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Drilling units (Details) - USD ($)
$ in Millions
6 Months Ended 12 Months Ended
Dec. 31, 2018
Jul. 01, 2018
Dec. 31, 2020
Dec. 31, 2019
Cost        
Impairment $ 0 $ (414) $ (4,087) $ 0
Accumulated depreciation        
Impairment of long-lived assets 0 $ 414 4,087 0
Drilling units        
Cost        
Opening balance     7,048 6,890
Additions     147 158
Impairment     (4,087)  
Closing balance 6,890   3,108 7,048
Accumulated depreciation        
Opening balance     (647) (231)
Depreciation     (341) (416)
Closing balance (231)   (988) (647)
Net book value $ 6,659   2,120 6,401
Impairment of long-lived assets     4,087  
Drilling units leased to others | Ship Finance SPV's        
Accumulated depreciation        
Net book value     484 784
Drilling units leased to others | Gulfdrill        
Accumulated depreciation        
Net book value     $ 151 $ 53