Use of Collateral (Details) - USD ($) $ in Millions |
Sep. 30, 2015 |
Dec. 31, 2014 |
|||||||
|---|---|---|---|---|---|---|---|---|---|
| Use of Collateral [Abstract] | |||||||||
| Margin deposits | [1] | $ 167 | $ 96 | ||||||
| Natural gas and power prepayments | 23 | 22 | |||||||
| Total margin deposits and natural gas and power prepayments with our counterparties | [2] | 190 | 118 | ||||||
| Letters of credit issued | 460 | 450 | |||||||
| First priority liens under power and natural gas agreements | 28 | 48 | |||||||
| First priority liens under interest rate swap agreements | 112 | 116 | |||||||
| Total letters of credit and first priority liens with our counterparties | 600 | 614 | |||||||
| Margin deposits held by us posted by our counterparties | [1],[3] | 15 | 47 | ||||||
| Letters of credit posted with us by our counterparties | 125 | 61 | |||||||
| Total margin deposits and letters of credit posted with us by our counterparties | 140 | 108 | |||||||
| Use of Collateral (Textuals) [Abstract] | |||||||||
| Margin And Prepayment Amounts Included In Other Assets | 14 | 9 | |||||||
| Margin And Prepayment Amounts Included In Margin Deposits And Other Prepaid Expenses | $ 176 | $ 109 | |||||||
| |||||||||