Income Taxes - Additional Information (Detail) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016	Dec. 31, 2016
Income Tax Disclosure [Abstract]
Liability for unrecognized tax benefits	$ 429		$ 429		$ 418
Unrecognized tax benefits, accrued interest	40		40		45
Unrecognized tax benefits that would impact effective tax rate	136		136		$ 137
Provision for tax benefits related to settlement of employee awards	4	$ 11	80	$ 129
Reductions in interest (net of tax)	$ 4	17	$ 16	17
Provision for income taxes		$ 51		$ 51