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Organization (Detail) (USD $)
1 Months Ended 3 Months Ended 6 Months Ended
Jul. 31, 2010
Jun. 30, 2012
Jun. 30, 2011
Jun. 30, 2012
Jun. 30, 2011
Organization [Line Items]          
Operating income   $ 152,000,000 $ 202,000,000 $ 291,000,000 $ 351,000,000
Proceeds from sale of power generation business 1,640,000,000        
Subsidiary of Common Parent [Member] | Pepco Energy Services [Member]
         
Organization [Line Items]          
Operating revenue   112,000,000 233,000,000 273,000,000 543,000,000
Operating income   16,000,000 4,000,000 31,000,000 16,000,000
Letters of credit   1,000,000   1,000,000  
Posted cash collateral   $ 61,000,000   $ 61,000,000