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Use of Collateral (Details) (USD $)
In Millions, unless otherwise specified |
Sep. 30, 2013
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Dec. 31, 2012
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| Use of Collateral [Abstract] | ||||||||||
| Margin deposits | $ 302 | [1] | $ 196 | [1] | ||||||
| Natural gas and power prepayments | 23 | 35 | ||||||||
| Total margin deposits and natural gas and power prepayments with our counterparties | 325 | [2] | 231 | [2] | ||||||
| Letters of credit issued | 505 | 484 | ||||||||
| First priority liens under power and natural gas agreements | 18 | 14 | ||||||||
| First priority liens under interest rate swap agreements | 148 | 206 | ||||||||
| Total letters of credit and first priority liens with our counterparties | 671 | 704 | ||||||||
| Margin deposits held by us posted by our counterparties | 22 | [1],[3] | 11 | [1],[3] | ||||||
| Letters of credit posted with us by our counterparties | 87 | 1 | ||||||||
| Total margin deposits and letters of credit posted with us by our counterparties | 109 | 12 | ||||||||
| Use of Collateral (Textuals) [Abstract] | ||||||||||
| Margin And Prepayment Amounts Included In Other Assets | 18 | 20 | ||||||||
| Margin And Prepayment Amounts Included In Margin Deposits And Other Prepaid Expenses | $ 307 | $ 211 | ||||||||
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