Share-Based Compensation Plans - Stock Options Granted, Vested, and Exercised (Detail) - USD ($) $ / shares in Units, $ in Millions	12 Months Ended
Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Disclosure of Compensation Related Costs, Share-based Payments [Abstract]
Weighted Average Grant-Date Per Share Fair Value of Stock Options Granted (in dollars per share)	$ 0.00	$ 19.18	$ 14.84
Grant-Date Fair Value of Stock Options Vested	$ 8.1	$ 7.3	$ 9.6
Stock Options Exercised
Intrinsic Value as of Exercise Date	28.5	74.7	83.9
Cash Received	32.6	108.0	233.8
Tax Deduction Benefits Realized	$ 27.7	$ 73.1	$ 80.0

Employee Service Share Based Compensation Tax Benefit Realized From Exercise Of Stock Option

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- Definition

Share Based Compensation Arrangement by Share Based Payment Award, Options, Exercises in Period [Abstract]

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

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 718
-SubTopic 10
-Section 50
-Paragraph 2A
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=109197908&loc=SL79508275-113901

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-Publisher FASB
-Name Accounting Standards Codification
-Topic 230
-SubTopic 10
-Section 45
-Paragraph 14
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-URI http://asc.fasb.org/extlink&oid=109223946&loc=d3e3255-108585

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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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Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 718
-SubTopic 10
-Section 50
-Paragraph 2
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-URI http://asc.fasb.org/extlink&oid=109197908&loc=d3e5070-113901

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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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-Publisher FASB
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- Definition

Fair value of options vested. Excludes equity instruments other than options, for example, but not limited to, share units, stock appreciation rights, restricted stock.

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