Share-Based Compensation (Detail) (USD $) Share data in Millions, except Per Share data, unless otherwise specified	3 Months Ended
Mar. 31, 2015 plan	Mar. 31, 2014
Share-based compensation
Number of share-based compensation plans	1
Shares available for future grants	2.4
Compensation cost recognized for share-based awards	$ 6,200,000	$ 5,400,000
Total income tax benefit recognized for share-based compensation arrangements	2,600,000	2,300,000
Cash received from the exercise of stock options	21,320,000	13,207,000
Actual tax benefit realized for the tax deductions from stock option exercises	3,400,000	1,700,000
Stock options
Share-based compensation, fair value
Weighted-average volatility (as a percent)	26.66%	27.35%
Dividend yield (as a percent)	1.55%	1.79%
Expected term	6 years 22 days	6 years 26 days
Risk-free interest rate (as a percent)	1.78%	1.99%
Weighted-average grant-date fair values of options granted (in dollars per share)	$ 21.80	$ 17.94
Total intrinsic value of options exercised	$ 8,200,000	$ 4,000,000

The number of share-based compensation plans approved by the entity's shareholders.

No definition available.

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Represents the expense recognized during the period arising from equity-based compensation arrangements (for example, shares of stock, unit, stock options or other equity instruments) with employees, directors and certain consultants qualifying for treatment as employees.

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The total recognized tax benefit related to compensation cost for equity-based payment arrangements recognized in income during the period.

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- Definition

Disclosure of the aggregate tax benefit realized from the exercise of stock options and the conversion of similar instruments during the annual period.

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- Definition

The cash inflow associated with the amount received from holders exercising their stock options. This item inherently excludes any excess tax benefit, which the entity may have realized and reported separately.

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-Glossary Financing Activities

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The estimated dividend rate (a percentage of the share price) to be paid (expected dividends) to holders of the underlying shares over the option's term.

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Expected term of share-based compensation awards, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

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The risk-free interest rate assumption that is used in valuing an option on its own shares.

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Weighted average expected volatility rate of share-based compensation awards.

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- Definition

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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- Definition

Amount of accumulated difference between fair value of underlying shares on dates of exercise and exercise price on options exercised (or share units converted) into shares.

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- Definition

The weighted average grant-date fair value of options granted during the reporting period as calculated by applying the disclosed option pricing methodology.

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