Adoption of New Accounting Standards and Reclassifications (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Change in Accounting Estimate [Line Items]
Increase to net cash provided by operating activities	$ 3,180	$ 3,006	$ 2,528
Increase to net cash used in financing activities	$ (1,811)	(1,081)	(2,185)
Excess Tax Benefits Or Deficiencies [Member] | Accounting Standards Update 2016-09 [Member]
Change in Accounting Estimate [Line Items]
Increase to net cash provided by operating activities		28	15
Increase to net cash used in financing activities		(28)	(15)
Tax Payments Associated with Equity Based Compensation Transactions [Member] | Accounting Standards Update 2016-09 [Member]
Change in Accounting Estimate [Line Items]
Increase to net cash provided by operating activities		18	15
Increase to net cash used in financing activities		$ (18)	$ (15)