Derivative Instruments and Hedging Activities - Net Outstanding Commodity Forward Contracts That Did Not Qualify For Hedge Accounting (Detail)	12 Months Ended
	Dec. 31, 2013 MMBTU	Dec. 31, 2012 MMBTU
Delmarva Power & Light Co/De [Member] | Natural Gas (One Million British Thermal Units (MMBtu)) [Member]
Derivative [Line Items]
Quantity	3,977,500	3,838,000
Net Position	Long	Long
Atlantic City Electric Co [Member] | Capacity (MWs) [Member]
Derivative [Line Items]
Quantity		180
Net Position		Long