Employee Benefit Plans (Summary of Activity in Corporation's Active Stock Plans) (Detail) - $ / shares	12 Months Ended
	Dec. 31, 2025	Dec. 31, 2024	Dec. 31, 2023
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock options exercised, number of shares	(344,237)	(589,782)	(267,357)
Director deferred stock units outstanding [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Ending balance, number of shares/units	61,539	52,779	54,164
Beginning balance, number of shares/units	52,779	54,164	45,661
Ending balance, weighted-average grant-date fair value	$ 98.38	$ 95.37	$ 89.71
Beginning balance, weighted-average grant-date fair value	$ 95.37	$ 89.71	$ 87.15
Granted in period, number of shares/units	8,760	7,997	8,503
Granted in period, weighted-average grant-date fair value	$ 116.47	$ 116.84	$ 103.47
Stock awards exercised/vested in period, number of shares		(9,382)
Stock awards exercised/vested in period, weighted-average grant date fair value		$ 80.99
Non-Vested Stock Awards/ Stock Units Outstanding [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Ending balance, number of shares/units	586,298	507,862	566,806
Beginning balance, number of shares/units	507,862	566,806	465,319
Ending balance, weighted-average grant-date fair value	$ 111.39	$ 113.72	$ 99.77
Beginning balance, weighted-average grant-date fair value	$ 113.72	$ 99.77	$ 105.36
Granted in period, number of shares/units	201,569	176,892	217,561
Granted in period, weighted-average grant-date fair value	$ 123.27	$ 129.44	$ 85.39
Stock awards exercised/vested in period, number of shares	(114,675)	(232,617)	(108,920)
Stock awards exercised/vested in period, weighted-average grant date fair value	$ 142.54	$ 91.78	$ 94.00
Forfeited/expired in period, number of shares/units	(8,458)	(3,219)	(7,154)
Forfeited/expired in period, weighted-average grant date fair value	$ 112.11	$ 106.74	$ 114.53
Share-based Payment Arrangement, Option [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Ending balance, number of shares	0	183,976	485,941
Beginning balance, number of shares	183,976	485,941	616,227
Ending balance, weighted-average exercise price	$ 0	$ 65.11	$ 71.25
Beginning balance, weighted-average exercise price	$ 65.11	$ 71.25	$ 71.27
Stock options exercised, number of shares	(183,476)	(301,965)	(130,286)
Stock options exercised, weighted-average exercise price	$ 65.11	$ 74.98	$ 71.37
Share-Based Compensation Arrangement by Share-Based Payment Award, Options, Forfeitures in Period	(500)
Share-Based Compensation Arrangement by Share-Based Payment Award, Options, Forfeitures and Expirations in Period, Weighted Average Exercise Price	$ 65.11
Maximum [Member] | Performance Shares [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Ending balance, number of shares/units	219,512	230,657	267,054
Beginning balance, number of shares/units	230,657	267,054	213,749
Ending balance, weighted-average grant-date fair value	$ 101.23	$ 103.65	$ 89.99
Beginning balance, weighted-average grant-date fair value	$ 103.65	$ 89.99	$ 96.20
Granted in period, number of shares/units	34,941	32,334	99,710
Granted in period, weighted-average grant-date fair value	$ 111.95	$ 119.17	$ 74.71
Stock awards exercised/vested in period, number of shares	(46,086)	(45,818)	(28,151)
Stock awards exercised/vested in period, weighted-average grant date fair value	$ 121.46	$ 57.89	$ 85.74
Forfeited/expired in period, number of shares/units		(22,913)	(18,254)
Forfeited/expired in period, weighted-average grant date fair value		$ 57.89	$ 85.74