Income Taxes - Reconciliation of Beginning and Ending Balances of Unrecognized Tax Benefits (Detail) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Unrecognized Tax Benefits [Line Items]
Unrecognized Tax Benefits, Beginning balance	$ 200	$ 357	$ 395
Tax positions related to current year, Additions	3	1	2
Tax positions related to current year, Reductions
Tax positions related to prior years, Additions	646	79	20
Tax positions related to prior years, Reductions	(12)	(235)	(57)
Settlements	(6)	(2)	(3)
Unrecognized Tax Benefits, Ending balance	831	200	357
Potomac Electric Power Co [Member]
Unrecognized Tax Benefits [Line Items]
Unrecognized Tax Benefits, Beginning balance	91	173	190
Tax positions related to current year, Additions	1
Tax positions related to current year, Reductions
Tax positions related to prior years, Additions	12	60	12
Tax positions related to prior years, Reductions	(3)	(142)	(26)
Settlements			(3)
Unrecognized Tax Benefits, Ending balance	101	91	173
Delmarva Power & Light Co/De [Member]
Unrecognized Tax Benefits [Line Items]
Unrecognized Tax Benefits, Beginning balance	9	35	40
Tax positions related to current year, Additions
Tax positions related to current year, Reductions
Tax positions related to prior years, Additions			7
Tax positions related to prior years, Reductions		(26)	(12)
Settlements
Unrecognized Tax Benefits, Ending balance	9	9	35
Atlantic City Electric Co [Member]
Unrecognized Tax Benefits [Line Items]
Unrecognized Tax Benefits, Beginning balance	17	79	83
Tax positions related to current year, Additions	2	1	2
Tax positions related to current year, Reductions
Tax positions related to prior years, Additions	1	8	4
Tax positions related to prior years, Reductions	(5)	(69)	(10)
Settlements	(6)	(2)
Unrecognized Tax Benefits, Ending balance	$ 9	$ 17	$ 79