Accounts Receivable (Details) (USD $) In Millions | Sep. 30, 2011 | Dec. 31, 2010 |
|---|---|---|
| Accounts Receivable | ||
| Total accounts receivable | $ 322 | $ 354 |
Revenue [Member] | ||
| Accounts Receivable | ||
| Total accounts receivable | 231 | 199 |
Joint interest [Member] | ||
| Accounts Receivable | ||
| Total accounts receivable | 77 | 133 |
Other accounts receivable [Member] | ||
| Accounts Receivable | ||
| Total accounts receivable | 15 | 23 |
Allowance For Doubtful Accounts [Member] | ||
| Accounts Receivable | ||
| Total accounts receivable | $ (1) | $ (1) |