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Use of Collateral (Details) (USD $)
In Millions, unless otherwise specified |
Mar. 31, 2015
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Dec. 31, 2014
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|---|---|---|---|---|---|---|---|---|---|---|
| Use of Collateral [Abstract] | ||||||||||
| Margin deposits | $ 107 | [1] | $ 96 | [1] | ||||||
| Natural gas and power prepayments | 21 | 22 | ||||||||
| Total margin deposits and natural gas and power prepayments with our counterparties | 128 | [2] | 118 | [2] | ||||||
| Letters of credit issued | 459 | 450 | ||||||||
| First priority liens under power and natural gas agreements | 33 | 48 | ||||||||
| First priority liens under interest rate swap agreements | 120 | 116 | ||||||||
| Total letters of credit and first priority liens with our counterparties | 612 | 614 | ||||||||
| Margin deposits held by us posted by our counterparties | 40 | [1],[3] | 47 | [1],[3] | ||||||
| Letters of credit posted with us by our counterparties | 60 | 61 | ||||||||
| Total margin deposits and letters of credit posted with us by our counterparties | 100 | 108 | ||||||||
| Use of Collateral (Textuals) [Abstract] | ||||||||||
| Margin And Prepayment Amounts Included In Other Assets | 13 | 9 | ||||||||
| Margin And Prepayment Amounts Included In Margin Deposits And Other Prepaid Expenses | $ 115 | $ 109 | ||||||||
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