Stock-Based Compensation - Summary of Activity in Corporation's Active Stock Plans (Detail) - $ / shares	6 Months Ended
Jun. 30, 2016	Jun. 30, 2015
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Beginning Balance, Shares Available for Grant	1,589,727
Granted, Shares Available For Grant	(8,216)
Forfeited/expired, Shares Available for Grant	39,192
Ending Balance, Shares Available for Grant	1,620,703
Stock options exercised, Number of Shares	(67,075)	(171,474)
Director deferred stock units outstanding [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Beginning Balance, Number of Shares	45,443
Granted, Number of Shares	8,216
Ending Balance, Number of Shares	53,659
Beginning Balance, Director Deferred, Weighted-Average Grant-Date Fair Value	$ 61.16
Granted, Weighted-Average Grant-Date Fair Value	63.25
Ending Balance, Director Deferred, Weighted-Average Grant-Date Fair Value	$ 61.48
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
Ending Balance, Number of Shares	173,180
Beginning Balance, Weighted-Average Grant-Date Fair Value	$ 66.05
Ending Balance, Weighted-Average Grant-Date Fair Value	$ 66.05
Stock Options Outstanding [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Beginning Balance, Number of Shares	5,612,240
Stock options exercised, Number of Shares	(67,075)
Forfeited/expired, Number of Shares	(39,192)
Ending Balance, Number of Shares	5,505,973
Beginning Balance, Weighted-Average Exercise Price	$ 60.30
Stock options exercised, Weighted-Average Exercise Price	53.46
Forfeited/expired, Weighted-Average Exercise Price	70.84
Ending Balance, Weighted-Average Exercise Price	$ 60.31

Share Based Compensation Arrangement By Share Based Payment Award Options Forfeitures Shares Available for Grant

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Share Based Compensation Arrangement By Share Based Payment Award Options Number Of Shares Available for Grant, Granted

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- Definition

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).

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 718
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (c)(2)(iii)(1)
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The weighted average fair value of nonvested awards on equity-based plans excluding option plans (for example, phantom stock or unit plan, stock or unit appreciation rights plan, revenue or profit achievement stock award plan) for which the employer is contingently obligated to issue equity instruments or transfer assets to an employee who has not yet satisfied service or performance criteria necessary to gain title to proceeds from the sale of the award or underlying shares or units.

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Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

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The difference between the maximum number of shares (or other type of equity) authorized for issuance under the plan (including the effects of amendments and adjustments), and the sum of: 1) the number of shares (or other type of equity) already issued upon exercise of options or other equity-based awards under the plan; and 2) shares (or other type of equity) reserved for issuance on granting of outstanding awards, net of cancellations and forfeitures, if applicable.

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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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Gross number of share options (or share units) granted during the period.

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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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As of the balance sheet date, the weighted-average exercise price for outstanding stock options that are fully vested or expected to vest.

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

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Weighted average price at which grantees could have acquired the underlying shares with respect to stock options that were terminated.

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

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