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Income taxes - Significant components of income tax expense (Details) - USD ($)
$ in Millions
 12 Months Ended
Dec. 31, 2020
Dec. 31, 2019
Dec. 31, 2018
Major components of tax (expense) income [abstract]      
Current income tax expense in respect of current year $ (1,115) $ (7,892) $ (10,724)
Prior period adjustments 313 69 (49)
Current income tax expense (802) (7,822) (10,773)
Origination and reversal of temporary differences (648) 410 (1,359)
Recognition of previously unrecognised deferred tax assets 130 0 923
Change in tax regulations (12) (6) (28)
Prior period adjustments 94 (23) (99)
Deferred tax expense (435) 381 (563)
Income tax expense $ (1,237) $ (7,441) $ (11,335)