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Goodwill and Acquired Intangible Assets - Aggregate Amortization Expense for Acquired Intangible Assets (Detail) - USD ($)
$ in Millions
12 Months Ended
Dec. 31, 2016
Dec. 31, 2015
Dec. 31, 2014
Goodwill and Intangible Assets Disclosure [Abstract]      
Amortization expense - Actual $ 10 $ 40 $ 47
Amortization expense - 2017 7    
Amortization expense - 2018 3    
Amortization expense - 2019 1    
Amortization expense - 2020 $ 0