Derivative Instruments And Hedging Activities (Narrative) (Details) (USD $)	12 Months Ended				12 Months Ended
	Dec. 31, 2010	Dec. 31, 2011	Dec. 31, 2011 Pepco Energy Services [Member]	Dec. 31, 2010 Pepco Energy Services [Member]	Dec. 31, 2011 Natural Gas Derivatives [Member]
Credit risk derivative liabilities, at fair value	$ 156,000,000	$ 54,000,000
Derivative Gain Loss On Derivative, Net	9,000,000				42,000,000
Derivative, Loss on Derivative	15,000,000
Net settlement amount in the event of a downgrade below investment grade	182,000,000	124,000,000
Cash plus borrowing capacity to meet future liquidity needs			1,000,000,000	1,200,000,000
Debt instrument unused borrowing capacity amount for subsidiary			283,000,000	728,000,000
Cash collateral posted		1,000,000
Credit risk derivative liabilities, at fair value net		$ 53,000,000