Income Taxes - Reconciliation of Liabilities Associated with Uncertain Tax Provisions (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Income Tax Disclosure [Abstract]
Balance at beginning of year	$ 1,419	$ 1,285	$ 1,402
Additions based on tax positions related to the current year	132	70	140
Additions for tax positions of prior years	58	119	136
Additions related to acquisitions		127	5
Impact of changes in exchange rates	23	(25)	(78)
Settlements with tax authorities	(41)	(45)	(99)
Reductions for tax positions of prior years	(157)	(85)	(203)
Reductions due to the lapse of the applicable statute of limitations	(41)	(27)	(18)
Balance at end of year	$ 1,393	$ 1,419	$ 1,285