Derivative Instruments And Hedging Activities (Outstanding Energy Commodity Contracts Employed As Cash Flow Hedges) (Detail) (Pepco Energy Services [Member], Electricity (Megawatt Hours (MWh)) [Member])	Jun. 30, 2012 mwh	Dec. 31, 2011 mwh
Forecasted Purchases Hedges [Member]
Derivative [Line Items]
Derivative, Nonmonetary Notional Amount	3,360	614,560
Forecasted Sales Hedges [Member]
Derivative [Line Items]
Derivative, Nonmonetary Notional Amount	3,360	614,560