Employee Benefit Plans (Summary of Activity in Corporation's Active Stock Plans) (Detail) - $ / shares	12 Months Ended
Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock options exercised, number of shares	(548,238)	(1,150,920)	(1,509,121)
Director deferred stock units outstanding [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Beginning balance, number of shares	53,008	53,659	45,443
Granted, number of shares	6,576	5,447	8,216
Stock awards exercised/vested, number of shares	(10,674)	(6,098)
Ending balance, number of shares	48,910	53,008	53,659
Beginning balance, Director Deferred, weighted-average grant-date fair value	$ 64.87	$ 61.48	$ 61.35
Granted, weighted-average grant-date fair value	109.58	95.37	63.25
Stock awards exercised/vested, weighted-average grant date fair value	63.68	62.29
Ending balance, Director Deferred, weighted-average grant-date fair value	$ 71.14	$ 64.87	$ 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	312,656	256,850	173,180
Granted, number of shares	109,847	99,833	132,800
Stock awards exercised/vested, number of shares	(32,050)	(39,740)	(49,130)
Forfeited/expired, number of shares	(6,656)	(4,287)
Ending balance, number of shares	383,797	312,656	256,850
Beginning balance, non-vested weighted-average grant-date fair value	$ 81.71	$ 73.43	$ 66.05
Granted, weighted-average grant-date fair value	94.81	98.90	76.07
Stock awards exercised/vested, weighted-average grant date fair value	78.92	71.59	54.56
Ending balance, non-vested weighted-average grant-date fair value	85.59	81.71	$ 73.43
Forfeited/expired, weighted-average exercise price	$ 87.60	$ 79.52
Performance Shares [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Granted, number of shares	30,466	24,162	29,240
Employee Stock Option [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Beginning balance, number of shares	2,917,142	4,089,028	5,612,240
Granted, number of shares	0	0	0
Stock options exercised, number of shares	(513,134)	(1,118,122)	(1,476,841)
Forfeited/expired, number of shares	(52,000)	(53,764)	(46,371)
Ending balance, number of shares	2,352,008	2,917,142	4,089,028
Beginning balance, weighted-average exercise price	$ 63.34	$ 62.67	$ 60.30
Stock options exercised, weighted-average exercise price	61.68	60.59	53.40
Forfeited/expired, weighted-average exercise price	70.42	69.78	71.04
Ending balance, weighted-average exercise price	$ 63.55	$ 63.34	$ 62.67
Maximum [Member] \| Performance Shares [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Beginning balance, number of shares	80,106	43,860
Granted, number of shares	45,703	36,246	43,860
Ending balance, number of shares	125,809	80,106	43,860
Beginning balance, non-vested weighted-average grant-date fair value	$ 79.91	$ 69.70
Granted, weighted-average grant-date fair value	87.18	92.27	$ 69.70
Ending balance, non-vested weighted-average grant-date fair value	$ 82.55	$ 79.91	$ 69.70

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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- Definition

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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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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Number of fully vested and expected to vest exercisable options that may be converted into shares under option plan. Includes, but is not limited to, unvested options for which requisite service period has not been rendered but that are expected to vest based on achievement of performance condition, if forfeitures are recognized when they occur.

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Weighted-average exercise price, at which grantee can acquire shares reserved for issuance, for fully vested and expected to vest options outstanding. Includes, but is not limited to, unvested options for which requisite service period has not been rendered but that are expected to vest based on achievement of performance condition, if forfeitures are recognized when they occur.

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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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Weighted average grant-date fair value of options vested.

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

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