Stock-Based Compensation - Schedule of Other Stock Option Statistics (Details) - Non-qualified stock options - USD ($) $ / shares in Units, shares in Millions, $ in Millions	12 Months Ended
Dec. 31, 2020	Dec. 31, 2019
Other disclosures
Aggregate intrinsic value of outstanding options	$ 8.3	$ 31.8
Aggregate intrinsic value of exercisable options	5.7	28.0
Total intrinsic value of options exercised	$ 2.5	$ 22.9
Total number of options exercisable (in shares)	0.9	0.9
Weighted average exercise price of options exercisable (in dollars per share)	$ 46.29	$ 41.00
Total unrecognized compensation cost on nonvested options	$ 3.8	$ 1.5

Amount of cost not yet recognized for nonvested award under share-based payment arrangement.

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The number of shares into which fully or partially vested stock options outstanding as of the balance sheet date can be currently converted under the option plan.

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The weighted-average price as of the balance sheet date at which grantees can acquire the shares reserved for issuance on vested portions of options outstanding and currently exercisable under the stock option plan.

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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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Amount by which the current fair value of the underlying stock exceeds the exercise price of options outstanding.

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Amount of difference between fair value of the underlying shares reserved for issuance and exercise price of vested portions of options outstanding and currently exercisable.

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