Employee Benefit Plans (Summary of Activity in Corporation's Active Stock Plans) (Detail) - $ / shares	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Beginning Balance, Shares Available for Grant	2,004,977	2,894,153	1,188,963
Authorized, shares available for grant	515,000	0	2,293,660
Granted, Shares Available for Grant	(951,506)	(955,443)	(635,360)
Forfeited, Shares Available for Grant	21,256	66,267	46,890
Ending Balance, Shares Available for Grant	1,589,727	2,004,977	2,894,153
Stock options exercised, Number of Shares	(321,266)	(594,231)	(1,319,786)
Beginning Balance, Non-Vested Weighted-Average Grant-Date Fair Value	$ 16.97	$ 13.74
Ending Balance, Non-Vested Weighted-Average Grant-Date Fair Value	$ 10.23	$ 16.97	$ 13.74
Director deferred stock units outstanding [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Beginning Balance, Number of Shares	38,867	33,224	27,724
Granted, number of shares	6,576	5,643	5,500
Ending Balance, Number of Shares	45,443	38,867	33,224
Beginning Balance, Director Deferred, Weighted-Average Grant-Date Fair Value	$ 59.39	$ 56.22	$ 55.46
Granted, Weighted-Average Grant-Date Fair Value	72.94	78.04	60.07
Ending Balance, Director Deferred, Weighted-Average Grant-Date Fair Value	$ 61.35	$ 59.39	$ 56.22
Non-Vested Stock Awards/ Stock Units Outstanding [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Beginning Balance, Number of Shares	175,490	199,740	188,560
Granted, number of shares	53,990	32,050	38,010
Stock awards vested, Number of Shares	(56,300)	(56,300)	(26,830)
Ending Balance, Number of Shares	173,180	175,490	199,740
Beginning Balance, Non-Vested Weighted-Average Grant-Date Fair Value	$ 60.55	$ 55.32	$ 51.67
Granted, Weighted-Average Grant-Date Fair Value	65.11	78.92	71.39
Stock awards vested, Weighted-Average Grant-Date Fair Value	48.00	52.46	50.64
Ending Balance, Non-Vested Weighted-Average Grant-Date Fair Value	$ 66.05	$ 60.55	$ 55.32
Employee Stock Option [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Beginning Balance, Number of Shares	5,029,882	4,738,690	5,513,516
Granted, number of shares	890,940	917,750	591,850
Stock options exercised, Number of Shares	(287,326)	(560,291)	(1,319,786)
Forfeited, Number of Shares	(21,256)	(66,267)	(46,890)
Ending Balance, Number of Shares	5,612,240	5,029,882	4,738,690
Beginning Balance, Weighted-Average Exercise Price	$ 58.99	$ 54.35	$ 51.94
Granted, Weighted-Average Exercise Price	65.11	78.93	71.38
Stock options exercised, Weighted-Average Exercise Price	51.70	52.04	52.02
Forfeited, Weighted-Average Exercise Price	66.72	62.21	46.05
Ending Balance, Weighted-Average Exercise Price	$ 60.30	$ 58.99	$ 54.35