Derivative Instruments And Hedging Activities (Net Outstanding Natural Gas Commodity Forward Contracts That Did Not Qualify For Hedge Accounting) (Details)	12 Months Ended
	Dec. 31, 2011	Dec. 31, 2010
Financial Transmission Rights (MWh) [Member] | Pepco Energy Services [Member]
Derivative [Line Items]
Net Position	Long	Long
Commodity forward contracts	267,480	381,215
Natural Gas (MMBtu) [Member] | Pepco Energy Services [Member]
Derivative [Line Items]
Net Position	Long	Long
Commodity forward contracts	24,550,257	45,889,486
Natural Gas (MMBtu) [Member] | Delmarva Power & Light Co/De [Member]
Derivative [Line Items]
Net Position	Long	Long
Commodity forward contracts	6,161,200	8,236,500
Electricity (Mwh) [Member] | Pepco Energy Services [Member]
Derivative [Line Items]
Net Position	Long	Long
Commodity forward contracts	788,280	1,455,800
Electric Capacity (MW-Days) [Member] | Pepco Energy Services [Member]
Derivative [Line Items]
Net Position	Long	Long
Commodity forward contracts	12,920	2,265