1.0.0.3 false Statement Of Financial Position Classified (USD $) In Thousands false 1 $ false false Shares Standard http://www.xbrl.org/2003/instance shares 0 USD Standard http://www.xbrl.org/2003/iso4217 USD iso4217 0 USDperShareItemType Divide http://www.xbrl.org/2003/iso4217 USD iso4217 http://www.xbrl.org/2003/instance shares 0 false 2 $ false false Shares Standard http://www.xbrl.org/2003/instance shares 0 USD Standard http://www.xbrl.org/2003/iso4217 USD iso4217 0 USDperShareItemType Divide http://www.xbrl.org/2003/iso4217 USD iso4217 http://www.xbrl.org/2003/instance shares 0 6 Current Assets: 4 us-gaap_AssetsCurrentAbstract 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 No definition available. false 7 Cash and cash equivalents 5 us-gaap_CashAndCashEquivalentsAtCarryingValue us-gaap true debit instant monetary No definition available. false false false false false false false false false 1 true true 232038000 232038 false false 2 true true 362145000 362145 false false No definition available. No authoritative reference available. false 8 Accounts receivable: 5 us-gaap_AccountsReceivableNetCurrentAbstract 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 No definition available. false 9 Customer 6 us-gaap_AccountsReceivableGrossCurrent us-gaap true debit instant monetary No definition available. false false false false false false false false false 1 false true 201044000 201044 false false 2 false true 188309000 188309 false false No definition available. No authoritative reference available. false 10 Unbilled utility revenue 6 us-gaap_ReceivablesLongTermContractsOrPrograms us-gaap true debit instant monetary No definition available. false false false false false false false false false 1 false true 88135000 88135 false false 2 false true 122695000 122695 false false No definition available. No authoritative reference available. false 11 Wholesale and other 6 us-gaap_OtherReceivables us-gaap true debit instant monetary No definition available. false false false false false false false false false 1 false true 71357000 71357 false false 2 false true 61445000 61445 false false No definition available. No authoritative reference available. false 12 Allowance for uncollectible accounts 6 us-gaap_AllowanceForDoubtfulAccountsReceivableCurrent us-gaap true credit instant monetary No definition available. false false false false false false false false false 1 false true -13870000 -13870 false false 2 false true -13280000 -13280 false false No definition available. No authoritative reference available. false 13 Materials and supplies 6 us-gaap_InventoryNet us-gaap true debit instant monetary No definition available. false false false false false false false false false 1 false true 111794000 111794 false false 2 false true 115107000 115107 false false No definition available. No authoritative reference available. false 14 Fuel 6 us-gaap_EnergyRelatedInventory us-gaap true debit instant monetary No definition available. false false false false false false false false false 1 false true 206561000 206561 false false 2 false true 128238000 128238 false false No definition available. No authoritative reference available. false 15 Deferred income taxes 6 us-gaap_DeferredTaxAssetsNetCurrent us-gaap true debit instant monetary No definition available. false false false false false false false false false 1 false true 46026000 46026 false false 2 false true 69617000 69617 false false No definition available. No authoritative reference available. false 16 Prepaid taxes 6 us-gaap_PrepaidTaxes us-gaap true debit instant monetary No definition available. false false false false false false false false false 1 false true 56387000 56387 false false 2 false true 44766000 44766 false false No definition available. No authoritative reference available. false 17 Collateral deposits 6 us-gaap_DepositAssets us-gaap true debit instant monetary No definition available. false false false false false false false false false 1 false true 49349000 49349 false false 2 false true 33441000 33441 false false No definition available. No authoritative reference available. false 18 Derivative assets 6 us-gaap_DerivativeAssetsCurrent us-gaap true debit instant monetary No definition available. false false false false false false false false false 1 false true 108415000 108415 false false 2 false true 113087000 113087 false false No definition available. No authoritative reference available. false 19 Regulatory assets 6 us-gaap_RegulatoryAssetsCurrent us-gaap true debit instant monetary No definition available. false false false false false false false false false 1 false true 146759000 146759 false false 2 false true 158835000 158835 false false No definition available. No authoritative reference available. false 20 Assets held for sale 6 us-gaap_AssetsHeldForSaleCurrent us-gaap true debit instant monetary No definition available. false false false false false false false false false 1 false true 30144000 30144 false false 2 false true 0 0 false false No definition available. No authoritative reference available. false 21 Other 6 us-gaap_OtherAssetsCurrent us-gaap true debit instant monetary No definition available. false false false false false false false false false 1 false true 70011000 70011 false false 2 false true 111317000 111317 false false No definition available. No authoritative reference available. false 22 Total current assets 5 us-gaap_AssetsCurrent us-gaap true debit instant monetary No definition available. false false false false false false false false false 1 false true 1404150000 1404150 false false 2 false true 1495722000 1495722 false false No definition available. No authoritative reference available. true 23 Property, Plant and Equipment: 4 us-gaap_PropertyPlantAndEquipmentNetAbstract 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 No definition available. false 24 Generation 5 aye_PropertyPlantAndEquipmentGenerationOrProcessing aye false debit instant monetary No definition available. false false false false false false false false false 1 false true 6621037000 6621037 false false 2 false true 6107344000 6107344 false false No definition available. No authoritative reference available. false 25 Transmission 5 us-gaap_PublicUtilitiesPropertyPlantAndEquipmentTransmission us-gaap true debit instant monetary No definition available. false false false false false false false false false 1 false true 1222881000 1222881 false false 2 false true 1171716000 1171716 false false No definition available. No authoritative reference available. false 26 Distribution 5 us-gaap_PublicUtilitiesPropertyPlantAndEquipmentDistribution us-gaap true debit instant monetary No definition available. false false false false false false false false false 1 false true 3693298000 3693298 false false 2 false true 3944068000 3944068 false false No definition available. No authoritative reference available. false 27 Other 5 us-gaap_PropertyPlantAndEquipmentOther us-gaap true debit instant monetary No definition available. false false false false false false false false false 1 false true 462692000 462692 false false 2 false true 463377000 463377 false false No definition available. No authoritative reference available. false 28 Accumulated depreciation 5 us-gaap_AccumulatedDepreciationDepletionAndAmortizationPropertyPlantAndEquipment us-gaap true credit instant monetary No definition available. false false false false false false false false false 1 false true -4995338000 -4995338 false false 2 false true -4994099000 -4994099 false false No definition available. No authoritative reference available. false 29 Subtotal 5 us-gaap_PublicUtilitiesPropertyPlantAndEquipmentNet us-gaap true debit instant monetary No definition available. false false false false false false false false false 1 false true 7004570000 7004570 false false 2 false true 6692406000 6692406 false false No definition available. No authoritative reference available. true 30 Construction work in progress 5 us-gaap_ConstructionInProgressGross us-gaap true debit instant monetary No definition available. false false false false false false false false false 1 false true 1202030000 1202030 false false 2 false true 1309790000 1309790 false false No definition available. No authoritative reference available. false 31 Property, plant and equipment held for sale, net 5 us-gaap_AssetsHeldForSalePropertyPlantAndEquipment us-gaap true debit instant monetary No definition available. false false false false false false false false false 1 false true 249065000 249065 false false 2 false true 0 0 false false No definition available. No authoritative reference available. false 32 Total property, plant and equipment, net 5 us-gaap_PropertyPlantAndEquipmentNet us-gaap true debit instant monetary No definition available. false false false false false false false false false 1 false true 8455665000 8455665 false false 2 false true 8002196000 8002196 false false No definition available. No authoritative reference available. true 33 Investments and Other Assets: 4 aye_InvestmentsAndOtherAssetsAbstract aye false 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 No definition available. false 34 Goodwill 5 us-gaap_Goodwill us-gaap true debit instant monetary No definition available. false false false false false false false false false 1 false true 367287000 367287 false false 2 false true 367287000 367287 false false No definition available. No authoritative reference available. false 35 Restricted funds-Fort Martin scrubber project 5 us-gaap_RestrictedCashAndCashEquivalentsNoncurrent us-gaap true debit instant monetary No definition available. false false false false false false false false false 1 false true 33642000 33642 false false 2 false true 133346000 133346 false false No definition available. No authoritative reference available. false 36 Investments in unconsolidated affiliates 5 us-gaap_InvestmentsInAffiliatesSubsidiariesAssociatesAndJointVentures us-gaap true debit instant monetary No definition available. false false false false false false false false false 1 false true 27132000 27132 false false 2 false true 27955000 27955 false false No definition available. No authoritative reference available. false 37 Other 5 us-gaap_OtherAssetsNoncurrent us-gaap true debit instant monetary No definition available. false false false false false false false false false 1 false true 21221000 21221 false false 2 false true 19695000 19695 false false No definition available. No authoritative reference available. false 38 Total investments and other assets 5 aye_TotalInvestmentsAndOtherAssets aye false debit instant monetary No definition available. false false false false false false false false false 1 false true 449282000 449282 false false 2 false true 548283000 548283 false false No definition available. No authoritative reference available. true 39 Deferred Charges: 4 us-gaap_DeferredCostsAbstract 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 No definition available. false 40 Regulatory assets 5 us-gaap_RegulatoryAssetsNoncurrent us-gaap true debit instant monetary No definition available. false false false false false false false false false 1 false true 668277000 668277 false false 2 false true 687696000 687696 false false No definition available. No authoritative reference available. false 41 Derivative assets 5 us-gaap_DerivativeAssetsNoncurrent us-gaap true debit instant monetary No definition available. false false false false false false false false false 1 false true 5691000 5691 false false 2 false true 9816000 9816 false false No definition available. No authoritative reference available. false 42 Assets held for sale 5 us-gaap_AssetsHeldForSaleLongLived us-gaap true debit instant monetary No definition available. false false false false false false false false false 1 false true 52000 52 false false 2 false true 0 0 false false No definition available. No authoritative reference available. false 43 Other 5 us-gaap_OtherDeferredCostsNet us-gaap true debit instant monetary No definition available. false false false false false false false false false 1 false true 64587000 64587 false false 2 false true 67335000 67335 false false No definition available. No authoritative reference available. false 44 Total deferred charges 5 aye_DeferredChargesRegulatoryAssetsAndOtherAssetsNoncurrent aye false debit instant monetary No definition available. false false false false false false false false false 1 false true 738607000 738607 false false 2 false true 764847000 764847 false false No definition available. No authoritative reference available. true 45 Total Assets 4 us-gaap_Assets us-gaap true debit instant monetary No definition available. false false false false false false false false false 1 false true 11047704000 11047704 false false 2 false true 10811048000 10811048 false false No definition available. No authoritative reference available. true 47 Current Liabilities: 4 us-gaap_LiabilitiesCurrentAbstract 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 No definition available. false 48 Long-term debt due within one year 5 us-gaap_LongTermDebtCurrent us-gaap true credit instant monetary No definition available. false false false false false false false false false 1 false true 179669000 179669 false false 2 false true 93848000 93848 false false No definition available. No authoritative reference available. false 49 Accounts payable 5 us-gaap_AccountsPayable us-gaap true credit instant monetary No definition available. false false false false false false false false false 1 false true 378998000 378998 false false 2 false true 374229000 374229 false false No definition available. No authoritative reference available. false 50 Accrued taxes 5 us-gaap_TaxesPayable us-gaap true credit instant monetary No definition available. false false false false false false false false false 1 false true 48253000 48253 false false 2 false true 119431000 119431 false false No definition available. No authoritative reference available. false 51 Payable to PJM for FTRs 5 us-gaap_AccountsPayableOther us-gaap true credit instant monetary No definition available. false false false false false false false false false 1 false true 34433000 34433 false false 2 false true 110774000 110774 false false No definition available. No authoritative reference available. false 52 Derivative liabilities 5 us-gaap_DerivativeLiabilitiesCurrent us-gaap true credit instant monetary No definition available. false false false false false false false false false 1 false true 14409000 14409 false false 2 false true 22153000 22153 false false No definition available. No authoritative reference available. false 53 Regulatory liabilities 5 us-gaap_RegulatoryLiabilityCurrent us-gaap true credit instant monetary No definition available. false false false false false false false false false 1 false true 45143000 45143 false false 2 false true 69208000 69208 false false No definition available. No authoritative reference available. false 54 Accrued interest 5 us-gaap_InterestPayable us-gaap true credit instant monetary No definition available. false false false false false false false false false 1 false true 56531000 56531 false false 2 false true 58048000 58048 false false No definition available. No authoritative reference available. false 55 Security deposits 5 us-gaap_CustomerDepositsCurrent us-gaap true credit instant monetary No definition available. false false false false false false false false false 1 false true 46676000 46676 false false 2 false true 46166000 46166 false false No definition available. No authoritative reference available. false 56 Liabilities associated with assets held for sale 5 aye_LiabilitiesOfAssetsHeldForSaleCurrent aye false credit instant monetary No definition available. false false false false false false false false false 1 false true 12724000 12724 false false 2 false true 0 0 false false No definition available. No authoritative reference available. false 57 Other 5 us-gaap_OtherLiabilitiesCurrent us-gaap true credit instant monetary No definition available. false false false false false false false false false 1 false true 107086000 107086 false false 2 false true 109643000 109643 false false No definition available. No authoritative reference available. false 58 Total current liabilities 5 us-gaap_LiabilitiesCurrent us-gaap true credit instant monetary No definition available. false false false false false false false false false 1 false true 923922000 923922 false false 2 false true 1003500000 1003500 false false No definition available. No authoritative reference available. true 59 Long-term Debt, excluding amounts due within one year 4 us-gaap_LongTermDebtNoncurrent us-gaap true credit instant monetary No definition available. false false false false false false false false false 1 false true 4143539000 4143539 false false 2 false true 4115921000 4115921 false false No definition available. No authoritative reference available. false 60 Deferred Credits and Other Liabilities: 4 aye_TotalDeferredCreditsAndOtherLiabilitiesAbstract aye false 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 No definition available. false 61 Derivative liabilities 5 us-gaap_DerivativeLiabilitiesNoncurrent us-gaap true credit instant monetary No definition available. false false false false false false false false false 1 false true 9228000 9228 false false 2 false true 11886000 11886 false false No definition available. No authoritative reference available. false 62 Income taxes payable 5 aye_IncomeTaxesPayableNoncurrent aye false credit instant monetary No definition available. false false false false false false false false false 1 false true 81759000 81759 false false 2 false true 75669000 75669 false false No definition available. No authoritative reference available. false 63 Investment tax credit 5 us-gaap_AccumulatedDeferredInvestmentTaxCredit us-gaap true credit instant monetary No definition available. false false false false false false false false false 1 false true 63679000 63679 false false 2 false true 65768000 65768 false false No definition available. No authoritative reference available. false 64 Deferred income taxes 5 us-gaap_DeferredTaxLiabilitiesNoncurrent us-gaap true credit instant monetary No definition available. false false false false false false false false false 1 false true 1370602000 1370602 false false 2 false true 1277439000 1277439 false false No definition available. No authoritative reference available. false 65 Regulatory liabilities 5 us-gaap_RegulatoryLiabilityNoncurrent us-gaap true credit instant monetary No definition available. false false false false false false false false false 1 false true 474185000 474185 false false 2 false true 528937000 528937 false false No definition available. No authoritative reference available. false 66 Pension and other postretirement employee benefit plan liabilities 5 us-gaap_PensionAndOtherPostretirementDefinedBenefitPlansNoncurrentLiabilities us-gaap true credit instant monetary No definition available. false false false false false false false false false 1 false true 591483000 591483 false false 2 false true 578440000 578440 false false No definition available. No authoritative reference available. false 67 Adverse power purchase commitment 5 us-gaap_LiabilityAboveMarketForNonutilityGeneratorContractsNoncurrent us-gaap true credit instant monetary No definition available. false false false false false false false false false 1 false true 123379000 123379 false false 2 false true 132334000 132334 false false No definition available. No authoritative reference available. false 68 Liabilities associated with assets held for sale 5 aye_LiabilitiesOfAssetsHeldForSaleNoncurrent aye false credit instant monetary No definition available. false false false false false false false false false 1 false true 54137000 54137 false false 2 false true 0 0 false false No definition available. No authoritative reference available. false 69 Other 5 us-gaap_OtherLiabilitiesNoncurrent us-gaap true credit instant monetary No definition available. false false false false false false false false false 1 false true 160536000 160536 false false 2 false true 165500000 165500 false false No definition available. No authoritative reference available. false 70 Total deferred credits and other liabilities 5 aye_TotalDeferredCreditsAndOtherLiabilities aye false credit instant monetary No definition available. false false false false false false false false false 1 false true 2928988000 2928988 false false 2 false true 2835973000 2835973 false false No definition available. No authoritative reference available. true 71 Commitments and Contingencies (Note 15) 4 us-gaap_CommitmentsAndContingencies us-gaap true credit instant monetary No definition available. false false false false false false false false false 1 false true 0 0 false false 2 false true 0 0 false false No definition available. No authoritative reference available. false 72 Equity: 4 aye_StockholdersEquityIncludingPortionAttributableToNoncontrollingInterestAbstract aye false 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 No definition available. false 73 Common stock-$1.25 par value per share, 260 million shares authorized and 169,532,084 and 169,413,887 shares issued at June 30, 2009 and December 31, 2008, respectively 5 us-gaap_CommonStockValue us-gaap true credit instant monetary No definition available. false false false false false false false false false 1 false true 211893000 211893 false false 2 false true 211767000 211767 false false No definition available. No authoritative reference available. false 74 Other paid-in capital 5 us-gaap_AdditionalPaidInCapitalCommonStock us-gaap true credit instant monetary No definition available. false false false false false false false false false 1 false true 1981875000 1981875 false false 2 false true 1952440000 1952440 false false No definition available. No authoritative reference available. false 75 Retained earnings 5 us-gaap_RetainedEarningsAccumulatedDeficit us-gaap true credit instant monetary No definition available. false false false false false false false false false 1 false true 887298000 887298 false false 2 false true 731615000 731615 false false No definition available. No authoritative reference available. false 76 Treasury stock at cost-49,493 shares 5 us-gaap_TreasuryStockValue us-gaap true debit instant monetary No definition available. false false false false false false false false false 1 false true -1756000 -1756 false false 2 false true -1756000 -1756 false false No definition available. No authoritative reference available. false 77 Accumulated other comprehensive loss 5 us-gaap_AccumulatedOtherComprehensiveIncomeLossNetOfTax us-gaap true credit instant monetary No definition available. false false false false false false false false false 1 false true -33610000 -33610 false false 2 false true -43318000 -43318 false false No definition available. No authoritative reference available. false 78 Total Allegheny Energy, Inc. common stockholders' equity 5 us-gaap_StockholdersEquity us-gaap true credit instant monetary No definition available. false false false false false false false false false 1 false true 3045700000 3045700 false false 2 false true 2850748000 2850748 false false No definition available. No authoritative reference available. true 79 Noncontrolling interest 4 us-gaap_MinorityInterest us-gaap true credit instant monetary No definition available. false false false false false false false false false 1 false true 5555000 5555 false false 2 false true 4906000 4906 false false No definition available. No authoritative reference available. false 80 Total equity 4 aye_StockholdersEquityIncludingPortionAttributableToNoncontrollingInterest aye false credit instant monetary No definition available. false false false false false false false false false 1 false true 3051255000 3051255 false false 2 false true 2855654000 2855654 false false No definition available. No authoritative reference available. true 81 Total Liabilities and Equity 4 us-gaap_LiabilitiesAndStockholdersEquity us-gaap true credit instant monetary No definition available. false false false false false false false false false 1 true true 11047704000 11047704 false false 2 true true 10811048000 10811048 false false No definition available. No authoritative reference available. true false 2 75 false Thousands UnKnown UnKnown false true