| Million shares | 2017 | 2016 | 2015 | |||||||||
| Common | Common | Common | ||||||||||
Issued shares at December 31, net of treasury shares (i) | 15,705.8 | 15,696.6 | 15,696.1 | |||||||||
| Effect of shares options | 132.2 | 126.5 | 124.0 | |||||||||
| Weighted average number of shares (diluted) at December 31 | 15,838.0 | 15,823.1 | 15,820.1 | |||||||||