Goodwill and Other Intangible Assets - Additional Information (Detail) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Goodwill And Intangible Assets Disclosure [Abstract]
Goodwill deductible for income tax purposes	$ 64		$ 64
Amortization expense, intangible assets	114	$ 107	341	$ 317
Amortization expense, computer software	$ 64	$ 59	$ 190	$ 172