Derivative Instruments And Hedging Activities (Net Outstanding Natural Gas Commodity Forward Contracts That Did Not Qualify For Hedge Accounting) (Detail)	6 Months Ended	12 Months Ended	6 Months Ended	12 Months Ended	6 Months Ended	12 Months Ended	6 Months Ended	12 Months Ended	6 Months Ended	12 Months Ended	6 Months Ended	12 Months Ended
	Jun. 30, 2012 Pepco Energy Services [Member] Financial Transmission Rights (MWh) [Member] mwh	Dec. 31, 2011 Pepco Energy Services [Member] Financial Transmission Rights (MWh) [Member] mwh	Jun. 30, 2012 Pepco Energy Services [Member] Electric Capacity (MW-Days) [Member]	Dec. 31, 2011 Pepco Energy Services [Member] Electric Capacity (MW-Days) [Member] MW	Jun. 30, 2012 Pepco Energy Services [Member] Electricity (Megawatt Hours (MWh)) [Member] mwh	Dec. 31, 2011 Pepco Energy Services [Member] Electricity (Megawatt Hours (MWh)) [Member] mwh	Jun. 30, 2012 Pepco Energy Services [Member] Natural Gas (One Million British Thermal Units (MMBtu)) [Member] MMBtu	Dec. 31, 2011 Pepco Energy Services [Member] Natural Gas (One Million British Thermal Units (MMBtu)) [Member] MMBtu	Jun. 30, 2012 Delmarva Power & Light Co/De [Member] Natural Gas (One Million British Thermal Units (MMBtu)) [Member] MMBtu	Jun. 30, 2011 Delmarva Power & Light Co/De [Member] Natural Gas (One Million British Thermal Units (MMBtu)) [Member] MMBtu	Jun. 30, 2012 Atlantic City Electric Co [Member] Capacity [Member] MW	Dec. 31, 2011 Atlantic City Electric Co [Member] Capacity [Member]
Derivative [Line Items]
Commodity forward contracts	366,472	267,480		12,920	528,856	788,280	9,474,741	24,550,257	2,966,600	6,161,200	180
Net Position	Long	Long	-	Long	Long	Long	Long	Long	Long	Long	Long	-