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Organization (Details) (USD $)
0 Months Ended 3 Months Ended 6 Months Ended
Jun. 01, 2010
Jun. 30, 2011
Jun. 30, 2010
Jun. 30, 2011
Jun. 30, 2010
Operating income   $ 202,000,000 $ 193,000,000 $ 351,000,000 $ 324,000,000
Proceeds from sale of power generation business 1,640,000,000        
Retail Energy Service Business [Member]
         
Operating revenue   231,000,000 401,000,000 536,000,000 898,000,000
Operating income   4,000,000 10,000,000 16,000,000 31,000,000
Letters of credit   62,000,000   62,000,000  
Posted cash collateral   $ 76,000,000   $ 76,000,000