Derivative Instruments And Hedging Activities (Narrative) (Detail) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Estimated percentage of New Jersey load	15.00%
Derivative Gain Loss On Derivative, Net			$ 9
Derivative, Loss on Derivative			15
Credit risk derivative liabilities, at fair value	8	54
Cash collateral posted		1
Credit risk derivative liabilities, at fair value net	8	53
Net settlement amount in the event of a downgrade below investment grade	40	124
Additional collateral that would have to be posted in the event of an investment downgrade	40	123
Cash plus borrowing capacity to meet future liquidity needs	861	994
Derivative assets (non-current assets)	8
Derivative assets (non-current liabilities)	11	6
Pepco Energy Services [Member]
Derivative Gain Loss On Derivative, Net	24	(30)	(1)
Debt instrument unused borrowing capacity amount for subsidiary	384	283
Unrealized loss on derivatives	(3)	(30)	(3)
Pepco Energy Services [Member] | Natural Gas Derivatives [Member]
Derivative losses included in AOCL	11
Atlantic City Electric Co [Member]
Estimated percentage of New Jersey load	15.00%
Derivative assets (non-current assets)	8
Derivative assets (non-current liabilities)	11
Unrealized loss on derivatives	3
Delmarva Power & Light Co/De [Member]
Credit risk derivative liabilities, at fair value	4	15
Credit risk derivative liabilities, at fair value net	4	15
Net settlement amount in the event of a downgrade below investment grade	2	15
Additional collateral that would have to be posted in the event of an investment downgrade	2	15
Cash plus borrowing capacity to meet future liquidity needs	477	711
Derivative assets (non-current liabilities)		$ 3