Related Party Transactions - Additional Information (Detail) (USD $) In Millions, unless otherwise specified	3 Months Ended
	Mar. 31, 2014	Mar. 31, 2013
Potomac Electric Power Co [Member] | Pepco Energy Services [Member]
Related Party Transaction [Line Items]
Maintenance services	$ 5	$ 8
Potomac Electric Power Co [Member] | PHI Service Company [Member]
Related Party Transaction [Line Items]
Costs directly charged or allocated	53	55
Delmarva Power & Light Co/De [Member] | PHI Service Company [Member]
Related Party Transaction [Line Items]
Costs directly charged or allocated	39	40
Atlantic City Electric Co [Member] | PHI Service Company [Member]
Related Party Transaction [Line Items]
Costs directly charged or allocated	$ 29	$ 31