Derivative Instruments And Hedging Activities (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	Dec. 31, 2011
Credit risk derivative liabilities, at fair value	$ 20		$ 20		$ 54
Credit risk derivative liabilities, at fair value net	20		20		53
Cash collateral posted					1
Net settlement amount in the event of a downgrade below investment grade	72		72		124
Additional collateral that would have to be posted in the event of an investment downgrade	72		72		123
Cash plus borrowing capacity to meet future liquidity needs	969		969		994
Derivative assets (non-current assets)	8		8
Derivative liabilities (non-current liabilities)	10		10		6
Pepco Energy Services [Member]
Debt instrument unused borrowing capacity amount for subsidiary	383		383		283
Unrealized loss on derivatives	5	(5)	(5)	(5)
Pepco Energy Services [Member] | Natural Gas Derivatives [Member]
Derivative losses included in AOCL			25
Delmarva Power & Light Co/De [Member]
Credit risk derivative liabilities, at fair value	10		10		15
Credit risk derivative liabilities, at fair value net	10		10		15
Net settlement amount in the event of a downgrade below investment grade	9		9		15
Additional collateral that would have to be posted in the event of an investment downgrade	9		9		15
Cash plus borrowing capacity to meet future liquidity needs	586		586		711
Derivative liabilities (non-current liabilities)					3
Atlantic City Electric Co [Member]
Derivative assets (non-current assets)	8		8
Derivative liabilities (non-current liabilities)	9		9
Unrealized loss on derivatives	$ 1		$ 1