Discontinued Operations - Operating Results for Retail Electric and Natural Gas Supply Businesses (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 from discontinued operations, net of income taxes	$ 0	$ (11)	$ 0	$ (330)
Discontinued Operations [Member] \| Pepco Energy Services [Member]
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Operating revenue		34		84
Income from operations of discontinued operations, net of income taxes		1		3
Net gains associated with accelerated disposition of retail electric and natural gas contracts, net of income taxes		3		1
Income from discontinued operations, net of income taxes		$ 4		$ 4

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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After tax income (loss) from operations of a business component (exclusive of any gain (loss) on disposal, or provision therefore) during the reporting period, until its disposal.

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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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