Derivative Instruments And Hedging Activities (Narrative) (Details) (USD $) In Millions, unless otherwise specified					3 Months Ended
	Mar. 31, 2012	Dec. 31, 2011	Mar. 31, 2012 Pepco Energy Services [Member]	Dec. 31, 2011 Pepco Energy Services [Member]	Mar. 31, 2012 Natural Gas Derivatives [Member] Pepco Energy Services [Member]
Trading Activity, Gains and Losses, Net [Line Items]
Credit risk derivative liabilities, at fair value	$ 40	$ 54
Derivative losses included in AOCL					33
Net settlement amount in the event of a downgrade below investment grade	111	124
Additional collateral that would have to be posted in the event of an investment downgrade	111	123
Cash plus borrowing capacity to meet future liquidity needs	679	1,000
Debt instrument unused borrowing capacity amount for subsidiary			227	283
Cash collateral posted	0	1
Credit risk derivative liabilities, at fair value net	$ 40	$ 53