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Acquired Intangible Assets - Aggregate Amortization Expense for Acquired Intangible Assets (Detail) - USD ($)
$ in Millions
 3 Months Ended 12 Months Ended
Mar. 31, 2018
Mar. 31, 2017
Dec. 31, 2017
Goodwill and Intangible Assets Disclosure [Abstract]      
Amortization expense $ 2 $ 2 $ 8
Amortization expense - Remainder of 2018 7    
Amortization expense - 2019 6    
Amortization expense - 2020 4    
Amortization expense - 2021 4    
Amortization expense - 2022 $ 2