Related Party Transactions - Additional Information (Detail) (USD $) In Millions, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2013	Sep. 30, 2012
Potomac Electric Power Co [Member] | PHI Service Company [Member]
Costs directly charged or allocated	$ 50	$ 55	$ 157	$ 158
Potomac Electric Power Co [Member] | Pepco Energy Services [Member]
Maintenance services	4	4	16	14
Delmarva Power & Light Co/De [Member] | PHI Service Company [Member]
Costs directly charged or allocated	38	40	115	114
Atlantic City Electric Co [Member] | PHI Service Company [Member]
Costs directly charged or allocated	$ 28	$ 31	$ 87	$ 86