Employee Benefit Plans (Summary of Activity in Corporation's Active Stock Plans) (Detail) - $ / shares	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Ending Balance, Shares Available for Grant	1,452,452
Stock options exercised, Number of Shares	(1,509,121)	(321,266)	(594,231)
Beginning Balance, Non-Vested Weighted-Average Grant-Date Fair Value	$ 10.23	$ 16.97
Ending Balance, Non-Vested Weighted-Average Grant-Date Fair Value		$ 10.23	$ 16.97
Director deferred stock units outstanding [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Beginning Balance, Number of Shares	45,443	38,867	33,224
Granted, number of shares	8,216	6,576	5,643
Ending Balance, Number of Shares	53,659	45,443	38,867
Beginning Balance, Director Deferred, Weighted-Average Grant-Date Fair Value	$ 61.35	$ 59.39	$ 56.22
Granted, Weighted-Average Grant-Date Fair Value	63.25	72.94	78.04
Ending Balance, Director Deferred, Weighted-Average Grant-Date Fair Value	$ 61.48	$ 61.35	$ 59.39
Non-Vested Stock Awards/ Stock Units Outstanding [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Beginning Balance, Number of Shares	173,180	175,490	199,740
Granted, number of shares	132,800	53,990	32,050
Stock awards vested, Number of Shares	(49,130)	(56,300)	(56,300)
Ending Balance, Number of Shares	256,850	173,180	175,490
Beginning Balance, Non-Vested Weighted-Average Grant-Date Fair Value	$ 66.05	$ 60.55	$ 55.32
Granted, Weighted-Average Grant-Date Fair Value	76.07	65.11	78.92
Stock awards vested, weighted-average grant date fair value	54.56	48.00	52.46
Ending Balance, Non-Vested Weighted-Average Grant-Date Fair Value	$ 73.43	$ 66.05	$ 60.55
Performance Shares [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Granted, number of shares	28,420
Employee Stock Option [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Beginning Balance, Number of Shares	5,612,240	5,029,882	4,738,690
Granted, number of shares	0	890,940	917,750
Stock options exercised, Number of Shares	(1,476,841)	(287,326)	(560,291)
Forfeited, Number of Shares	(46,371)	(21,256)	(66,267)
Ending Balance, Number of Shares	4,089,028	5,612,240	5,029,882
Beginning Balance, Weighted-Average Exercise Price	$ 60.30	$ 58.99	$ 54.35
Granted, Weighted-Average Exercise Price		65.11	78.93
Stock options exercised, Weighted-Average Exercise Price	53.40	51.70	52.04
Forfeited, Weighted-Average Exercise Price	71.04	66.72	62.21
Ending Balance, Weighted-Average Exercise Price	$ 62.67	$ 60.30	$ 58.99
Maximum [Member] | Performance Shares [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Granted, number of shares	42,630
Ending Balance, Number of Shares	42,630
Granted, Weighted-Average Grant-Date Fair Value	$ 69.70
Ending Balance, Non-Vested Weighted-Average Grant-Date Fair Value	$ 69.70