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Income Taxes - Summary of Interest Receivable (Payable) (Details) (USD $)
In Millions, unless otherwise specified
Dec. 31, 2014
Dec. 31, 2013
Income Taxes [Line Items]    
Net interest receivable (payable) recognized related to uncertain tax positions $ (310)exc_NetInterestReceivablePayableRelatedToUncertainTaxPositions $ (349)exc_NetInterestReceivablePayableRelatedToUncertainTaxPositions
Exelon Generation Co L L C [Member]    
Income Taxes [Line Items]    
Net interest receivable (payable) recognized related to uncertain tax positions 40exc_NetInterestReceivablePayableRelatedToUncertainTaxPositions
/ dei_LegalEntityAxis
= exc_ExelonGenerationCoLLCMember		 (37)exc_NetInterestReceivablePayableRelatedToUncertainTaxPositions
/ dei_LegalEntityAxis
= exc_ExelonGenerationCoLLCMember
Commonwealth Edison Co [Member]    
Income Taxes [Line Items]    
Net interest receivable (payable) recognized related to uncertain tax positions (203)exc_NetInterestReceivablePayableRelatedToUncertainTaxPositions
/ dei_LegalEntityAxis
= exc_CommonwealthEdisonCoMember		 (174)exc_NetInterestReceivablePayableRelatedToUncertainTaxPositions
/ dei_LegalEntityAxis
= exc_CommonwealthEdisonCoMember
PECO Energy Co [Member]    
Income Taxes [Line Items]    
Net interest receivable (payable) recognized related to uncertain tax positions 3exc_NetInterestReceivablePayableRelatedToUncertainTaxPositions
/ dei_LegalEntityAxis
= exc_PecoEnergyCoMember		 3exc_NetInterestReceivablePayableRelatedToUncertainTaxPositions
/ dei_LegalEntityAxis
= exc_PecoEnergyCoMember
Baltimore Gas and Electric Company [Member]    
Income Taxes [Line Items]    
Net interest receivable (payable) recognized related to uncertain tax positions $ (1)exc_NetInterestReceivablePayableRelatedToUncertainTaxPositions
/ dei_LegalEntityAxis
= exc_BaltimoreGasAndElectricCompanyMember		 $ 0exc_NetInterestReceivablePayableRelatedToUncertainTaxPositions
/ dei_LegalEntityAxis
= exc_BaltimoreGasAndElectricCompanyMember