Stock-Based Compensation - Stock Option Exercises and Restricted Stock Vesting (Detail) - USD ($) shares in Millions, $ in Millions	6 Months Ended
Jun. 30, 2019	Jun. 30, 2018
Share Based Compensation Shares Authorized Under Stock Option Plans Exercise Price Range [Line Items]
Proceeds from stock option exercises	$ 23.4	$ 31.9
Aggregate intrinsic value	82.8	84.4
Tax benefit realized upon exercise	$ 20.2	$ 20.6
Number of shares exercised	0.6	0.7
Restricted Stock [Member]
Share Based Compensation Shares Authorized Under Stock Option Plans Exercise Price Range [Line Items]
Fair value of shares vested	$ 149.8	$ 148.7
Tax benefit realized upon vesting	$ 35.5	$ 34.3
Number of shares vested	0.8	0.9
Performance Based Restricted Stock [Member]
Share Based Compensation Shares Authorized Under Stock Option Plans Exercise Price Range [Line Items]
Fair value of shares vested	$ 47.5	$ 23.0
Tax benefit realized upon vesting	$ 11.5	$ 5.5
Number of shares vested	0.3	0.1

Amount of tax benefit from vesting of other than stock options granted under share-based compensation arrangement.

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Amount of tax benefit from exercise of stock options granted under share-based compensation arrangement.

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Amount of cash inflow from exercise of stock options granted under share-based compensation arrangement.

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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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Fair value of share-based awards for which the grantee gained the right by satisfying service and performance requirements, to receive or retain shares or units, other instruments, or cash.

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

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