The number of equity-based payment instruments, excluding stock (or unit) options, that were forfeited during the reporting period.

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The weighted average fair value at grant date for nonvested equity-based awards issued during the period on other than stock (or unit) option plans (for example, phantom stock or unit plan, stock or unit appreciation rights plan, performance target plan).

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Per share or unit weighted-average fair value of nonvested award under share-based payment arrangement. Excludes share and unit options.

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The number of equity-based payment instruments, excluding stock (or unit) options, that vested during the reporting period.

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The weighted average fair value as of grant date pertaining to an equity-based award plan other than a stock (or unit) option plan for which the grantee gained the right during the reporting period, by satisfying service and performance requirements, to receive or retain shares or units, other instruments, or cash in accordance with the terms of the arrangement.

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The number of shares under options that were cancelled during the reporting period as a result of occurrence of a terminating event specified in contractual agreements pertaining to the stock option plan.

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Number of options outstanding, including both vested and non-vested options.

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Weighted average price at which grantees can acquire the shares reserved for issuance under the stock option plan.

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Weighted average price at which option holders acquired shares when converting their stock options into shares.

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Number of share options (or share units) exercised during the current period.

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Stock-Based Compensation - Summary of Activity in Corporation's Active Stock Plans (Detail) - $ / shares	3 Months Ended		6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock options exercised, Number of Shares	(77,308)	(53,035)	(143,523)	(153,900)
Director deferred stock units outstanding [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Beginning Balance, Number of Shares/Units			55,370
Granted, Number of Units			10,428
Stock Awards exercised/vested, Number of Shares			(12,938)
Ending Balance, Number of Shares/Units	52,860		52,860
Beginning Balance, Weighted-Average Grant-Date Fair Value			$ 74.76
Granted Weighted-Average Grant-Date Fair Value			73.84
Stock Award Exercised/Vested, Weighted Average Grant Date Fair Value			71.09
Ending Balance, Weighted-Average Grant-Date Fair Value	$ 75.47		$ 75.47
Non-Vested Stock Awards/Stock Units Outstanding [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Beginning Balance, Number of Shares/Units			440,647
Granted, Number of Units			458
Forfeited/expired, Number of Shares/Units			(1,840)
Ending Balance, Number of Shares/Units	439,265		439,265
Beginning Balance, Weighted-Average Grant-Date Fair Value			$ 90.22
Granted Weighted-Average Grant-Date Fair Value			65.43
Forfeited/Expired, Weighted-Average Price			89.29
Ending Balance, Weighted-Average Grant-Date Fair Value	$ 90.20		$ 90.20
Stock Options Outstanding [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Beginning Balance, Number of Shares			1,980,866
Stock options exercised, Number of Shares			(88,830)
Forfeited/expired, Number of Shares			(5,052)
Ending Balance, Number of Shares	1,886,984		1,886,984
Beginning Balance, Weighted-Average Exercise Price			$ 64.60
Stock options exercised, Weighted-Average Exercise Price			54.56
Forfeited/expired, Weighted-Average Exercise Price			76.19
Ending Balance, Weighted-Average Exercise Price	$ 65.04		$ 65.04
Maximum [Member] \| Performance Shares [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Beginning Balance, Number of Shares/Units			177,288
Stock Awards exercised/vested, Number of Shares			(41,755)
Forfeited/expired, Number of Shares/Units			(6,894)
Ending Balance, Number of Shares/Units	128,639		128,639
Beginning Balance, Weighted-Average Grant-Date Fair Value			$ 83.48
Stock Award Exercised/Vested, Weighted Average Grant Date Fair Value			69.70
Forfeited/Expired, Weighted-Average Price			81.33
Ending Balance, Weighted-Average Grant-Date Fair Value	$ 88.07		$ 88.07