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No authoritative reference available. false 74 Intangible Assets Subject to Amortization 2 us-gaap_FiniteLivedIntangibleAssetsLineItems 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 false false false 2 false false false false 0 0 false false false 3 false false false false 0 0 false false false xbrli:stringItemType string Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table. false 75 Gross Carrying Amount 2 us-gaap_FiniteLivedIntangibleAssetsGross us-gaap true debit instant No definition available. false false false false false false false false false false false terselabel false 1 false true false false 29000000 29.0 false false false 2 false true false false 43900000 43.9 false false false 3 false false false false 0 0 false false false xbrli:monetaryItemType monetary Sum of the gross carrying amounts before accumulated amortization as of the balance sheet date of all intangible assets having statutory or estimated useful lives. The aggregate gross carrying amount (including any previously recognized impairment charges) of a major finite-lived intangible asset class. A major class is composed of intangible assets that can be grouped together because they are similar, either by their nature or by their use in the operations of a company. Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Statement of Financial Accounting Standard (FAS) -Number 142 -Paragraph 45 -Subparagraph a(1) false 76 Accumulated Amortization 2 us-gaap_FiniteLivedIntangibleAssetsAccumulatedAmortization us-gaap true credit instant No definition available. false false false false false false false false false false true negated false 1 false true false false -13900000 -13.9 false false false 2 false true false false -22600000 -22.6 false false false 3 false false false false 0 0 false false false xbrli:monetaryItemType monetary The accumulated amount of amortization of a major finite-lived intangible asset class. A major class is composed of intangible assets that can be grouped together because they are similar, either by their nature or by their use in the operations of a company. Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Statement of Financial Accounting Standard (FAS) -Number 142 -Paragraph 45 -Subparagraph a(1) false 77 Net Asset 2 us-gaap_FiniteLivedIntangibleAssetsNet us-gaap true debit instant No definition available. false false false false false false false false false false false totallabel false 1 false true false false 15100000 15.1 false false false 2 false true false false 21300000 21.3 false false false 3 false false false false 0 0 false false false xbrli:monetaryItemType monetary The aggregate sum of gross carrying value of a major finite-lived intangible asset class, less accumulated amortization and any impairment charges. A major class is composed of intangible assets that can be grouped together because they are similar, either by their nature or by their use in the operations of a company. Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Statement of Financial Accounting Standard (FAS) -Number 142 -Paragraph 45 -Subparagraph a(1) true 85 Nonregulated businesses 0 na true na na No definition available. false true false false false false false false false false false http://www.constellation.com/role/disclosureintangibleassetsdetails2 false 1 false false false false 0 0 false false false 2 false false false false 0 0 false false false 3 false false false false 0 0 false false false false 16 USD true false false false Nonregulated businesses dei_LegalEntityAxis xbrldi http://xbrl.org/2006/xbrldi ceg_NonRegulatedBusinessMember dei_LegalEntityAxis explicitMember USD Standard http://www.xbrl.org/2003/iso4217 USD iso4217 0 $ false 17 USD true false false false Nonregulated businesses dei_LegalEntityAxis xbrldi http://xbrl.org/2006/xbrldi ceg_NonRegulatedBusinessMember dei_LegalEntityAxis explicitMember USD Standard http://www.xbrl.org/2003/iso4217 USD iso4217 0 $ false 18 USD true false false false Nonregulated businesses dei_LegalEntityAxis xbrldi http://xbrl.org/2006/xbrldi ceg_NonRegulatedBusinessMember dei_LegalEntityAxis explicitMember USD Standard http://www.xbrl.org/2003/iso4217 USD iso4217 0 $ na No definition available. 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If an intangible asset has a finite useful life, but the precise length of that life is not known, that intangible asset shall be amortized over the best estimate of its useful life. 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Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Statement of Financial Accounting Standard (FAS) -Number 142 -Paragraph 45 -Subparagraph a(3) false 93 2011 2 us-gaap_FutureAmortizationExpenseYearTwo 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 45100000 45.1 false false false 2 false false false false 0 0 false false false 3 false false false false 0 0 false false false xbrli:monetaryItemType monetary The amount of amortization expense expected to be recognized during the second twelve-month period following the balance sheet date. 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