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Discontinued Operations - Operating Results for Retail Electric and Natural Gas Supply Businesses (Parenthetical) (Detail) (Pepco Energy Services [Member], Discontinued Operations [Member], USD $)
In Millions, unless otherwise specified
12 Months Ended
Dec. 31, 2013
Dec. 31, 2012
Dec. 31, 2011
Pepco Energy Services [Member] | Discontinued Operations [Member]
     
Income Statement by Disposal Groups, Including Discontinued Operations [Line Items]      
Discontinued operations, income tax expense $ 3 $ 18 $ 1