2.2.0.7 true Pension, Postretirement, Other Postemployment, and Employee Savings Plan Benefits (Details 6) (USD $) 4075 - Disclosure - Pension, Postretirement, Other Postemployment, and Employee Savings Plan Benefits (Details 6) true false In Millions false false 1 USD true false false false ceg_QualifiedPensionPlansMember us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis xbrldi http://xbrl.org/2006/xbrldi ceg_QualifiedPensionPlansMember us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis explicitMember false false us-gaap_FairValueInputsLevel3Member us-gaap_DefinedBenefitPlanFairValueOfPlanAssetsByMeasurementAxis xbrldi http://xbrl.org/2006/xbrldi us-gaap_FairValueInputsLevel3Member us-gaap_DefinedBenefitPlanFairValueOfPlanAssetsByMeasurementAxis explicitMember USD Standard http://www.xbrl.org/2003/iso4217 USD iso4217 0 $ 5 Change in plan assets 3 us-gaap_DefinedBenefitPlanChangeInFairValueOfPlanAssetsRollForward us-gaap true na duration No definition available. false false false false false true false false false false false false 1 false false false false 0 0 true false false xbrli:stringItemType string A roll forward is a reconciliation of a concept from the beginning of a period to the end of a period. false 6 Fair value of plan assets at beginning of period 4 us-gaap_DefinedBenefitPlanFairValueOfPlanAssets us-gaap true debit instant No definition available. false false false false false false false false true false false periodstartlabel false 1 true true false false 96300000 96.3 true false false xbrli:monetaryItemType monetary Assets, usually stocks, bonds, and other investments, that have been segregated and restricted (usually in a trust) to provide benefits, at their fair value as of the measurement date. Plan assets include amounts contributed by the employer (and by employees for a contributory plan) and amounts earned from investing the contributions, less benefits paid. If a plan has liabilities other than for benefits, those nonbenefit obligations may be considered as reductions of plan assets. Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Statement of Financial Accounting Standard (FAS) -Number 132R -Paragraph 5 -Subparagraph b Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Statement of Financial Accounting Standard (FAS) -Number 132R -Paragraph 5 -Subparagraph d(iv)(b)(i) Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Statement of Financial Accounting Standard (FAS) -Number 87 -Paragraph 49 false 7 Actual return on plan assets: 4 us-gaap_DefinedBenefitPlanActualReturnOnPlanAssetsAbstract us-gaap true na duration No definition available. false false false false false true false false false false false false 1 false false false false 0 0 true false false xbrli:stringItemType string dup_1_The difference between fair value of plan assets at the end of the period and the fair value at the beginning of the period, adjusted for contributions and payments of benefits during the period, and after adjusting for taxes and other expenses, as applicable. 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Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Statement of Financial Accounting Standard (FAS) -Number 132R -Paragraph 5 -Subparagraph d(iv)(b)(i) false 10 Purchases, sales, and settlements 4 us-gaap_DefinedBenefitPlanPurchasesSalesAndSettlements us-gaap true debit duration No definition available. false false false false false false false false false false false terselabel false 1 false true false false -10800000 -10.8 true false false xbrli:monetaryItemType monetary Purchases, sales, and settlements of plan assets that occurred during the period. Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Statement of Financial Accounting Standard (FAS) -Number 132R -Paragraph 5 -Subparagraph d(iv)(b)(ii) false 11 Transfers into and out of Level 3 4 us-gaap_DefinedBenefitPlanTransfersBetweenMeasurementLevels us-gaap true debit duration No definition available. false false false false false false false false false false false terselabel false 1 false true false false -15000000 -15.0 true false false xbrli:monetaryItemType monetary Transfers in and out of Level 3. For example, transfers due to changes in the observability of significant inputs. 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