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Taxation - Additional Information (Detail) - USD ($)
$ in Millions
6 Months Ended
Jun. 30, 2018
Jun. 30, 2017
Transactions with Third Party [Line Items]    
Increase in income tax expense $ 48  
Tax expense 18  
Income tax expense (benefit) 36 $ (12)
Increase in uncertain tax position 8  
Secretariat of the Federal Revenue Bureau of Brazil [Member]    
Transactions with Third Party [Line Items]    
Income tax examination, estimate of possible loss 161  
Nigerian tax authorities [member]    
Transactions with Third Party [Line Items]    
Income tax examination, estimate of possible loss $ 171