Intangible Assets - Amortization Expense Charged to Income for 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	$ 88	$ 88	$ 267	$ 257