1.0.0.3 true CONSOLIDATED STATEMENTS OF COMMON SHAREHOLDERS' EQUITY AND COMPREHENSIVE INCOME (LOSS) (Constellation Energy Group, Inc. and Subsidiaries) (USD $) In Millions, except Share data in Thousands false 1 $ true false false false Common Stock us-gaap_StatementEquityComponentsAxis xbrldi http://xbrl.org/2006/xbrldi us-gaap_CommonStockMember us-gaap_StatementEquityComponentsAxis explicitMember Shares Standard http://www.xbrl.org/2003/instance shares xbrli 0 USD Standard http://www.xbrl.org/2003/iso4217 USD iso4217 0 false 2 $ true false false false Retained Earnings us-gaap_StatementEquityComponentsAxis xbrldi http://xbrl.org/2006/xbrldi us-gaap_RetainedEarningsMember us-gaap_StatementEquityComponentsAxis explicitMember USD Standard http://www.xbrl.org/2003/iso4217 USD iso4217 0 false 3 $ true false false false Accumulated Other Comprehensive Loss us-gaap_StatementEquityComponentsAxis xbrldi http://xbrl.org/2006/xbrldi us-gaap_AccumulatedOtherComprehensiveIncomeMember us-gaap_StatementEquityComponentsAxis explicitMember USD Standard http://www.xbrl.org/2003/iso4217 USD iso4217 0 false 4 $ true false false false Noncontrolling Interests us-gaap_StatementEquityComponentsAxis xbrldi http://xbrl.org/2006/xbrldi us-gaap_NoncontrollingInterestMember us-gaap_StatementEquityComponentsAxis explicitMember USD Standard http://www.xbrl.org/2003/iso4217 USD iso4217 0 false 5 $ false false Shares Standard http://www.xbrl.org/2003/instance shares xbrli 0 USD Standard http://www.xbrl.org/2003/iso4217 USD iso4217 0 USDPerShare Divide http://www.xbrl.org/2003/iso4217 USD iso4217 http://www.xbrl.org/2003/instance shares xbrli 0 5 Balance (in shares) at Dec. 31, 2006 2 us-gaap_CommonStockSharesOutstanding us-gaap true na instant shares No definition available. false false false true false false true false false 1 false true 180519000 180519 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 false false No definition available. No authoritative reference available. false 4 Balance at Dec. 31, 2006 2 us-gaap_StockholdersEquityIncludingPortionAttributableToNoncontrollingInterest us-gaap true credit instant monetary No definition available. false false false true false false true false false 1 true true 2738600000 2738.6 true false 2 true true 3474300000 3474.3 true false 3 true true -1603600000 -1603.6 true false 4 true true 284500000 284.5 true false 5 true true 4893800000 4893.8 false false No definition available. No authoritative reference available. false 8 Decrease in noncontrolling interests from deconsolidation 2 ceg_NoncontrollingInterestDecreaseFromDeconsolidation ceg false debit duration monetary Decrease in noncontrolling interest balance as a result of deconsolidating a subsidiary. 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 true -74100000 -74.1 true false 5 false true -74100000 -74.1 false false Decrease in noncontrolling interest balance as a result of deconsolidating a subsidiary. No authoritative reference available. false 10 Comprehensive Income (Loss) 2 us-gaap_ComprehensiveIncomeNetOfTaxIncludingPortionAttributableToNoncontrollingInterestAbstract 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 false false No definition available. false 11 Net income (loss) 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 true 821500000 821.5 true false 3 false false 0 0 true false 4 false true 12000000 12.0 true false 5 false true 833500000 833.5 false false No definition available. No authoritative reference available. false 13 Hedging instruments: 4 us-gaap_OtherComprehensiveIncomeDerivativesQualifyingAsHedgesNetOfTaxPeriodIncreaseDecreaseAbstract 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 false false No definition available. false 14 Reclassification of net losses on hedging instruments from OCI to net income, net of taxes of $(898.5), $(120.2) and $(682.3) during 2009, 2008 and 2007, respectively 5 us-gaap_OtherComprehensiveIncomeReclassificationAdjustmentOnDerivativesIncludedInNetIncomeNetOfTax 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 1124800000 1124.8 true false 4 false false 0 0 true false 5 false true 1124800000 1124.8 false false No definition available. No authoritative reference available. false 15 Net unrealized loss on hedging instruments, net of taxes of $251.2, $561.6 and $408.2 during 2009, 2008 and 2007, respectively 5 us-gaap_OtherComprehensiveIncomeUnrealizedGainLossOnDerivativesArisingDuringPeriodNetOfTax 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 -671100000 -671.1 true false 4 false false 0 0 true false 5 false true -671100000 -671.1 false false No definition available. No authoritative reference available. false 16 Available-for-sale securities: 4 us-gaap_OtherComprehensiveIncomeAvailableForSaleSecuritiesAdjustmentNetOfTaxPeriodIncreaseDecreaseAbstract 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 false false No definition available. false 17 Reclassification of net gains (losses) on securities from OCI to net income, net of taxes of $(24.6), $(79.1) and $1.0 during 2009, 2008 and 2007, respectively 5 us-gaap_OtherComprehensiveIncomeReclassificationAdjustmentForSaleOfSecuritiesIncludedInNetIncomeNetOfTax 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 -1600000 -1.6 true false 4 false false 0 0 true false 5 false true -1600000 -1.6 false false No definition available. No authoritative reference available. false 18 Net unrealized (gains) losses on securities, net of taxes of $(78.2), $189.8 and $(25.5) during 2009, 2008 and 2007, respectively 5 us-gaap_OtherComprehensiveIncomeUnrealizedHoldingGainLossOnSecuritiesArisingDuringPeriodNetOfTax 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 26500000 26.5 true false 4 false false 0 0 true false 5 false true 26500000 26.5 false false No definition available. No authoritative reference available. false 19 Defined benefit plans: 4 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 false false No definition available. false 21 Net (gain) loss arising during period, net of taxes of $(23.9), $229.2 and $(7.8) during 2009, 2008 and 2007, respectively 5 us-gaap_OtherComprehensiveIncomeDefinedBenefitPlansNetUnamortizedGainLossArisingDuringPeriodNetOfTax 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 11600000 11.6 true false 4 false false 0 0 true false 5 false true 11600000 11.6 false false No definition available. No authoritative reference available. false 22 Amortization of net actuarial loss, prior service cost, and transition obligation included in net periodic benefit cost, net of taxes of $(19.8), $(14.9) and $(15.9) during 2009, 2008 and 2007, respectively 5 ceg_OtherComprehensiveIncomeAmortizationOfNetActuarialLossPriorServiceCostAndTransitionObligationRecognizedInNetPeriodicPensionCostNetOfTax ceg false credit duration monetary The adjustment to other comprehensive income for amortization of net actuarial loss, prior service cost and transition... 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 24600000 24.6 true false 4 false false 0 0 true false 5 false true 24600000 24.6 false false The adjustment to other comprehensive income for amortization of net actuarial loss, prior service cost and transition obligation recognized as a component of net periodic benefit cost during the period, after tax. No authoritative reference available. false 23 Deconsolidation of CENG joint venture: 4 ceg_DeconsolidationOfJointVentureAbstract ceg false 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 false false No definition available. false 26 Net unrealized (gains) losses on foreign currency translation, net of taxes of $(2.7), $0.1 and $(1.8) during 2009, 2008 and 2007, respectively 4 us-gaap_OtherComprehensiveIncomeForeignCurrencyTransactionAndTranslationAdjustmentNetOfTaxPeriodIncreaseDecrease 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 true 7000000 7.0 true false 4 false false 0 0 true false 5 false true 7000000 7.0 false false No definition available. No authoritative reference available. false 29 Other 3 ceg_OtherComprehensiveIncomeOtherAdjustmentsNetOfTax ceg false credit duration monetary This element represents other adjustments to accumulated comprehensive income during the period, after tax, not otherwise... 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 -10800000 -10.8 true false 4 false false 0 0 true false 5 false true -10800000 -10.8 false false This element represents other adjustments to accumulated comprehensive income during the period, after tax, not otherwise specified in the taxonomy. No authoritative reference available. false 30 Total Comprehensive Income (Loss) 3 us-gaap_ComprehensiveIncomeNetOfTaxIncludingPortionAttributableToNoncontrollingInterest 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 821500000 821.5 true false 3 false true 511000000 511.0 true false 4 false true 12000000 12.0 true false 5 false true 1344500000 1344.5 false false No definition available. No authoritative reference available. true 31 Effect of adoption of uncertain tax position accounting standard 2 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 true -7300000 -7.3 true false 3 false false 0 0 true false 4 false false 0 0 true false 5 false true -7300000 -7.3 false false No definition available. No authoritative reference available. false 33 BGE preference stock dividends 2 us-gaap_DividendsPreferredStockCash 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 true -13200000 -13.2 true false 5 false true -13200000 -13.2 false false No definition available. No authoritative reference available. false 34 Common stock dividend declared ($0.96, $1.91 and $1.74 per share during 2009, 2008 and 2007, respectively) 2 us-gaap_DividendsCommonStockCash 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 -368400000 -368.4 true false 3 false false 0 0 true false 4 false false 0 0 true false 5 false true -368400000 -368.4 false false No definition available. No authoritative reference available. false 35 Common stock issued and share-based awards 2 ceg_StockIssuedDuringPeriodValueCommonStockIssuedAndShareBasedAwards ceg false credit duration monetary Value of new stock during the period and equity impact of any share-based compensation plan. false false false false false false false false false 1 false true 184200000 184.2 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 184200000 184.2 false false Value of new stock during the period and equity impact of any share-based compensation plan. No authoritative reference available. false 36 Common stock issued and share-based awards (in shares) 3 ceg_StockIssuedDuringPeriodSharesCommonStockIssuedAndShareBasedAwards ceg false na duration shares Number of shares of new stock issued during the period and number of shares issued during the period as a result of any... false false false false false false false false false 1 false true 1789000 1789 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 false false Number of shares of new stock issued during the period and number of shares issued during the period as a result of any share-based compensation plan. No authoritative reference available. false 37 Common stock purchased 2 us-gaap_StockRepurchasedDuringPeriodValue us-gaap true debit duration monetary No definition available. false false false false false false false false false 1 false true -159500000 -159.5 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 -159500000 -159.5 false false No definition available. No authoritative reference available. false 38 Common stock purchased (in shares) 3 us-gaap_StockRepurchasedDuringPeriodShares us-gaap true na duration shares No definition available. false false false false false false false false false 1 false true -1847000 -1847 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 false false No definition available. No authoritative reference available. false 39 Common stock purchased and retired 2 us-gaap_StockRepurchasedAndRetiredDuringPeriodValue us-gaap true debit duration monetary No definition available. false false false false false false false false false 1 false true -250000000 -250.0 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 -250000000 -250.0 false false No definition available. No authoritative reference available. false 40 Common stock purchased and retired (in shares) 3 us-gaap_StockRepurchasedAndRetiredDuringPeriodShares us-gaap true na duration shares No definition available. false false false false false false false false false 1 false true -2024000 -2024 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 false false No definition available. No authoritative reference available. false 41 Other 2 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 true -600000 -0.6 true false 3 false false 0 0 true false 4 false false 0 0 true false 5 false true -600000 -0.6 false false No definition available. No authoritative reference available. false 42 Balance at Dec. 31, 2007 2 us-gaap_StockholdersEquityIncludingPortionAttributableToNoncontrollingInterest us-gaap true credit instant monetary No definition available. false false false true false false false true false 1 false true 2513300000 2513.3 true false 2 false true 3919500000 3919.5 true false 3 false true -1092600000 -1092.6 true false 4 false true 209200000 209.2 true false 5 false true 5549400000 5549.4 false false No definition available. No authoritative reference available. false 43 Balance (in shares) at Dec. 31, 2007 2 us-gaap_CommonStockSharesOutstanding us-gaap true na instant shares No definition available. false false false true false false false true false 1 false true 178437000 178437 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 false false No definition available. No authoritative reference available. false 9 Increase in noncontrolling interests from consolidation of a VIE 2 ceg_IncreaseDecreaseInNoncontrollingInterestsFromConsolidationOfAVariableInterestEntity ceg false credit duration monetary Increase/decrease in balance of noncontrolling interest due to consolidation/deconsolidation of a variable interest entity... 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 true 18100000 18.1 true false 5 false true 18100000 18.1 false false Increase/decrease in balance of noncontrolling interest due to consolidation/deconsolidation of a variable interest entity during the period. A modification of contractual arrangements changed the allocation of economic risks and rewards of the variable interest entity among the variable interest holders. No authoritative reference available. false 10 Comprehensive Income (Loss) 2 us-gaap_ComprehensiveIncomeNetOfTaxIncludingPortionAttributableToNoncontrollingInterestAbstract 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 false false No definition available. false 11 Net income (loss) 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 true -1314400000 -1314.4 true false 3 false false 0 0 true false 4 false true -4000000 -4.0 true false 5 false true -1318400000 -1318.4 false false No definition available. No authoritative reference available. false 13 Hedging instruments: 4 us-gaap_OtherComprehensiveIncomeDerivativesQualifyingAsHedgesNetOfTaxPeriodIncreaseDecreaseAbstract 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 false false No definition available. false 14 Reclassification of net losses on hedging instruments from OCI to net income, net of taxes of $(898.5), $(120.2) and $(682.3) during 2009, 2008 and 2007, respectively 5 us-gaap_OtherComprehensiveIncomeReclassificationAdjustmentOnDerivativesIncludedInNetIncomeNetOfTax 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 200600000 200.6 true false 4 false false 0 0 true false 5 false true 200600000 200.6 false false No definition available. No authoritative reference available. false 15 Net unrealized loss on hedging instruments, net of taxes of $251.2, $561.6 and $408.2 during 2009, 2008 and 2007, respectively 5 us-gaap_OtherComprehensiveIncomeUnrealizedGainLossOnDerivativesArisingDuringPeriodNetOfTax 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 -875300000 -875.3 true false 4 false false 0 0 true false 5 false true -875300000 -875.3 false false No definition available. No authoritative reference available. false 16 Available-for-sale securities: 4 us-gaap_OtherComprehensiveIncomeAvailableForSaleSecuritiesAdjustmentNetOfTaxPeriodIncreaseDecreaseAbstract 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 false false No definition available. false 17 Reclassification of net gains (losses) on securities from OCI to net income, net of taxes of $(24.6), $(79.1) and $1.0 during 2009, 2008 and 2007, respectively 5 us-gaap_OtherComprehensiveIncomeReclassificationAdjustmentForSaleOfSecuritiesIncludedInNetIncomeNetOfTax 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 81700000 81.7 true false 4 false false 0 0 true false 5 false true 81700000 81.7 false false No definition available. No authoritative reference available. false 18 Net unrealized (gains) losses on securities, net of taxes of $(78.2), $189.8 and $(25.5) during 2009, 2008 and 2007, respectively 5 us-gaap_OtherComprehensiveIncomeUnrealizedHoldingGainLossOnSecuritiesArisingDuringPeriodNetOfTax 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 -197500000 -197.5 true false 4 false false 0 0 true false 5 false true -197500000 -197.5 false false No definition available. No authoritative reference available. false 19 Defined benefit plans: 4 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 false false No definition available. false 20 Prior service cost arising during period, net of taxes of $1.0 and $4.9 during 2009 and 2008, respectively 5 us-gaap_OtherComprehensiveIncomeDefinedBenefitPlanNetPriorServiceCostsCreditArisingDuringPeriodNetOfTax 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 -7200000 -7.2 true false 4 false false 0 0 true false 5 false true -7200000 -7.2 false false No definition available. No authoritative reference available. false 21 Net (gain) loss arising during period, net of taxes of $(23.9), $229.2 and $(7.8) during 2009, 2008 and 2007, respectively 5 us-gaap_OtherComprehensiveIncomeDefinedBenefitPlansNetUnamortizedGainLossArisingDuringPeriodNetOfTax 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 -339900000 -339.9 true false 4 false false 0 0 true false 5 false true -339900000 -339.9 false false No definition available. No authoritative reference available. false 22 Amortization of net actuarial loss, prior service cost, and transition obligation included in net periodic benefit cost, net of taxes of $(19.8), $(14.9) and $(15.9) during 2009, 2008 and 2007, respectively 5 ceg_OtherComprehensiveIncomeAmortizationOfNetActuarialLossPriorServiceCostAndTransitionObligationRecognizedInNetPeriodicPensionCostNetOfTax ceg false credit duration monetary The adjustment to other comprehensive income for amortization of net actuarial loss, prior service cost and transition... 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 21300000 21.3 true false 4 false false 0 0 true false 5 false true 21300000 21.3 false false The adjustment to other comprehensive income for amortization of net actuarial loss, prior service cost and transition obligation recognized as a component of net periodic benefit cost during the period, after tax. No authoritative reference available. false 23 Deconsolidation of CENG joint venture: 4 ceg_DeconsolidationOfJointVentureAbstract ceg false 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 false false No definition available. false 26 Net unrealized (gains) losses on foreign currency translation, net of taxes of $(2.7), $0.1 and $(1.8) during 2009, 2008 and 2007, respectively 4 us-gaap_OtherComprehensiveIncomeForeignCurrencyTransactionAndTranslationAdjustmentNetOfTaxPeriodIncreaseDecrease 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 true -3100000 -3.1 true false 4 false false 0 0 true false 5 false true -3100000 -3.1 false false No definition available. No authoritative reference available. false 29 Other 3 ceg_OtherComprehensiveIncomeOtherAdjustmentsNetOfTax ceg false credit duration monetary This element represents other adjustments to accumulated comprehensive income during the period, after tax, not otherwise... 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 200000 0.2 true false 4 false false 0 0 true false 5 false true 200000 0.2 false false This element represents other adjustments to accumulated comprehensive income during the period, after tax, not otherwise specified in the taxonomy. No authoritative reference available. false 30 Total Comprehensive Income (Loss) 3 us-gaap_ComprehensiveIncomeNetOfTaxIncludingPortionAttributableToNoncontrollingInterest 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 -1314400000 -1314.4 true false 3 false true -1119200000 -1119.2 true false 4 false true -4000000 -4.0 true false 5 false true -2437600000 -2437.6 false false No definition available. No authoritative reference available. true 32 Effect of adoption of fair value measurement accounting standard 2 us-gaap_CumulativeEffectOfInitialAdoptionOfNewAccountingPrinciple 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 900000 0.9 true false 3 false false 0 0 true false 4 false false 0 0 true false 5 false true 900000 0.9 false false No definition available. No authoritative reference available. false 33 BGE preference stock dividends 2 us-gaap_DividendsPreferredStockCash 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 true -13200000 -13.2 true false 5 false true -13200000 -13.2 false false No definition available. No authoritative reference available. false 34 Common stock dividend declared ($0.96, $1.91 and $1.74 per share during 2009, 2008 and 2007, respectively) 2 us-gaap_DividendsCommonStockCash 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 -341300000 -341.3 true false 3 false false 0 0 true false 4 false false 0 0 true false 5 false true -341300000 -341.3 false false No definition available. No authoritative reference available. false 35 Common stock issued and share-based awards 2 ceg_StockIssuedDuringPeriodValueCommonStockIssuedAndShareBasedAwards ceg false credit duration monetary Value of new stock during the period and equity impact of any share-based compensation plan. false false false false false false false false false 1 false true 667300000 667.3 true false 2 false true -35800000 -35.8 true false 3 false false 0 0 true false 4 false false 0 0 true false 5 false true 631500000 631.5 false false Value of new stock during the period and equity impact of any share-based compensation plan. No authoritative reference available. false 36 Common stock issued and share-based awards (in shares) 3 ceg_StockIssuedDuringPeriodSharesCommonStockIssuedAndShareBasedAwards ceg false na duration shares Number of shares of new stock issued during the period and number of shares issued during the period as a result of any... false false false false false false false false false 1 false true 21406000 21406 [1] 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 false false Number of shares of new stock issued during the period and number of shares issued during the period as a result of any share-based compensation plan. No authoritative reference available. false 37 Common stock purchased 2 us-gaap_StockRepurchasedDuringPeriodValue us-gaap true debit duration monetary No definition available. false false false false false false false false false 1 false true -16100000 -16.1 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 -16100000 -16.1 false false No definition available. No authoritative reference available. false 38 Common stock purchased (in shares) 3 us-gaap_StockRepurchasedDuringPeriodShares us-gaap true na duration shares No definition available. false false false false false false false false false 1 false true -200000 -200 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 false false No definition available. No authoritative reference available. false 40 Common stock purchased and retired (in shares) 3 us-gaap_StockRepurchasedAndRetiredDuringPeriodShares us-gaap true na duration shares No definition available. false false false false false false false false false 1 false true -514000 -514 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 false false No definition available. No authoritative reference available. false 41 Other 2 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 true -200000 -0.2 true false 3 false false 0 0 true false 4 false false 0 0 true false 5 false true -200000 -0.2 false false No definition available. No authoritative reference available. false 42 Balance at Dec. 31, 2008 2 us-gaap_StockholdersEquityIncludingPortionAttributableToNoncontrollingInterest us-gaap true credit instant monetary No definition available. false false false true false false false true false 1 false true 3164500000 3164.5 true false 2 false true 2228700000 2228.7 true false 3 false true -2211800000 -2211.8 true false 4 false true 210100000 210.1 true false 5 false true 3391500000 3391.5 false false No definition available. No authoritative reference available. false 43 Balance (in shares) at Dec. 31, 2008 2 us-gaap_CommonStockSharesOutstanding us-gaap true na instant shares No definition available. false false false true false false false true false 1 false true 199129000 199129 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 false false No definition available. No authoritative reference available. false 6 Contribution from noncontrolling interest 2 ceg_NoncontrollingInterestIncrease ceg false credit duration monetary Increase in noncontrolling interest balance from contribution by noncontrolling interest. 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 true 8000000 8.0 true false 5 false true 8000000 8.0 false false Increase in noncontrolling interest balance from contribution by noncontrolling interest. No authoritative reference available. false 7 Other noncontrolling interest activity 2 us-gaap_MinorityInterestPeriodIncreaseDecrease 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 true 400000 0.4 true false 5 false true 400000 0.4 false false No definition available. No authoritative reference available. false 10 Comprehensive Income (Loss) 2 us-gaap_ComprehensiveIncomeNetOfTaxIncludingPortionAttributableToNoncontrollingInterestAbstract 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 false false No definition available. false 11 Net income (loss) 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 true 4443400000 4443.4 true false 3 false false 0 0 true false 4 false true 60000000 60.0 true false 5 false true 4503400000 4503.4 false false No definition available. No authoritative reference available. false 13 Hedging instruments: 4 us-gaap_OtherComprehensiveIncomeDerivativesQualifyingAsHedgesNetOfTaxPeriodIncreaseDecreaseAbstract 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 false false No definition available. false 14 Reclassification of net losses on hedging instruments from OCI to net income, net of taxes of $(898.5), $(120.2) and $(682.3) during 2009, 2008 and 2007, respectively 5 us-gaap_OtherComprehensiveIncomeReclassificationAdjustmentOnDerivativesIncludedInNetIncomeNetOfTax 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 1499400000 1499.4 true false 4 false false 0 0 true false 5 false true 1499400000 1499.4 false false No definition available. No authoritative reference available. false 15 Net unrealized loss on hedging instruments, net of taxes of $251.2, $561.6 and $408.2 during 2009, 2008 and 2007, respectively 5 us-gaap_OtherComprehensiveIncomeUnrealizedGainLossOnDerivativesArisingDuringPeriodNetOfTax 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 -474700000 -474.7 true false 4 false false 0 0 true false 5 false true -474700000 -474.7 false false No definition available. No authoritative reference available. false 16 Available-for-sale securities: 4 us-gaap_OtherComprehensiveIncomeAvailableForSaleSecuritiesAdjustmentNetOfTaxPeriodIncreaseDecreaseAbstract 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 false false No definition available. false 17 Reclassification of net gains (losses) on securities from OCI to net income, net of taxes of $(24.6), $(79.1) and $1.0 during 2009, 2008 and 2007, respectively 5 us-gaap_OtherComprehensiveIncomeReclassificationAdjustmentForSaleOfSecuritiesIncludedInNetIncomeNetOfTax 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 25400000 25.4 true false 4 false false 0 0 true false 5 false true 25400000 25.4 false false No definition available. No authoritative reference available. false 18 Net unrealized (gains) losses on securities, net of taxes of $(78.2), $189.8 and $(25.5) during 2009, 2008 and 2007, respectively 5 us-gaap_OtherComprehensiveIncomeUnrealizedHoldingGainLossOnSecuritiesArisingDuringPeriodNetOfTax 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 77700000 77.7 true false 4 false false 0 0 true false 5 false true 77700000 77.7 false false No definition available. No authoritative reference available. false 19 Defined benefit plans: 4 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 false false No definition available. false 20 Prior service cost arising during period, net of taxes of $1.0 and $4.9 during 2009 and 2008, respectively 5 us-gaap_OtherComprehensiveIncomeDefinedBenefitPlanNetPriorServiceCostsCreditArisingDuringPeriodNetOfTax 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 -1500000 -1.5 true false 4 false false 0 0 true false 5 false true -1500000 -1.5 false false No definition available. No authoritative reference available. false 21 Net (gain) loss arising during period, net of taxes of $(23.9), $229.2 and $(7.8) during 2009, 2008 and 2007, respectively 5 us-gaap_OtherComprehensiveIncomeDefinedBenefitPlansNetUnamortizedGainLossArisingDuringPeriodNetOfTax 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 26900000 26.9 true false 4 false false 0 0 true false 5 false true 26900000 26.9 false false No definition available. No authoritative reference available. false 22 Amortization of net actuarial loss, prior service cost, and transition obligation included in net periodic benefit cost, net of taxes of $(19.8), $(14.9) and $(15.9) during 2009, 2008 and 2007, respectively 5 ceg_OtherComprehensiveIncomeAmortizationOfNetActuarialLossPriorServiceCostAndTransitionObligationRecognizedInNetPeriodicPensionCostNetOfTax ceg false credit duration monetary The adjustment to other comprehensive income for amortization of net actuarial loss, prior service cost and transition... 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 30300000 30.3 true false 4 false false 0 0 true false 5 false true 30300000 30.3 false false The adjustment to other comprehensive income for amortization of net actuarial loss, prior service cost and transition obligation recognized as a component of net periodic benefit cost during the period, after tax. No authoritative reference available. false 23 Deconsolidation of CENG joint venture: 4 ceg_DeconsolidationOfJointVentureAbstract ceg false 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 false false No definition available. false 24 Net unrealized gains on nuclear decommissioning trust funds, net of taxes of $125.3 5 ceg_ReclassificationOfNetGainsOnNuclearDecommissioningTrustFundsFromOCIToNetIncome ceg false debit duration monetary This element represents the net unrealized gains/losses on nuclear decommissioning trust funds, net of taxes during the... 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 -125300000 -125.3 true false 4 false false 0 0 true false 5 false true -125300000 -125.3 false false This element represents the net unrealized gains/losses on nuclear decommissioning trust funds, net of taxes during the reporting period. No authoritative reference available. false 25 Net unrealized losses on defined benefit plans, net of taxes of $(94.6) 5 ceg_NetGainLossOnDefinedBenefitPlansArisingDuringPeriodNetOfTaxes ceg false credit duration monetary This element represents the net unrealized losses on defined benefit plans, net of taxes during the reporting period. 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 138000000 138.0 true false 4 false false 0 0 true false 5 false true 138000000 138.0 false false This element represents the net unrealized losses on defined benefit plans, net of taxes during the reporting period. No authoritative reference available. false 26 Net unrealized (gains) losses on foreign currency translation, net of taxes of $(2.7), $0.1 and $(1.8) during 2009, 2008 and 2007, respectively 4 us-gaap_OtherComprehensiveIncomeForeignCurrencyTransactionAndTranslationAdjustmentNetOfTaxPeriodIncreaseDecrease 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 true 7100000 7.1 true false 4 false false 0 0 true false 5 false true 7100000 7.1 false false No definition available. No authoritative reference available. false 27 Other comprehensive income - equity investment in CENG, net of taxes of $(11.7) 3 ceg_OtherComprehensiveIncomeEquityInvestmentInCENGJointVentureNetOfTaxes ceg false credit duration monetary This element represents other comprehensive income related to equity investment in CENG joint venture during the period,... 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 12900000 12.9 true false 4 false false 0 0 true false 5 false true 12900000 12.9 false false This element represents other comprehensive income related to equity investment in CENG joint venture during the period, after tax. No authoritative reference available. false 28 Other comprehensive income related to other equity method investees, net of taxes of $(1.3) 3 ceg_OtherComprehensiveIncomeEquityInvestmentOtherNetOfTax ceg false credit duration monetary This element represents other comprehensive income related to other equity investments during the period, 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 2100000 2.1 true false 4 false false 0 0 true false 5 false true 2100000 2.1 false false This element represents other comprehensive income related to other equity investments during the period, net of tax. No authoritative reference available. false 30 Total Comprehensive Income (Loss) 3 us-gaap_ComprehensiveIncomeNetOfTaxIncludingPortionAttributableToNoncontrollingInterest 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 4443400000 4443.4 true false 3 false true 1218300000 1218.3 true false 4 false true 60000000 60.0 true false 5 false true 5721700000 5721.7 false false No definition available. No authoritative reference available. true 33 BGE preference stock dividends 2 us-gaap_DividendsPreferredStockCash 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 true -13200000 -13.2 true false 5 false true -13200000 -13.2 false false No definition available. No authoritative reference available. false 34 Common stock dividend declared ($0.96, $1.91 and $1.74 per share during 2009, 2008 and 2007, respectively) 2 us-gaap_DividendsCommonStockCash 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 -192200000 -192.2 true false 3 false false 0 0 true false 4 false false 0 0 true false 5 false true -192200000 -192.2 false false No definition available. No authoritative reference available. false 35 Common stock issued and share-based awards 2 ceg_StockIssuedDuringPeriodValueCommonStockIssuedAndShareBasedAwards ceg false credit duration monetary Value of new stock during the period and equity impact of any share-based compensation plan. false false false false false false false false false 1 false true 65100000 65.1 true false 2 false true -18900000 -18.9 true false 3 false false 0 0 true false 4 false false 0 0 true false 5 false true 46200000 46.2 false false Value of new stock during the period and equity impact of any share-based compensation plan. No authoritative reference available. false 36 Common stock issued and share-based awards (in shares) 3 ceg_StockIssuedDuringPeriodSharesCommonStockIssuedAndShareBasedAwards ceg false na duration shares Number of shares of new stock issued during the period and number of shares issued during the period as a result of any... false false false false false false false false false 1 false true 1856000 1856 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 false false Number of shares of new stock issued during the period and number of shares issued during the period as a result of any share-based compensation plan. No authoritative reference available. false 42 Balance at Dec. 31, 2009 2 us-gaap_StockholdersEquityIncludingPortionAttributableToNoncontrollingInterest us-gaap true credit instant monetary No definition available. false false false true false false false true false 1 true true 3229600000 3229.6 true false 2 true true 6461000000 6461.0 true false 3 true true -993500000 -993.5 true false 4 true true 265300000 265.3 true false 5 true true 8962400000 8962.4 false false No definition available. No authoritative reference available. false 43 Balance (in shares) at Dec. 31, 2009 2 us-gaap_CommonStockSharesOutstanding us-gaap true na instant shares No definition available. false false false true false false false true false 1 false true 200985000 200985 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 false false No definition available. No authoritative reference available. false 1 Includes 19,897.3 million shares issued to Mid American Energy Holdings Company. false 5 85 false HundredThousands Thousands UnKnown false true