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Impairment of Long-Lived Assets (Details) (USD $)
In Millions, unless otherwise specified
 3 Months Ended
Mar. 31, 2015
Mar. 31, 2014
Capital Leases, Net Investment in Direct Financing Leases [Abstract]    
Proceeds From Lease Termination $ 0exc_ProceedsFromLeaseTermination $ 335exc_ProceedsFromLeaseTermination
Operating and maintenance 2,081us-gaap_OtherCostAndExpenseOperating 1,858us-gaap_OtherCostAndExpenseOperating
Exelon Generation Co L L C [Member]    
Capital Leases, Net Investment in Direct Financing Leases [Abstract]    
Operating and maintenance $ 1,162us-gaap_OtherCostAndExpenseOperating
/ dei_LegalEntityAxis
= exc_ExelonGenerationCoLLCMember		 $ 938us-gaap_OtherCostAndExpenseOperating
/ dei_LegalEntityAxis
= exc_ExelonGenerationCoLLCMember