Income Taxes (Reconciliation Of Beginning And Ending Balances Of Unrecognized Tax Benefits) (Detail) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Unrecognized Tax Benefits [Line Items]
Unrecognized Tax Benefits, Beginning balance	$ 357	$ 395	$ 246
Tax positions related to current year, additions	1	2	150
Tax positions related to prior years, additions	79	20	35
Tax positions related to prior years, reductions	(235)	(57)	(36)
Settlements	(2)	(3)
Unrecognized Tax Benefits, Ending balance	200	357	395
Potomac Electric Power Co [Member]
Unrecognized Tax Benefits [Line Items]
Unrecognized Tax Benefits, Beginning balance	173	190	71
Tax positions related to current year, additions			110
Tax positions related to prior years, additions	60	12	24
Tax positions related to prior years, reductions	(142)	(26)	(15)
Settlements		(3)
Unrecognized Tax Benefits, Ending balance	91	173	190
Delmarva Power & Light Co/De [Member]
Unrecognized Tax Benefits [Line Items]
Unrecognized Tax Benefits, Beginning balance	35	40	39
Tax positions related to current year, additions			3
Tax positions related to prior years, additions		7	5
Tax positions related to prior years, reductions	(26)	(12)	(7)
Unrecognized Tax Benefits, Ending balance	9	35	40
Atlantic City Electric Co [Member]
Unrecognized Tax Benefits [Line Items]
Unrecognized Tax Benefits, Beginning balance	79	83	39
Tax positions related to current year, additions	1	2	50
Tax positions related to current year, reductions			(1)
Tax positions related to prior years, additions	8	4
Tax positions related to prior years, reductions	(69)	(10)	(5)
Settlements	(2)
Unrecognized Tax Benefits, Ending balance	$ 17	$ 79	$ 83