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Organization (Details) (USD $)
1 Months Ended 3 Months Ended
Jul. 31, 2010
Mar. 31, 2012
Mar. 31, 2011
Organization [Line Items]      
Operating income   $ 139,000,000 $ 149,000,000
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   160,000,000 305,000,000
Operating income   15,000,000 12,000,000
Letters of credit   1,000,000  
Posted cash collateral   $ 92,000,000