Discontinued Operations - Operating Results for Retail Natural Gas Supply Business (Detail) (USD $) In Millions, unless otherwise specified	3 Months Ended	9 Months Ended
Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2013	Sep. 30, 2012
Discontinued Operations [Line Items]
Income (loss) from discontinued operations, net of income taxes	$ 8	$ 25	$ (322)	$ 58
Retail Electric and Natural Gas Supply Businesses of Pepco Energy Services [Member]
Discontinued Operations [Line Items]
Operating revenue		76	84	346
Income from operations of discontinued operations, net of income taxes	1	8	4	25
Net gains associated with the accelerated disposition of retail electric and natural gas contracts, net of income taxes			1
Income (loss) from discontinued operations, net of income taxes	$ 1	$ 8	$ 5	$ 25

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Amount of gain (loss), after tax expense or benefit and not previously recognized, resulting from the sale of a business component.

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Amount of sales or other form of revenues attributable to the disposal group, including a component of the entity (discontinued operation), during the reporting period.

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Amount of income (loss) from a disposal group, net of income tax before extraordinary items allocable to noncontrolling interests. Includes, net of tax, income (loss) from operations during the phase-out period, gain (loss) on disposal, provision (or any reversals of earlier provisions) for loss on disposal, and adjustments of a prior period gain (loss) on disposal.

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