Goodwill and Acquired Intangible Assets - Aggregate Amortization Expense for Acquired Intangible Assets (Detail) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2015	Sep. 30, 2014
Goodwill and Intangible Assets Disclosure [Abstract]
Amortization expense	$ 10	$ 12	$ 32	$ 35
Amortization expense - Remainder of 2015	44		44
Amortization expense - 2016	36		36
Amortization expense - 2017	28		28
Amortization expense - 2018	16		16
Amortization expense - 2019	14		14
Amortization expense - 2020	$ 7		$ 7