Consolidated Balance Sheet (Parenthetical) (USD $) In Millions, except Share data | Sep. 30, 2011 | Dec. 31, 2010 |
|---|---|---|
| Property and equipment, at cost, based on the full cost method of accounting for oil and gas properties ($2,346 and $1,658 were excluded from amortization at September 30, 2011 and December 31, 2010, respectively) | $ 2,346 | $ 1,658 |
| Stockholders' equity: | ||
| Preferred stock ($0.01 par value) | $ 0.01 | $ 0.01 |
| Preferred stock (5,000,000 shares authorized) | 5,000,000 | 5,000,000 |
| Preferred stock (no shares issued) | 0 | 0 |
| Common stock ($0.01 par value) | $ 0.01 | $ 0.01 |
| Common stock (200,000,000 shares authorized at September 30, 2011 and December 31, 2010) | 200,000,000 | 200,000,000 |
| Common stock (136,320,031 and 135,910,641 shares issued at September 30, 2011 and December 31, 2010, respectively) | 136,320,031 | 135,910,641 |
| Treasury stock (at cost, 1,721,720 and 1,664,538 shares at September 30, 2011 and December 31, 2010, respectively | 1,721,720 | 1,664,538 |