Related Party Transactions - Additional Information (Detail) (USD $) In Millions, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2013	Jun. 30, 2012	Jun. 30, 2013	Jun. 30, 2012
Potomac Electric Power Co [Member] | PHI Service Company [Member]
Costs directly charged or allocated	$ 52	$ 52	$ 107	$ 103
Potomac Electric Power Co [Member] | Pepco Energy Services [Member]
Maintenance services	4	6	12	10
Delmarva Power & Light Co/De [Member] | PHI Service Company [Member]
Costs directly charged or allocated	38	37	78	74
Atlantic City Electric Co [Member] | PHI Service Company [Member]
Costs directly charged or allocated	$ 28	$ 28	$ 59	$ 56