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Drilling Units - Additional Information (Detail) - USD ($)
$ in Millions
6 Months Ended 12 Months Ended
Jun. 30, 2018
Jun. 30, 2017
Dec. 31, 2017
Property, Plant and Equipment [Line Items]      
Impairment of long-lived assets $ 414   $ 696
Drilling Unit [Member]      
Property, Plant and Equipment [Line Items]      
Depreciation expense 388 $ 392  
Impairment of long-lived assets $ 414    
Weighted average cost of capital 11.40%    
Equipment [Member]      
Property, Plant and Equipment [Line Items]      
Depreciation expense $ 3 $ 14