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Income taxes - Unrecognised deferred tax assets (Details) - USD ($)
$ in Millions
 12 Months Ended
Dec. 31, 2021
Dec. 31, 2020
Disclosure of temporary difference, unused tax losses and unused tax credits [line items]    
Deductible temporary differences, basis $ 2,900 $ 2,866
Unused tax credits, basis 0 0
Tax losses carried forward, basis 20,552 23,434
Total unrecognised deferred tax assets, basis 23,452 26,300
Deductible temporary differences, unrecognised deferred tax asset 1,203 1,204
Unused tax credits 264 212
Tax losses carried forward, unrecognised deferred tax asset 5,047 5,677
Total unrecognised deferred tax assets $ 6,514 7,093
Percentage of unrecognised tax losses that can be carried forward indefinitely 22.00%  
Remaining unrecognised tax losses expiry date after 2032  
United States [member]    
Disclosure of temporary difference, unused tax losses and unused tax credits [line items]    
Total unrecognised deferred tax assets $ 4,206 4,649
Angola [member]    
Disclosure of temporary difference, unused tax losses and unused tax credits [line items]    
Total unrecognised deferred tax assets $ 749 $ 740