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Drilling units - Additional Information (Details) - USD ($)
$ in Millions
6 Months Ended 12 Months Ended
Dec. 31, 2018
Jul. 01, 2018
Dec. 31, 2019
Dec. 31, 2017
Jul. 02, 2018
Drilling units [Line Items]          
Impairment of long-lived assets $ 0 $ 414 $ 0 $ 696  
Fresh Start Adjustments          
Drilling units [Line Items]          
Adjustments, increase (decrease), Drilling units   (5,734)      
Drilling units          
Drilling units [Line Items]          
Impairment of long-lived assets   414      
Net book value 6,659 12,531 6,401 13,216 $ 6,797
Cost 6,890 17,038 7,048 17,335 6,797
Accumulated depreciation $ 231 4,507 647 $ 4,119 $ 0
Drilling units | West Castor          
Drilling units [Line Items]          
Net book value     53    
Cost     72    
Accumulated depreciation     $ 19    
Drilling units | Fresh Start Adjustments          
Drilling units [Line Items]          
Adjustments, increase (decrease), Drilling units   $ (5,734)