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Organization (Detail) (USD $)
In Millions, unless otherwise specified
1 Months Ended 3 Months Ended 12 Months Ended
Jul. 31, 2010
Dec. 31, 2012
Sep. 30, 2012
Jun. 30, 2012
Mar. 31, 2012
Dec. 31, 2011
Sep. 30, 2011
Jun. 30, 2011
Mar. 31, 2011
Dec. 31, 2012
Dec. 31, 2011
Dec. 31, 2010
Organization [Line Items]                        
Operating Income   $ 115 $ 264 $ 152 $ 139 $ 91 $ 195 $ 202 $ 149 $ 670 $ 637 $ 624
Proceeds from sale of power generation business 1,640                     1,640
Subsidiary of Common Parent [Member] | Pepco Energy Services [Member]
                       
Organization [Line Items]                        
Operating revenue                   418 962 1,609
Operating Income                   46 11 59
Letters of credit   1               1    
Posted net cash collateral   $ 25               $ 25