Discontinued Operations - Operating Results for Retail Electric and Natural Gas Supply Businesses (Parenthetical) (Detail) (USD $) In Millions, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2014	Sep. 30, 2013	Sep. 30, 2014	Sep. 30, 2013
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Income tax expense, income from operations of discontinued operations	$ 0	$ 0	$ 0	$ (44)
Income tax expense (benefit) from discontinued operations	0	4	0	(1)
Discontinued Operations [Member] | Pepco Energy Services [Member]
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Income tax expense, income from operations of discontinued operations	0	1	0	3
Income tax expense (benefit) from discontinued operations	$ 0	$ 0	$ 0	$ 0