Pension And Other Postretirement Benefits (Split Of The Combined Pension And Other Postretirement Net Periodic Benefit Costs) (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009
Defined Benefit Plan, Net Periodic Benefit Cost	$ 94	$ 116	$ 149
Potomac Electric Power Co [Member]
Defined Benefit Plan, Net Periodic Benefit Cost	43	40	38
Delmarva Power & Light Co/De [Member]
Defined Benefit Plan, Net Periodic Benefit Cost	23	28	25
Atlantic City Electric Co [Member]
Defined Benefit Plan, Net Periodic Benefit Cost	21	23	20
Subsidiaries [Member]
Defined Benefit Plan, Net Periodic Benefit Cost	$ 7	$ 25	$ 66