Derivative Instruments And Hedging Activities (Net Outstanding Natural Gas Commodity Forward Contracts That Did Not Qualify For Hedge Accounting) (Detail)	9 Months Ended	12 Months Ended
	Sep. 30, 2012 MWh	Dec. 31, 2011 MWh
Pepco Energy Services [Member] | Financial Transmission Rights (MWh) [Member]
Derivative [Line Items]
Commodity forward contracts	254,601	267,480
Net Position	Long	Long
Commodity forward contracts	254,601	267,480
Net Position	Long	Long
Pepco Energy Services [Member] | Electric Capacity (MW-Days) [Member]
Derivative [Line Items]
Commodity forward contracts		12,920
Net Position	-	Long
Commodity forward contracts		12,920
Net Position	-	Long
Pepco Energy Services [Member] | Electricity (Megawatt Hours (MWh)) [Member]
Derivative [Line Items]
Commodity forward contracts	261,240	788,280
Net Position	Long	Long
Commodity forward contracts	261,240	788,280
Net Position	Long	Long
Pepco Energy Services [Member] | Natural Gas (One Million British Thermal Units (MMBtu)) [Member]
Derivative [Line Items]
Commodity forward contracts	6,176,711	24,550,257
Net Position	Long	Long
Commodity forward contracts	6,176,711	24,550,257
Net Position	Long	Long
Delmarva Power & Light Co/De [Member] | Natural Gas (One Million British Thermal Units (MMBtu)) [Member]
Derivative [Line Items]
Commodity forward contracts	3,571,000	6,161,200
Net Position	Long	Long
Commodity forward contracts	3,571,000	6,161,200
Net Position	Long	Long
Atlantic City Electric Co [Member] | Capacity [Member]
Derivative [Line Items]
Commodity forward contracts	180
Net Position	Long	-
Commodity forward contracts	180
Net Position	Long	-