Share-Based Compensation - Summary of Stock Option Activity (Detail) $ / shares in Units, shares in Thousands, $ in Millions	12 Months Ended
	Dec. 31, 2018 USD ($) $ / shares shares
Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]
Outstanding stock options, Beginning balance | shares	7,257
Options granted | shares	2,027
Options exercised | shares	(1,136)
Options forfeited | shares	(326)
Options expired | shares	(59)
Outstanding stock options, Ending Balance | shares	7,763
Number of outstanding options, Vested or expected to vest | shares	7,503
Exercisable, Stock options | shares	4,159
Outstanding Weighted average exercise price, Beginning Balance | $ / shares	$ 93.83
Options granted, Weighted average exercise price | $ / shares	116.23
Options exercised, Weighted average exercise price | $ / shares	82.80
Options forfeited, Weighted average exercise price | $ / shares	115.11
Options expired, Weighted average exercise price | $ / shares	108.97
Outstanding Weighted average exercise price, ending Balance | $ / shares	100.29
Outstanding Weighted average exercise price, Vested or expected to vest | $ / shares	99.76
Exercisable, Weighted average exercise price | $ / shares	$ 87.57
Weighted Average Remaining Contractual Life, Outstanding at December 31, 2018	6 years 7 months 6 days
Weighted Average Remaining Contractual Life, Vested or expected to vest as of December 31, 2018	6 years 6 months
Weighted Average Remaining Contractual Life, Exercisable at December 31, 2018	5 years
Intrinsic Value, Outstanding at December 31, 2018 | $	$ 82.0
Intrinsic Value, Vested or expected to vest as of December 31, 2018 | $	81.9
Intrinsic Value, Exercisable at December 31, 2018 | $	$ 80.9