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Drilling Units - Summary Of Net Book Value (Detail) - USD ($)
$ in Millions
6 Months Ended 12 Months Ended
Jun. 30, 2018
Dec. 31, 2017
Property, Plant and Equipment [Line Items]    
Impairment $ (414) $ (696)
Net book value 12,780 13,464
Drilling Unit [Member]    
Property, Plant and Equipment [Line Items]    
Cost 17,452 17,335
Accumulated depreciation (4,507) (4,119)
Impairment (414)  
Net book value $ 12,531 $ 13,216