Use of Collateral (Details) - USD ($) $ in Millions |
Dec. 31, 2015 |
Dec. 31, 2014 |
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|---|---|---|---|---|---|---|---|---|---|---|---|
| Financial Instruments Owned and Pledged as Collateral [Line Items] | |||||||||||
| Margin Deposit Assets | [1] | $ 89 | $ 96 | ||||||||
| Natural gas and power prepayments | 34 | 22 | |||||||||
| Total margin deposits and natural gas and power prepayments with our counterparties | [2] | 123 | 118 | ||||||||
| Letters of credit issued | 600 | 450 | |||||||||
| First priority liens under power and natural gas agreements | [3] | 382 | 48 | ||||||||
| First priority liens under interest rate swap agreements | 92 | 116 | |||||||||
| Total letters of credit and first priority liens with our counterparties | 1,074 | 614 | |||||||||
| Security Deposit Liability | [1],[4] | 35 | 47 | ||||||||
| Letters of credit posted with us by our counterparties | 24 | 61 | |||||||||
| Total margin deposits and letters of credit posted with us by our counterparties | 59 | 108 | |||||||||
| Use of Collateral (Textuals) [Abstract] | |||||||||||
| Margin And Prepayment Amounts Included In Margin Deposits And Other Prepaid Expenses | 101 | 109 | |||||||||
| Margin And Prepayment Amounts Included In Other Assets | 22 | $ 9 | |||||||||
| Champion Energy [Member] | |||||||||||
| Financial Instruments Owned and Pledged as Collateral [Line Items] | |||||||||||
| First priority liens under power and natural gas agreements | [3] | $ 345 | |||||||||
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