Use of Collateral (Details) - USD ($) $ in Millions |
Jun. 30, 2015 |
Dec. 31, 2014 |
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|---|---|---|---|---|---|---|---|---|---|
| Use of Collateral [Abstract] | |||||||||
| Margin deposits | [1] | $ 103 | $ 96 | ||||||
| Natural gas and power prepayments | 25 | 22 | |||||||
| Total margin deposits and natural gas and power prepayments with our counterparties | [2] | 128 | 118 | ||||||
| Letters of credit issued | 452 | 450 | |||||||
| First priority liens under power and natural gas agreements | 24 | 48 | |||||||
| First priority liens under interest rate swap agreements | 106 | 116 | |||||||
| Total letters of credit and first priority liens with our counterparties | 582 | 614 | |||||||
| Margin deposits held by us posted by our counterparties | [1],[3] | 53 | 47 | ||||||
| Letters of credit posted with us by our counterparties | 52 | 61 | |||||||
| Total margin deposits and letters of credit posted with us by our counterparties | 105 | 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 | $ 114 | $ 109 | |||||||
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