Stock-Based Compensation - Analysis of Option Activity (Detail) - $ / shares	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Options
Options Outstanding-beginning of year (in shares)	6,973,591	7,734,841	7,889,321
Options Exercised (in shares)	(1,661,808)	(2,184,169)	(1,576,485)
Options Expired and forfeited (in shares)	(26,488)	(8,518)	(95,621)
Options Outstanding-end of year (in shares)	6,753,801	6,973,591	7,734,841
Options Exercisable at end of year (in shares)	2,928,979	3,115,847	3,774,061
Share-based Compensation Arrangement by Share-based Payment Award, Options, Forfeitures and Expirations in Period, Weighted Average Exercise Price [Abstract]
Outstanding-beginning of year, weighted average exercise price (in dollars per share)	$ 44.64	$ 38.84	$ 32.91
Options exercised in the period - weighted average exercise price (in dollars per share)	36.84	28.08	22.81
Options expired and forfeited in the period - weighted average exercise price (in dollars per share)	57.94	39.35	48.85
Outstanding-end of year, weighted average exercise price (in dollars per share)	53.59	44.64	38.84
Exercisable at end of year, weighted average exercise price (in dollars per share)	$ 43.79	$ 36.81	$ 29.37
7-year term
Options
Options Granted (in shares)	933,286	834,212	1,220,751
Share-based Compensation Arrangement by Share-based Payment Award, Options, Forfeitures and Expirations in Period, Weighted Average Exercise Price [Abstract]
Options granted in the period- weighted average exercise price (in dollars per share)	$ 77.19	$ 50.78	$ 53.62
10-year term
Options
Options Granted (in shares)	535,220	597,225	296,875
Share-based Compensation Arrangement by Share-based Payment Award, Options, Forfeitures and Expirations in Period, Weighted Average Exercise Price [Abstract]
Options granted in the period- weighted average exercise price (in dollars per share)	$ 77.26	$ 50.64	$ 53.61