Earnings per share - Basic and Diluted Earnings Per Share (Details) - USD ($) $ / shares in Units, shares in Millions, $ in Millions |
12 Months Ended | ||
|---|---|---|---|
Dec. 31, 2017 |
Dec. 31, 2016 |
Dec. 31, 2015 |
|
| Earnings per share [abstract] | |||
| – ordinary shareholders of the parent company | $ 9,683 | $ 1,299 | $ 12,572 |
| Weighted average number of ordinary shares outstanding (in shares) | 19,972 | 19,753 | 19,380 |
| Effect of dilutive potential ordinary shares (in shares) | 100 | 92 | 137 |
| Adjusted weighted average number of ordinary shares outstanding (in shares) | 20,072 | 19,845 | 19,517 |
| Basic earnings per share (in dollars per share) | $ 0.48 | $ 0.07 | $ 0.65 |
| Diluted earnings per share (in dollars per share) | $ 0.48 | $ 0.07 | $ 0.64 |
| Antidilutive securities (in shares) | 10 | 7 | |