shares of stock held by shareholders. No authoritative reference available. false 49 Ending Balance at Dec. 31, 2007 3 us-gaap_StockholdersEquityIncludingPortionAttributableToNoncontrollingInterest us-gaap true credit instant monetary No definition available. false false false true false false false true false 1 false true 209100000 209.1 true false 2 false true 1924100000 1924.1 true false 3 false true 444200000 444.2 true false 4 false true -1800000 -1.8 true false 5 false true -40200000 -40.2 true false 6 false true 2535400000 2535.4 true false 7 false true 13200000 13.2 true false 8 false true 2548600000 2548.6 false false No definition available. No authoritative reference available. false 7 Net income 3 us-gaap_ProfitLoss us-gaap true credit duration monetary No definition available. false false false false false false false false false 1 false false 0 0 true false 2 false false 0 0 true false 3 false true 395400000 395.4 true false 4 false false 0 0 true false 5 false false 0 0 true false 6 false true 395400000 395.4 true false 7 false true 400000 0.4 true false 8 false true 395800000 395.8 false false No definition available. No authoritative reference available. false 8 Defined benefit pension and other benefit plans: 3 us-gaap_OtherComprehensiveIncomeDefinedBenefitPlansAdjustmentNetOfTaxPeriodIncreaseDecreaseAbstract us-gaap true na duration string No definition available. false false false false false true false false false 1 false false 0 0 true false 2 false false 0 0 true false 3 false false 0 0 true false 4 false false 0 0 true false 5 false false 0 0 true false 6 false false 0 0 true false 7 false false 0 0 true false 8 false false 0 0 false false No definition available. false 9 Net gain (loss) during the period, net of tax of $3.1 in 2009, $(26.9) in 2008 and $10.6 in 2007 4 us-gaap_OtherComprehensiveIncomeDefinedBenefitPlansAdjustmentNetOfTaxPeriodIncreaseDecrease us-gaap true na duration monetary No definition available. false false false false false false false false false 1 false false 0 0 true false 2 false false 0 0 true false 3 false false 0 0 true false 4 false false 0 0 true false 5 false true -39500000 -39.5 true false 6 false true -39500000 -39.5 true false 7 false false 0 0 true false 8 false true -39500000 -39.5 false false No definition available. No authoritative reference available. false 10 Amortization, net of tax of $2.1 in 2009, $1.1 in 2008 and $2.4 in 2007 4 us-gaap_OtherComprehensiveIncomeAmortizationOfDefinedBenefitPlanNetPriorServiceCostRecognizedInNetPeriodicPensionCostNetOfTax us-gaap true credit duration monetary No definition available. false false false false false false false false false 1 false false 0 0 true false 2 false false 0 0 true false 3 false false 0 0 true false 4 false false 0 0 true false 5 false true 1700000 1.7 true false 6 false true 1700000 1.7 true false 7 false false 0 0 true false 8 false true 1700000 1.7 false false No definition available. No authoritative reference available. false 11 Cash flow hedges, net of tax of $28.5 in 2009, $20.5 in 2008 and $2.9 in 2007 3 us-gaap_OtherComprehensiveIncomeDerivativesQualifyingAsHedgesNetOfTaxPeriodIncreaseDecrease us-gaap true na duration monetary No definition available. false false false false false false false false false 1 false false 0 0 true false 2 false false 0 0 true false 3 false false 0 0 true false 4 false false 0 0 true false 5 false true 32400000 32.4 true false 6 false true 32400000 32.4 true false 7 false false 0 0 true false 8 false true 32400000 32.4 false false No definition available. No authoritative reference available. false 12 Effects of West Virginia Rate Order: 3 aye_EffectOfRateOrderAbstract aye false na duration string Effect Of Rate Order [Abstract] false false false false false true false false false 1 false false 0 0 true false 2 false false 0 0 true false 3 false false 0 0 true false 4 false false 0 0 true false 5 false false 0 0 true false 6 false false 0 0 true false 7 false false 0 0 true false 8 false false 0 0 false false Effect Of Rate Order [Abstract] false 19 Purchase of noncontrolling interest in AE Supply 3 us-gaap_MinorityInterestDecreaseFromRedemptions us-gaap true debit duration monetary No definition available. false false false false false false false false false 1 false false 0 0 true false 2 false false 0 0 true false 3 false false 0 0 true false 4 false false 0 0 true false 5 false false 0 0 true false 6 false false 0 0 true false 7 false true -13200000 -13.2 true false 8 false true -13200000 -13.2 false false No definition available. No authoritative reference available. false 21 Equity contribution to PATH, LLC by the joint venture partner 3 aye_ContributionsFromNoncontrollingInterests aye false credit duration monetary Contributions from noncontrolling interests. false false false false false false false false false 1 false false 0 0 true false 2 false false 0 0 true false 3 false false 0 0 true false 4 false false 0 0 true false 5 false false 0 0 true false 6 false false 0 0 true false 7 false true 4500000 4.5 true false 8 false true 4500000 4.5 false false Contributions from noncontrolling interests. No authoritative reference available. false 23 Adoption of measurement date provisions for pension and other benefit plans: 3 aye_AdoptionOfMeasurementDateProvisionsForPensionAndOtherBenefitPlansAbstract aye false na duration string Adoption Of Measurement Date Provisions For Pension And Other Benefit Plans [Abstract] false false false false false true false false false 1 false false 0 0 true false 2 false false 0 0 true false 3 false false 0 0 true false 4 false false 0 0 true false 5 false false 0 0 true false 6 false false 0 0 true false 7 false false 0 0 true false 8 false false 0 0 false false Adoption Of Measurement Date Provisions For Pension And Other Benefit Plans [Abstract] false 24 Service cost, interest cost and expected return on plan assets, net of tax of $3.0 4 aye_ServiceCostInterestCostAndExpectedReturnOnPlanAssetsNetOfTax aye false credit duration monetary Service Cost, Interest Cost And Expected Return On Plan Assets, Net Of Tax false false false false false false false false false 1 false false 0 0 true false 2 false false 0 0 true false 3 false true -4400000 -4.4 true false 4 false false 0 0 true false 5 false false 0 0 true false 6 false true -4400000 -4.4 true false 7 false false 0 0 true false 8 false true -4400000 -4.4 false false Service Cost, Interest Cost And Expected Return On Plan Assets, Net Of Tax No authoritative reference available. false 26 Amortizations: 3 aye_AmortizationAbstract aye false na duration string Amortization [Abstract] false false false false false true false false false 1 false false 0 0 true false 2 false false 0 0 true false 3 false false 0 0 true false 4 false false 0 0 true false 5 false false 0 0 true false 6 false false 0 0 true false 7 false false 0 0 true false 8 false false 0 0 false false Amortization [Abstract] false 27 Net actuarial loss, net of tax of $0.7 4 aye_AmortizationNetActuarialLossNetOfTax aye false credit duration monetary Amortization Net Actuarial Loss, Net Of Tax false false false false false false false false false 1 false false 0 0 true false 2 false false 0 0 true false 3 false true -1000000 -1.0 true false 4 false false 0 0 true false 5 false true 1000000 1.0 true false 6 false false 0 0 true false 7 false false 0 0 true false 8 false true 0 0 false false Amortization Net Actuarial Loss, Net Of Tax No authoritative reference available. false 28 Net transition obligation, net of tax of $0.6 4 aye_AmortizationNetTransitionObligationNetOfTax aye false credit duration monetary Amortization Net Transition Obligation, Net Of Tax false false false false false false false false false 1 false false 0 0 true false 2 false false 0 0 true false 3 false true -900000 -0.9 true false 4 false false 0 0 true false 5 false true 900000 0.9 true false 6 false false 0 0 true false 7 false false 0 0 true false 8 false true 0 0 false false Amortization Net Transition Obligation, Net Of Tax No authoritative reference available. false 29 Net prior service cost, net of tax of $0.3 4 aye_AmortizationNetPriorServiceCostsNetOfTax aye false credit duration monetary Amortization Net Prior Service Costs, Net Of Tax false false false false false false false false false 1 false false 0 0 true false 2 false false 0 0 true false 3 false true -500000 -0.5 true false 4 false false 0 0 true false 5 false true 500000 0.5 true false 6 false false 0 0 true false 7 false false 0 0 true false 8 false true 0 0 false false Amortization Net Prior Service Costs, Net Of Tax No authoritative reference available. false 31 Dividends on common stock 3 us-gaap_DividendsCommonStock us-gaap true debit duration monetary No definition available. false false false false false false false false false 1 false false 0 0 true false 2 false false 0 0 true false 3 false true -101100000 -101.1 true false 4 false false 0 0 true false 5 false false 0 0 true false 6 false true -101100000 -101.1 true false 7 false false 0 0 true false 8 false true -101100000 -101.1 false false No definition available. No authoritative reference available. false 32 Stock-based compensation expense: 3 us-gaap_ShareBasedCompensationAbstract us-gaap true na duration string No definition available. false false false false false true false false false 1 false false 0 0 true false 2 false false 0 0 true false 3 false false 0 0 true false 4 false false 0 0 true false 5 false false 0 0 true false 6 false false 0 0 true false 7 false false 0 0 true false 8 false false 0 0 false false No definition available. false 33 Stock units 4 us-gaap_StockIssuedDuringPeriodValueNewIssues us-gaap true credit duration monetary No definition available. false false false false false false false false false 1 false false 0 0 true false 2 false true 600000 0.6 true false 3 false false 0 0 true false 4 false false 0 0 true false 5 false false 0 0 true false 6 false true 600000 0.6 true false 7 false false 0 0 true false 8 false true 600000 0.6 false false No definition available. No authoritative reference available. false 34 Non-employee director stock awards (in shares) 4 aye_StockIssuedDuringPeriodSharesDirectorStockAward aye false na duration shares Represents the number of shares issued during the period for non-employee director stock awards. false false false false false false false false false 1 false true 20869 20869.00 true false 2 false false 0 0 true false 3 false false 0 0 true false 4 false false 0 0 true false 5 false false 0 0 true false 6 false false 0 0 true false 7 false false 0 0 true false 8 false false 0 0 false false Represents the number of shares issued during the period for non-employee director stock awards. No authoritative reference available. false 35 Non-employee director stock awards 4 aye_StockIssuedDuringPeriodValueDirectorStockAward aye false credit duration monetary Par value stock issued during the period as a result of the issuance of non-employee director stock awards. false false false false false false false false false 1 false false 0 0 true false 2 false true 1100000 1.1 true false 3 false false 0 0 true false 4 false false 0 0 true false 5 false false 0 0 true false 6 false true 1100000 1.1 true false 7 false false 0 0 true false 8 false true 1100000 1.1 false false Par value stock issued during the period as a result of the issuance of non-employee director stock awards. No authoritative reference available. false 36 Stock options 4 us-gaap_AdjustmentsToAdditionalPaidInCapitalSharebasedCompensationRequisiteServicePeriodRecognitionValue us-gaap true credit duration monetary No definition available. false false false false false false false false false 1 false false 0 0 true false 2 false true 9300000 9.3 true false 3 false false 0 0 true false 4 false false 0 0 true false 5 false false 0 0 true false 6 false true 9300000 9.3 true false 7 false false 0 0 true false 8 false true 9300000 9.3 false false No definition available. No authoritative reference available. false 37 Performance shares 4 aye_NonVestedStockUnitAndPerformanceBasedAwardCompensation aye false credit duration monetary Non-vested stock unit and performance-based award compensation. false false false false false false false false false 1 false false 0 0 true false 2 false true 2900000 2.9 true false 3 false false 0 0 true false 4 false false 0 0 true false 5 false false 0 0 true false 6 false true 2900000 2.9 true false 7 false false 0 0 true false 8 false true 2900000 2.9 false false Non-vested stock unit and performance-based award compensation. No authoritative reference available. false 40 Exercise of stock options (in shares) 3 us-gaap_StockIssuedDuringPeriodSharesStockOptionsExercised us-gaap true na duration shares No definition available. false false false false false false false false false 1 false true 1849316 1849316.00 true false 2 false false 0 0 true false 3 false false 0 0 true false 4 false false 0 0 true false 5 false false 0 0 true false 6 false false 0 0 true false 7 false false 0 0 true false 8 false false 0 0 false false No definition available. No authoritative reference available. false 41 Exercise of stock options 3 us-gaap_StockIssuedDuringPeriodValueStockOptionsExercised us-gaap true credit duration monetary No definition available. false false false false false false false false false 1 false true 2300000 2.3 true false 2 false true 23000000 23.0 true false 3 false false 0 0 true false 4 false false 0 0 true false 5 false false 0 0 true false 6 false true 25300000 25.3 true false 7 false false 0 0 true false 8 false true 25300000 25.3 false false No definition available. No authoritative reference available. false 42 Settlement of stock units (in shares) 3 aye_StockIssuedDuringPeriodSharesStockUnits aye false na duration shares Number of stock units issued. false false false false false false false false false 1 false true 270633 270633.00 true false 2 false false 0 0 true false 3 false false 0 0 true false 4 false false 0 0 true false 5 false false 0 0 true false 6 false false 0 0 true false 7 false false 0 0 true false 8 false false 0 0 false false Number of stock units issued. No authoritative reference available. false 43 Settlement of stock units 3 aye_StockIssuedDuringPeriodStockUnits aye false credit duration monetary Value stock issued during the period as a result of the settlement of stock units. false false false false false false false false false 1 false true 400000 0.4 true false 2 false true -8500000 -8.5 true false 3 false false 0 0 true false 4 false false 0 0 true false 5 false false 0 0 true false 6 false true -8100000 -8.1 true false 7 false false 0 0 true false 8 false true -8100000 -8.1 false false Value stock issued during the period as a result of the settlement of stock units. No authoritative reference available. false 45 Dividends on stock units 3 us-gaap_DividendsCash us-gaap true debit duration monetary No definition available. false false false false false false false false false 1 false false 0 0 true false 2 false false 0 0 true false 3 false true -100000 -0.1 true false 4 false false 0 0 true false 5 false false 0 0 true false 6 false true -100000 -0.1 true false 7 false false 0 0 true false 8 false true -100000 -0.1 false false No definition available. No authoritative reference available. false 47 Other 3 us-gaap_StockholdersEquityOther us-gaap true debit duration monetary No definition available. false false false false false false false false false 1 false false 0 0 true false 2 false false 0 0 true false 3 false false 0 0 true false 4 false false 0 0 true false 5 false true -100000 -0.1 true false 6 false true -100000 -0.1 true false 7 false false 0 0 true false 8 false true -100000 -0.1 false false No definition available. No authoritative reference available. false 48 Ending Balance (in shares) at Dec. 31, 2008 3 aye_SharesOutstanding aye false na instant shares Number of shares of stock held by shareholders. false false false true false false false true false 1 false true 169364394 169364394.00 true false 2 false false 0 0 true false 3 false false 0 0 true false 4 false false 0 0 true false 5 false false 0 0 true false 6 false false 0 0 true false 7 false false 0 0 true false 8 false false 0 0 false false Number of shares of stock held by shareholders. No authoritative reference available. false 49 Ending Balance at Dec. 31, 2008 3 us-gaap_StockholdersEquityIncludingPortionAttributableToNoncontrollingInterest us-gaap true credit instant monetary No definition available. false false false true false false false true false 1 false true 211800000 211.8 true false 2 false true 1952500000 1952.5 true false 3 false true 731600000 731.6 true false 4 false true -1800000 -1.8 true false 5 false true -43300000 -43.3 true false 6 false true 2850800000 2850.8 true false 7 false true 4900000 4.9 true false 8 false true 2855700000 2855.7 false false No definition available. No authoritative reference available. false 7 Net income 3 us-gaap_ProfitLoss us-gaap true credit duration monetary No definition available. false false false false false false false false false 1 false false 0 0 true false 2 false false 0 0 true false 3 false true 392800000 392.8 true false 4 false false 0 0 true false 5 false false 0 0 true false 6 false true 392800000 392.8 true false 7 false true 1300000 1.3 true false 8 false true 394100000 394.1 false false No definition available. No authoritative reference available. false 8 Defined benefit pension and other benefit plans: 3 us-gaap_OtherComprehensiveIncomeDefinedBenefitPlansAdjustmentNetOfTaxPeriodIncreaseDecreaseAbstract us-gaap true na duration string No definition available. false false false false false true false false false 1 false false 0 0 true false 2 false false 0 0 true false 3 false false 0 0 true false 4 false false 0 0 true false 5 false false 0 0 true false 6 false false 0 0 true false 7 false false 0 0 true false 8 false false 0 0 false false No definition available. false 9 Net gain (loss) during the period, net of tax of $3.1 in 2009, $(26.9) in 2008 and $10.6 in 2007 4 us-gaap_OtherComprehensiveIncomeDefinedBenefitPlansAdjustmentNetOfTaxPeriodIncreaseDecrease us-gaap true na duration monetary No definition available. false false false false false false false false false 1 false false 0 0 true false 2 false false 0 0 true false 3 false false 0 0 true false 4 false false 0 0 true false 5 false true -5300000 -5.3 true false 6 false true -5300000 -5.3 true false 7 false false 0 0 true false 8 false true -5300000 -5.3 false false No definition available. No authoritative reference available. false 10 Amortization, net of tax of $2.1 in 2009, $1.1 in 2008 and $2.4 in 2007 4 us-gaap_OtherComprehensiveIncomeAmortizationOfDefinedBenefitPlanNetPriorServiceCostRecognizedInNetPeriodicPensionCostNetOfTax us-gaap true credit duration monetary No definition available. false false false false false false false false false 1 false false 0 0 true false 2 false false 0 0 true false 3 false false 0 0 true false 4 false false 0 0 true false 5 false true 3500000 3.5 true false 6 false true 3500000 3.5 true false 7 false false 0 0 true false 8 false true 3500000 3.5 false false No definition available. No authoritative reference available. false 11 Cash flow hedges, net of tax of $28.5 in 2009, $20.5 in 2008 and $2.9 in 2007 3 us-gaap_OtherComprehensiveIncomeDerivativesQualifyingAsHedgesNetOfTaxPeriodIncreaseDecrease us-gaap true na duration monetary No definition available. false false false false false false false false false 1 false false 0 0 true false 2 false false 0 0 true false 3 false false 0 0 true false 4 false false 0 0 true false 5 false true -44800000 -44.8 true false 6 false true -44800000 -44.8 true false 7 false false 0 0 true false 8 false true -44800000 -44.8 false false No definition available. No authoritative reference available. false 12 Effects of West Virginia Rate Order: 3 aye_EffectOfRateOrderAbstract aye false na duration string Effect Of Rate Order [Abstract] false false false false false true false false false 1 false false 0 0 true false 2 false false 0 0 true false 3 false false 0 0 true false 4 false false 0 0 true false 5 false false 0 0 true false 6 false false 0 0 true false 7 false false 0 0 true false 8 false false 0 0 false false Effect Of Rate Order [Abstract] false 21 Equity contribution to PATH, LLC by the joint venture partner 3 aye_ContributionsFromNoncontrollingInterests aye false credit duration monetary Contributions from noncontrolling interests. false false false false false false false false false 1 false false 0 0 true false 2 false false 0 0 true false 3 false false 0 0 true false 4 false false 0 0 true false 5 false false 0 0 true false 6 false false 0 0 true false 7 false true 8700000 8.7 true false 8 false true 8700000 8.7 false false Contributions from noncontrolling interests. No authoritative reference available. false 26 Amortizations: 3 aye_AmortizationAbstract aye false na duration string Amortization [Abstract] false false false false false true false false false 1 false false 0 0 true false 2 false false 0 0 true false 3 false false 0 0 true false 4 false false 0 0 true false 5 false false 0 0 true false 6 false false 0 0 true false 7 false false 0 0 true false 8 false false 0 0 false false Amortization [Abstract] false 31 Dividends on common stock 3 us-gaap_DividendsCommonStock us-gaap true debit duration monetary No definition available. false false false false false false false false false 1 false false 0 0 true false 2 false false 0 0 true false 3 false true -101700000 -101.7 true false 4 false false 0 0 true false 5 false false 0 0 true false 6 false true -101700000 -101.7 true false 7 false false 0 0 true false 8 false true -101700000 -101.7 false false No definition available. No authoritative reference available. false 32 Stock-based compensation expense: 3 us-gaap_ShareBasedCompensationAbstract us-gaap true na duration string No definition available. false false false false false true false false false 1 false false 0 0 true false 2 false false 0 0 true false 3 false false 0 0 true false 4 false false 0 0 true false 5 false false 0 0 true false 6 false false 0 0 true false 7 false false 0 0 true false 8 false false 0 0 false false No definition available. false 34 Non-employee director stock awards (in shares) 4 aye_StockIssuedDuringPeriodSharesDirectorStockAward aye false na duration shares Represents the number of shares issued during the period for non-employee director stock awards. false false false false false false false false false 1 false true 21907 21907.00 true false 2 false false 0 0 true false 3 false false 0 0 true false 4 false false 0 0 true false 5 false false 0 0 true false 6 false false 0 0 true false 7 false false 0 0 true false 8 false false 0 0 false false Represents the number of shares issued during the period for non-employee director stock awards. No authoritative reference available. false 35 Non-employee director stock awards 4 aye_StockIssuedDuringPeriodValueDirectorStockAward aye false credit duration monetary Par value stock issued during the period as a result of the issuance of non-employee director stock awards. false false false false false false false false false 1 false false 0 0 true false 2 false true 900000 0.9 true false 3 false false 0 0 true false 4 false false 0 0 true false 5 false false 0 0 true false 6 false true 900000 0.9 true false 7 false false 0 0 true false 8 false true 900000 0.9 false false Par value stock issued during the period as a result of the issuance of non-employee director stock awards. No authoritative reference available. false 36 Stock options 4 us-gaap_AdjustmentsToAdditionalPaidInCapitalSharebasedCompensationRequisiteServicePeriodRecognitionValue us-gaap true credit duration monetary No definition available. false false false false false false false false false 1 false false 0 0 true false 2 false true 7400000 7.4 true false 3 false false 0 0 true false 4 false false 0 0 true false 5 false false 0 0 true false 6 false true 7400000 7.4 true false 7 false false 0 0 true false 8 false true 7400000 7.4 false false No definition available. No authoritative reference available. false 37 Performance shares 4 aye_NonVestedStockUnitAndPerformanceBasedAwardCompensation aye false credit duration monetary Non-vested stock unit and performance-based award compensation. false false false false false false false false false 1 false false 0 0 true false 2 false true 7200000 7.2 true false 3 false false 0 0 true false 4 false false 0 0 true false 5 false false 0 0 true false 6 false true 7200000 7.2 true false 7 false false 0 0 true false 8 false true 7200000 7.2 false false Non-vested stock unit and performance-based award compensation. No authoritative reference available. false 38 Restricted shares (in shares) 4 us-gaap_StockIssuedDuringPeriodSharesRestrictedStockAwardGross us-gaap true na duration shares No definition available. false false false false false false false false false 1 false true 17850 17850.00 true false 2 false false 0 0 true false 3 false false 0 0 true false 4 false false 0 0 true false 5 false false 0 0 true false 6 false false 0 0 true false 7 false false 0 0 true false 8 false false 0 0 false false No definition available. No authoritative reference available. false 39 Restricted shares 4 us-gaap_StockIssuedDuringPeriodValueRestrictedStockAwardGross us-gaap true credit duration monetary No definition available. false false false false false false false false false 1 false false 0 0 true false 2 false true 100000 0.1 true false 3 false false 0 0 true false 4 false false 0 0 true false 5 false false 0 0 true false 6 false true 100000 0.1 true false 7 false false 0 0 true false 8 false true 100000 0.1 false false No definition available. No authoritative reference available. false 40 Exercise of stock options (in shares) 3 us-gaap_StockIssuedDuringPeriodSharesStockOptionsExercised us-gaap true na duration shares No definition available. false false false false false false false false false 1 false true 163700 163700.00 true false 2 false false 0 0 true false 3 false false 0 0 true false 4 false false 0 0 true false 5 false false 0 0 true false 6 false false 0 0 true false 7 false false 0 0 true false 8 false false 0 0 false false No definition available. No authoritative reference available. false 41 Exercise of stock options 3 us-gaap_StockIssuedDuringPeriodValueStockOptionsExercised us-gaap true credit duration monetary No definition available. false false false false false false false false false 1 false true 200000 0.2 true false 2 false true 2100000 2.1 true false 3 false false 0 0 true false 4 false false 0 0 true false 5 false false 0 0 true false 6 false true 2300000 2.3 true false 7 false false 0 0 true false 8 false true 2300000 2.3 false false No definition available. No authoritative reference available. false 42 Settlement of stock units (in shares) 3 aye_StockIssuedDuringPeriodSharesStockUnits aye false na duration shares Number of stock units issued. false false false false false false false false false 1 false true 3573 3573.00 true false 2 false false 0 0 true false 3 false false 0 0 true false 4 false false 0 0 true false 5 false false 0 0 true false 6 false false 0 0 true false 7 false false 0 0 true false 8 false false 0 0 false false Number of stock units issued. No authoritative reference available. false 44 Treasury stock 3 us-gaap_TreasuryStockSharesAcquired us-gaap true na duration shares No definition available. false false false false false false false false false 1 false true -1820 -1820.00 true false 2 false false 0 0 true false 3 false false 0 0 true false 4 false false 0 0 true false 5 false false 0 0 true false 6 false false 0 0 true false 7 false false 0 0 true false 8 false false 0 0 false false No definition available. No authoritative reference available. false 48 Ending Balance (in shares) at Dec. 31, 2009 3 aye_SharesOutstanding aye false na instant shares Number of shares of stock held by shareholders. false false false true false false false true false 1 false true 169569604 169569604.00 true false 2 false false 0 0 true false 3 false false 0 0 true false 4 false false 0 0 true false 5 false false 0 0 true false 6 false false 0 0 true false 7 false false 0 0 true false 8 false false 0 0 false false Number of shares of stock held by shareholders. No authoritative reference available. false 49 Ending Balance at Dec. 31, 2009 3 us-gaap_StockholdersEquityIncludingPortionAttributableToNoncontrollingInterest us-gaap true credit instant monetary No definition available. false false false true false false false true false 1 true true 212000000 212.0 true false 2 true true 1970200000 1970.2 true false 3 true true 1022700000 1022.7 true false 4 true true -1800000 -1.8 true false 5 true true -89900000 -89.9 true false 6 true true 3113200000 3113.2 true false 7 true true 14900000 14.9 true false 8 true true 3128100000 3128.1 false false No definition available. No authoritative reference available. false false 8 82 false HundredThousands NoRounding UnKnown false true