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Interest Expense, Net - Additional Information (Detail) - USD ($)
 12 Months Ended
Dec. 31, 2017
Dec. 31, 2016
Dec. 31, 2015
Net Investment Income [Line Items]      
Capitalized borrowing cost $ 0 $ 0 $ 0
Senior Unsecured Convertible Debt [Member]      
Net Investment Income [Line Items]      
Interest expense 37,000,000 25,000,000 24,000,000
Non-cash interest expense accretion of discount on liability component $ 33,000,000 $ 21,000,000 20,000,000
Issued date of senior unsecured convertible bonds Jul. 31, 2017 Jul. 31, 2014  
Floating Rate Notes [Member]      
Net Investment Income [Line Items]      
Interest income (expense), net $ 6,000,000 $ 6,000,000 $ 6,000,000