Derivative Instruments And Hedging Activities (Outstanding Commodity Forward Contracts To Hedge Forecasted Transactions) (Details) (Delmarva Power & Light Co/De [Member], Forecasted Purchases Hedges [Member], Natural Gas (MMBtu) [Member])	Sep. 30, 2011	Dec. 31, 2010
Delmarva Power & Light Co/De [Member] | Forecasted Purchases Hedges [Member] | Natural Gas (MMBtu) [Member]
Derivative, Nonmonetary Notional Amount	942,500	1,670,000