Earnings Per Share (Details) (USD $) In Millions, except Per Share data | 3 Months Ended | 9 Months Ended | ||
|---|---|---|---|---|
Sep. 30, 2011 | Sep. 30, 2010 | Sep. 30, 2011 | Sep. 30, 2010 | |
| Income (numerator): | ||||
| Net income - basic and diluted | $ 269 | $ 161 | $ 471 | $ 501 |
| Weighted average shares (denominator): | ||||
| Weighted average shares - basic | 134 | 132 | 134 | 132 |
| Dilution effect of stock options and unvested restricted stock and restricted stock units outstanding at end of period | 1 | 2 | 1 | 2 |
| Weighted average shares - diluted | 135 | 134 | 135 | 134 |
| Basic -- | ||||
| Basic | $ 2.00 | $ 1.22 | $ 3.52 | $ 3.80 |
| Diluted -- | ||||
| Diluted | $ 1.99 | $ 1.20 | $ 3.49 | $ 3.75 |
| Earnings Per Share (Textuals) [Abstract] | ||||
| Incremental shares attributable to the assumed exercise of outstanding stock options and the assumed vesting of unvested restricted stock and restricted stock units | 1.0 | 1.0 | 1.0 | 1.0 |