v3.2.0.727
Variable Interest Entities and Unconsolidated Investments in Power Plants Condensed Financial Statements (Details) - USD ($)
$ in Millions
 3 Months Ended 6 Months Ended
Jun. 30, 2015
Jun. 30, 2014
Jun. 30, 2015
Jun. 30, 2014
Operating revenues $ 1,442 $ 1,939 $ 3,088 $ 3,904
Costs and Expenses 1,248 1,614 2,733 3,444
Income from operations 201 329 367 473
Net income (loss) 21 141 14 128
Interest expense, net of interest income 157 167 310 332
Other (income) expense, net $ 5 $ 6 7 16
Greenfield and Whitby [Member]        
Operating revenues     98 149
Costs and Expenses     66 111
Income from operations     32 38
Net income (loss)     23 26
Interest expense, net of interest income     10 12
Other (income) expense, net     $ (1) $ 0