Related Party Transactions - Schedule of Related Party Transactions Included in Balance Sheet (Detail) (USD $) In Millions, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013
Potomac Electric Power Co [Member]
Related Party Transaction [Line Items]
Payable to Related Party, Total	$ (30)	$ (32)
Potomac Electric Power Co [Member] | PHI Service Company [Member]
Related Party Transaction [Line Items]
Payable to Related Party, Total	(27)	(25)
Potomac Electric Power Co [Member] | Pepco Energy Services [Member]
Related Party Transaction [Line Items]
Payable to Related Party, Total	(2)	(7)
Potomac Electric Power Co [Member] | Other [Member]
Related Party Transaction [Line Items]
Payable to Related Party, Total	(1)
Delmarva Power & Light Co/De [Member]
Related Party Transaction [Line Items]
Payable to Related Party, Total	(17)	(22)
Delmarva Power & Light Co/De [Member] | PHI Service Company [Member]
Related Party Transaction [Line Items]
Payable to Related Party, Total	(18)	(22)
Delmarva Power & Light Co/De [Member] | Other [Member]
Related Party Transaction [Line Items]
Payable to Related Party, Total	1
Atlantic City Electric Co [Member]
Related Party Transaction [Line Items]
Payable to Related Party, Total	(15)	(15)
Atlantic City Electric Co [Member] | PHI Service Company [Member]
Related Party Transaction [Line Items]
Payable to Related Party, Total	(14)	(15)
Atlantic City Electric Co [Member] | Other [Member]
Related Party Transaction [Line Items]
Payable to Related Party, Total	$ (1)