Discontinued Operations - Operating Results for Retail Electric and Natural Gas Supply Businesses (Parenthetical) (Detail) (USD $) In Millions, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2014	Jun. 30, 2013	Jun. 30, 2014	Jun. 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	$ 5	$ 0	$ (43)
Income tax expense (benefit) from discontinued operations	0	5	0	5
Pepco Energy Services [Member] | Discontinued Operations [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	0	0	1
Income tax expense (benefit) from discontinued operations	$ 0	$ 1	$ 0	$ 0