Use of Collateral (Details) (USD $) In Millions | Sep. 30, 2011 | Dec. 31, 2010 | ||||||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Use of Collateral [Abstract] | ||||||||||||||
| Margin deposits | $ 182 | [1] | $ 162 | [1] | ||||||||||
| Natural gas and power prepayments | 38 | 43 | ||||||||||||
| Total margin deposits and natural gas and power prepayments with our counterparties | 220 | [2] | 205 | [2] | ||||||||||
| Letters of credit issued | 524 | [3] | 588 | [3] | ||||||||||
| First priority liens under power and natural gas agreements | [4] | [4] | ||||||||||||
| First priority liens under interest rate swap agreements | 364 | 356 | ||||||||||||
| Total letters of credit and first priority liens with our counterparties | 888 | 944 | ||||||||||||
| Margin deposits held by us posted by our counterparties | 5 | [1],[5] | 6 | [1],[5] | ||||||||||
| Letters of credit posted with us by our counterparties | 15 | 66 | ||||||||||||
| Total margin deposits and letters of credit posted with us by our counterparties | 20 | 72 | ||||||||||||
| Use of Collateral (Textuals) [Abstract] | ||||||||||||||
| Amounts included in other assets on our BS | 21 | 22 | ||||||||||||
| Amounts included in margin deposits and other prepaid expenses on our BS | 199 | 183 | ||||||||||||
| Back-stopped amount of letters of credit used for commodity procurement and risk management activities | 63 | |||||||||||||
| Fair value of commodity instruments collateralized by first priority liens | $ 75 | $ 193 | ||||||||||||
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