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Consolidated Statement of Changes in Shareholders Equity (Unaudited) (Parenthetical) (USD $)
In Millions, unless otherwise specified
 3 Months Ended
Mar. 31, 2015
Mar. 31, 2014
Income taxes $ 363us-gaap_IncomeTaxExpenseBenefit $ (54)us-gaap_IncomeTaxExpenseBenefit
Exelon Generation Co L L C [Member]    
Income taxes 226us-gaap_IncomeTaxExpenseBenefit
/ dei_LegalEntityAxis
= exc_ExelonGenerationCoLLCMember		 (199)us-gaap_IncomeTaxExpenseBenefit
/ dei_LegalEntityAxis
= exc_ExelonGenerationCoLLCMember
PECO Energy Co [Member]    
Income taxes 58us-gaap_IncomeTaxExpenseBenefit
/ dei_LegalEntityAxis
= exc_PecoEnergyCoMember		 34us-gaap_IncomeTaxExpenseBenefit
/ dei_LegalEntityAxis
= exc_PecoEnergyCoMember
Commonwealth Edison Co [Member]    
Income taxes 59us-gaap_IncomeTaxExpenseBenefit
/ dei_LegalEntityAxis
= exc_CommonwealthEdisonCoMember		 65us-gaap_IncomeTaxExpenseBenefit
/ dei_LegalEntityAxis
= exc_CommonwealthEdisonCoMember
Baltimore Gas and Electric Company [Member]    
Income taxes $ 74us-gaap_IncomeTaxExpenseBenefit
/ dei_LegalEntityAxis
= exc_BaltimoreGasAndElectricCompanyMember		 $ 58us-gaap_IncomeTaxExpenseBenefit
/ dei_LegalEntityAxis
= exc_BaltimoreGasAndElectricCompanyMember