Significant Accounting Policies (Annual Depreciation Rates) (Detail)	12 Months Ended
	Dec. 31, 2012		Dec. 31, 2011		Dec. 31, 2010
Electric Transmission and Distribution [Member] | Potomac Electric Power Co [Member]
Interest Cost Capitalized And Depreciation And Amortization Expenses For Property, Plant and Equipment [Line Items]
Annual Depreciation Rate	2.50%		2.60%		2.60%
Electric Transmission and Distribution [Member] | Delmarva Power & Light Co/De [Member]
Interest Cost Capitalized And Depreciation And Amortization Expenses For Property, Plant and Equipment [Line Items]
Annual Depreciation Rate	2.70%		2.80%		2.80%
Electric Transmission and Distribution [Member] | Atlantic City Electric Co [Member]
Interest Cost Capitalized And Depreciation And Amortization Expenses For Property, Plant and Equipment [Line Items]
Annual Depreciation Rate	3.00%		3.00%		2.80%
Electric Transmission and Distribution [Member] | Pepco Energy Services [Member]
Interest Cost Capitalized And Depreciation And Amortization Expenses For Property, Plant and Equipment [Line Items]
Annual Depreciation Rate		[1]		[1]		[1]
Generation [Member] | Pepco Energy Services [Member]
Interest Cost Capitalized And Depreciation And Amortization Expenses For Property, Plant and Equipment [Line Items]
Annual Depreciation Rate	6.40%	[1]	10.20%	[1]	16.90%	[1]

[1] Percentages reflect accelerated depreciation of the Benning Road and Buzzard Point generating facilities retired during 2012.