v3.10.0.1
Debt - Summary of Effective Interest Rate, Contractual Interest Expense and Amortization of Debt Discount (Detail) - USD ($)
$ in Millions
12 Months Ended
Dec. 31, 2018
Dec. 31, 2017
Dec. 31, 2016
Debt Instrument [Line Items]      
Effective interest rate 0.00% 0.00%  
Amortization of debt discount $ 42 $ 40 $ 34
2019 Cash Convertible Senior Notes [Member]      
Debt Instrument [Line Items]      
Effective interest rate 5.14% 5.14%  
Contractual interest expense $ 12 $ 12  
Amortization of debt discount $ 44 $ 42