Related Party Transactions (Narrative) (Detail) (USD $) In Millions, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2012	Jun. 30, 2011	Jun. 30, 2012	Jun. 30, 2011
Potomac Electric Power Co [Member] | Phi Service Company [Member]
Costs directly charged or allocated	$ 52	$ 43	$ 103	$ 86
Potomac Electric Power Co [Member] | Pepco Energy Services [Member]
Maintenance services	6	4	10	8
Delmarva Power & Light Co/De [Member] | Phi Service Company [Member]
Costs directly charged or allocated	37	31	74	62
Atlantic City Electric Co [Member] | Phi Service Company [Member]
Costs directly charged or allocated	$ 28	$ 24	$ 56	$ 48