Stock-Based Compensation, Option Plans (Details) - Stock Options - USD ($) $ in Millions	3 Months Ended
Mar. 31, 2019	Mar. 31, 2018
Stock-Based Compensation
Total intrinsic value of stock options exercised (in dollars)	$ 70.0	$ 34.3
Total fair value of stock options vested (in dollars)	0.5	$ 0.5
Total compensation cost related to non-vested options not yet recognized (in dollars)	$ 127.3
Weighted average expected amortization period	3 years 3 months

Weighted average period over which unrecognized compensation is expected to be recognized for equity-based compensation plans, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

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-Publisher FASB
-Name Accounting Standards Codification
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-Section 50
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- Definition

Unrecognized cost of unvested options awarded to employees as compensation.

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- Definition

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.

+ References

No definition available.

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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.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-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.

+ References

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