Commitments and Contingencies - Tax Legislation, Guarantees, Indemnifications, And Performance Contracts - Additional Information (Detail) (USD $) In Millions, except Per Share data, unless otherwise specified	1 Months Ended			1 Months Ended
	Jun. 30, 2013	Jul. 25, 2013 Subsequent Event [Member]	Jun. 30, 2013 Energy Savings Or Combined Heat And Power Performance [Member] Maximum [Member]	Jun. 30, 2013 Pepco Energy Services [Member] Energy Savings Or Combined Heat And Power Performance [Member]	Jun. 30, 2013 Pepco Energy Services [Member] Performance Contracts Associated With Savings Guarantees [Member]
Commitment And Contingencies [Line Items]
Value of guarantees on both completed projects and projects under construction	$ 464
Contract life, maximum remaining term				20 years	13 years
Value of guarantees under construction projects	15
Accrued liability on contracts			$ 1
Dividend declared on common stock, per share		$ 0.27
Dividend declared, payable date		Sep. 30, 2013
Dividends payable, date of record		Sep. 10, 2013