Earnings per share - Basic and Diluted Earnings Per Share (Details) - USD ($) $ / shares in Units, shares in Millions, $ in Millions	6 Months Ended
Jun. 30, 2018	Dec. 31, 2017	Jun. 30, 2017
Earnings per share [abstract]
Profit attributable to ordinary shareholders of the parent company	$ 7,173	$ 2,684	$ 6,999
Weighted average number of ordinary shares outstanding (in shares)	19,998	20,027	19,916
Effect of dilutive potential ordinary shares (in shares)	86	104	90
Adjusted weighted average number of ordinary shares outstanding (in shares)	20,084	20,131	20,006
Basic earnings per share (in dollars per share)	$ 0.36	$ 0.13	$ 0.35
Diluted earnings per share (in dollars per share)	$ 0.36	$ 0.13	$ 0.35

The weighted average number of ordinary shares outstanding plus the weighted average number of ordinary shares that would be issued on the conversion of all the dilutive potential ordinary shares into ordinary shares. [Refer: Ordinary shares [member]; Weighted average [member]]

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The amount of profit (loss) attributable to ordinary equity holders of the parent entity (the numerator) divided by the weighted average number of ordinary shares outstanding during the period (the denominator).

+ References

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The amount of profit (loss) attributable to ordinary equity holders of the parent entity (the numerator), divided by the weighted average number of ordinary shares outstanding during the period (the denominator), both adjusted for the effects of all dilutive potential ordinary shares. [Refer: Ordinary shares [member]; Weighted average [member]]

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The number of dilutive potential ordinary shares that relate to the assumed conversion of the entity's convertible instruments.

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The profit (loss) attributable to ordinary equity holders of the parent equity. [Refer: Profit (loss)]

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The number of ordinary shares outstanding at the beginning of the period, adjusted by the number of ordinary shares bought back or issued during the period multiplied by a time-weighting factor.

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