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Segment Information - Narrative (Details) (USD $)
In Millions, unless otherwise specified
 3 Months Ended
Mar. 31, 2015
Mar. 31, 2014
Segment Reporting Information [Line Items]    
Number of reportable segments 9us-gaap_NumberOfReportableSegments  
Other Segments [Member]    
Segment Reporting Information [Line Items]    
Segment Reporting Information Revenue Net of Purchase Power And Fuel $ 1,929exc_SegmentReportingInformationRevenueNetOfPurchasePowerAndFuel
/ us-gaap_StatementBusinessSegmentsAxis
= us-gaap_AllOtherSegmentsMember		 $ 1,554exc_SegmentReportingInformationRevenueNetOfPurchasePowerAndFuel
/ us-gaap_StatementBusinessSegmentsAxis
= us-gaap_AllOtherSegmentsMember
Exelon Generation Co L L C [Member]    
Segment Reporting Information [Line Items]    
Number of reportable segments 6us-gaap_NumberOfReportableSegments
/ us-gaap_StatementBusinessSegmentsAxis
= exc_ExelonGenerationCoLLCMember		  
Operating Segments [Member] | Exelon Generation Co L L C [Member]    
Segment Reporting Information [Line Items]    
Utility Taxes 27exc_UtilityTaxes
/ us-gaap_ConsolidationItemsAxis
= us-gaap_OperatingSegmentsMember
/ us-gaap_StatementBusinessSegmentsAxis
= exc_ExelonGenerationCoLLCMember		 24exc_UtilityTaxes
/ us-gaap_ConsolidationItemsAxis
= us-gaap_OperatingSegmentsMember
/ us-gaap_StatementBusinessSegmentsAxis
= exc_ExelonGenerationCoLLCMember
Operating Segments [Member] | Commonwealth Edison Co [Member]    
Segment Reporting Information [Line Items]    
Utility Taxes $ 62exc_UtilityTaxes
/ us-gaap_ConsolidationItemsAxis
= us-gaap_OperatingSegmentsMember
/ us-gaap_StatementBusinessSegmentsAxis
= exc_CommonwealthEdisonCoMember		 $ 63exc_UtilityTaxes
/ us-gaap_ConsolidationItemsAxis
= us-gaap_OperatingSegmentsMember
/ us-gaap_StatementBusinessSegmentsAxis
= exc_CommonwealthEdisonCoMember