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Business combination - Narrative (Details) - USD ($)
$ in Millions
Sep. 02, 2021
Nov. 30, 2021
Nov. 02, 2021
Sep. 01, 2021
SeaMex        
Business Acquisition [Line Items]        
Seadrill ownership percentage       50.00%
SeaMex        
Business Acquisition [Line Items]        
Extinguishment of debt $ 400      
Equity interest, acquisition of residual (in percent)   100.00% 50.00%  
Debt securities, allowance for credit loss $ 65