Commitments And Contingencies (Tax Legislation, Guarantees, Indemnifications, And Performance Contracts) (Detail) (USD $) In Millions, except Per Share data, unless otherwise specified	1 Months Ended
	Mar. 31, 2013
Commitment And Contingencies [Line Items]
Value of guarantees on both completed projects and projects under construction	$ 441
Value of guarantees under construction projects	15
Dividend declared on common stock, per share	$ 0.27
Energy Savings Or Combined Heat And Power Performance [Member]
Commitment And Contingencies [Line Items]
Accrued liability on contracts	$ 1
Pepco Energy Services [Member] | Energy Savings Or Combined Heat And Power Performance [Member]
Commitment And Contingencies [Line Items]
Contract life, maximum remaining term	20
Pepco Energy Services [Member] | Performance Contracts Associated With Savings Guarantees [Member]
Commitment And Contingencies [Line Items]
Contract life, maximum remaining term	13