Derivative Instruments And Hedging Activities (Net Outstanding Commodity Forward Contracts Quantities And Net Position That Did Not Qualify For Hedge Accounting) (Detail) (Pepco Energy Services [Member])	12 Months Ended
	Dec. 31, 2012 ForwardContracts	Dec. 31, 2011 ForwardContracts
Financial Transmission Rights (MWh) [Member]
Derivative [Line Items]
Commodity forward contracts	181,008	267,480
Net Position	Long	Long
Electric Capacity (MW-Days) [Member]
Derivative [Line Items]
Commodity forward contracts		12,920
Net Position	-	Long
Electricity (Megawatt Hours (MWh)) [Member]
Derivative [Line Items]
Commodity forward contracts	261,240	788,280
Net Position	Long	Long
Natural Gas (One Million British Thermal Units (MMBtu)) [Member]
Derivative [Line Items]
Commodity forward contracts	2,867,500	24,550,257
Net Position	Long	Long