Stock-Based Compensation (Stock Options Outstanding, Exercisable and Activity) (Detail) - USD ($) $ / shares in Units, $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Number of Shares
Beginning Balance	3,881,566
Granted	642,037
Exercised	(856,900)
Forfeited/Expired	(91,078)
Ending Balance	3,575,625	3,881,566
Vested or expected to vest, at end of period	3,530,023
Exercisable, at end of period	1,677,087
Weighted Average Exercise Price
Beginning Balance (in dollars per share)	$ 75.84
Granted (in dollars per share)	101.53
Exercised (in dollars per share)	61.10
Forfeited/Expired (in dollars per share)	101.36
Ending Balance (in dollars per share)	83.34	$ 75.84
Vested or expected to vest, at end of period (in dollars per share)	83.05
Exercisable, at end of period (in dollars per share)	$ 60.13
Weighted Average Remaining Contractual Life (in years)
Outstanding	6 years 5 months	6 years 6 months
Vested or expected to vest, at end of period	6 years 5 months
Exercisable, at end of period	4 years 5 months
Intrinsic Value (in millions)
Outstanding	$ 120	$ 86
Vested or expected to vest, at end of period	120
Exercisable, at end of period	$ 95