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Use of Collateral (Details) (USD $)
In Millions, unless otherwise specified |
Dec. 31, 2014
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Dec. 31, 2013
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| Use of Collateral [Abstract] | ||||||||||
| Margin Deposit Assets | $ 96 | [1] | $ 261 | [1] | ||||||
| Natural gas and power prepayments | 22 | 28 | ||||||||
| Total margin deposits and natural gas and power prepayments with our counterparties | 118 | [2] | 289 | [2] | ||||||
| Letters of credit issued | 450 | 488 | ||||||||
| First priority liens under power and natural gas agreements | 48 | 31 | ||||||||
| First priority liens under interest rate swap agreements | 116 | 132 | ||||||||
| Total letters of credit and first priority liens with our counterparties | 614 | 651 | ||||||||
| Security Deposit Liability | 47 | [1],[3] | 5 | [1],[3] | ||||||
| Letters of credit posted with us by our counterparties | 61 | 2 | ||||||||
| Total margin deposits and letters of credit posted with us by our counterparties | 108 | 7 | ||||||||
| Use of Collateral (Textuals) [Abstract] | ||||||||||
| Margin And Prepayment Amounts Included In Other Assets | 9 | 17 | ||||||||
| Margin And Prepayment Amounts Included In Margin Deposits And Other Prepaid Expenses | $ 109 | $ 272 | ||||||||
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