Significant Accounting Policies (Annual Depreciation Rates) (Details)	12 Months Ended
	Dec. 31, 2011		Dec. 31, 2010		Dec. 31, 2009
Electric Transmission and Distribution [Member] | Atlantic City Electric Co [Member]
Significant Accounting Policies [Line Items]
Annual Depreciation Rate	3.00%		2.80%		2.80%
Electric Transmission and Distribution [Member] | Delmarva Power & Light Co/De [Member]
Significant Accounting Policies [Line Items]
Annual Depreciation Rate	2.80%		2.80%		2.80%
Electric Transmission and Distribution [Member] | Potomac Electric Power Co [Member]
Significant Accounting Policies [Line Items]
Annual Depreciation Rate	2.60%		2.60%		2.70%
Generation [Member] | Pepco Energy Services [Member]
Significant Accounting Policies [Line Items]
Annual Depreciation Rate	10.20%	[1]	16.90%	[1]	11.40%	[1]

[1] Percentages reflect accelerated depreciation of the Benning Road and Buzzard Point generating plants scheduled for retirement in May 2012.