Related Party Transactions (Narrative) (Detail) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Potomac Electric Power Co [Member]
Capital contribution from Parent	$ 50
Potomac Electric Power Co [Member] | PHI Service Company [Member]
Costs directly charged or allocated	211	185	186
Potomac Electric Power Co [Member] | Pepco Energy Services [Member]
Maintenance services	16	20	10
Delmarva Power & Light Co/De [Member]
Capital contribution from Parent	60		11
Delmarva Power & Light Co/De [Member] | PHI Service Company [Member]
Costs directly charged or allocated	153	133	139
Atlantic City Electric Co [Member]
Capital contribution from Parent		60	43
Atlantic City Electric Co [Member] | PHI Service Company [Member]
Costs directly charged or allocated	$ 117	$ 102	$ 100