| 2013 | 2012 | 2011 | ||||||||||||||
| Weighted- | Number of | Weighted- | Number of | Weighted- | Number of | |||||||||||
| Average | Shares | Average | Shares | Average | Shares | |||||||||||
| Exercise Price | Under Option | Exercise Price | Under Option | Exercise Price | Under Option | |||||||||||
| Balance at January 1 | $ | 94 | 11,389,721 | $ | 90 | 20,662,322 | $ | 94 | 39,197,728 | |||||||
| Options exercised | 90 | (5,585,127) | 86 | (9,080,170) | 98 | (18,144,309) | ||||||||||
| Options canceled/expired | 86 | (181,643) | 75 | (192,431) | 107 | (391,097) | ||||||||||
| Balance at December 31 | $ | 97 | 5,622,951 | $ | 94 | 11,389,721 | $ | 90 | 20,662,322 | |||||||
| Exercisable at December 31 | $ | 97 | 5,622,951 | $ | 94 | 11,389,721 | $ | 90 | 20,662,322 | |||||||