Related Party Transactions - Schedule of Related Party Transactions Included in Balance Sheet (Detail) (USD $) In Millions, unless otherwise specified	Mar. 31, 2015	Dec. 31, 2014
Potomac Electric Power Co [Member]
Related Party Transaction [Line Items]
Payable to Related Party, Total	$ (51)	$ (30)
Potomac Electric Power Co [Member] | PHI Service Company [Member]
Related Party Transaction [Line Items]
Payable to Related Party, Total	(34)	(27)
Potomac Electric Power Co [Member] | Pepco Energy Services [Member]
Related Party Transaction [Line Items]
Payable to Related Party, Total	(4)	(2)
Potomac Electric Power Co [Member] | Other [Member]
Related Party Transaction [Line Items]
Payable to Related Party, Total	(13)	(1)
Delmarva Power & Light Co/De [Member]
Related Party Transaction [Line Items]
Payable to Related Party, Total	(21)	(17)
Delmarva Power & Light Co/De [Member] | PHI Service Company [Member]
Related Party Transaction [Line Items]
Payable to Related Party, Total	(21)	(18)
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	(17)	(15)
Atlantic City Electric Co [Member] | PHI Service Company [Member]
Related Party Transaction [Line Items]
Payable to Related Party, Total	(15)	(14)
Atlantic City Electric Co [Member] | Other [Member]
Related Party Transaction [Line Items]
Payable to Related Party, Total	$ (2)	$ (1)