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Redeemable non-controlling interest - Schedule of Changes in Redeemable Non-controlling Interest (Details) - USD ($)
$ in Millions
12 Months Ended
Sep. 11, 2020
Dec. 31, 2020
Dec. 31, 2019
Increase (Decrease) in Temporary Equity [Roll Forward]      
Acquisition of NCI   $ (31)  
Asia Offshore Drilling Ltd      
Increase (Decrease) in Temporary Equity [Roll Forward]      
Acquisition of NCI $ 31    
Redeemable non-controlling interest      
Increase (Decrease) in Temporary Equity [Roll Forward]      
Beginning balance   57  
Ending balance   0 $ 57
Redeemable non-controlling interest | Asia Offshore Drilling Ltd      
Increase (Decrease) in Temporary Equity [Roll Forward]      
Beginning balance     38
Net loss attributable to redeemable non-controlling interest   (1) (2)
Fair value adjustment   $ (25) $ 21