Variable Interest Entities and Unconsolidated Investments in Power Plants Variable Interest Entities and Unconsolidated Investments in Power Plants Condensed Financial Statements (Details) - USD ($) $ in Millions |
3 Months Ended | 6 Months Ended | ||
|---|---|---|---|---|
Jun. 30, 2016 |
Jun. 30, 2015 |
Jun. 30, 2016 |
Jun. 30, 2015 |
|
| Condensed Financial Statements, Captions [Line Items] | ||||
| Operating revenues | $ 1,164 | $ 1,442 | $ 2,779 | $ 3,088 |
| Operating expenses | 1,027 | 1,248 | 2,646 | 2,733 |
| Income from operations | 140 | 201 | 143 | 367 |
| Interest expense, net of interest income | (156) | (157) | (312) | (310) |
| Other (income) expense, net | (7) | (5) | (13) | (7) |
| Net income (loss) | $ (24) | $ 21 | (218) | 14 |
| Greenfield and Whitby [Member] | ||||
| Condensed Financial Statements, Captions [Line Items] | ||||
| Operating revenues | 75 | 98 | ||
| Operating expenses | 43 | 66 | ||
| Income from operations | 32 | 32 | ||
| Interest expense, net of interest income | 8 | 10 | ||
| Other (income) expense, net | 3 | (1) | ||
| Net income (loss) | $ 21 | $ 23 | ||