Related Party Transactions (Narrative) (Detail) (USD $) In Millions, unless otherwise specified	3 Months Ended
	Mar. 31, 2013	Mar. 31, 2012
Potomac Electric Power Co [Member] | PHI Service Company [Member]
Costs directly charged or allocated	$ 55	$ 51
Potomac Electric Power Co [Member] | Pepco Energy Services [Member]
Maintenance services	8	5
Delmarva Power & Light Co/De [Member] | PHI Service Company [Member]
Costs directly charged or allocated	40	37
Atlantic City Electric Co [Member] | PHI Service Company [Member]
Costs directly charged or allocated	$ 31	$ 28