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Equipment (Details) - USD ($)
$ in Millions
12 Months Ended
Dec. 31, 2020
Dec. 31, 2019
Dec. 31, 2020
Dec. 31, 2019
Dec. 31, 2018
Jul. 01, 2018
Equipment            
Cost            
Opening balance $ 38 $ 34        
Property, Plant and Equipment, Additions 1 4        
Closing balance 39 38        
Cost 39 38 $ 39 $ 38 $ 34  
Accumulated depreciation            
Opening balance (15) (5)        
Depreciation (5) (10)        
Closing balance (20) (15)        
Accumulated depreciation $ (20) $ (15) (20) (15) (5)  
Net book value     $ 19 $ 23 $ 29  
Fresh Start Adjustments            
Accumulated depreciation            
Fresh Start adjustments, net           $ (6)