Stock Compensation Plans (Details) - USD ($) $ / shares in Units, shares in Millions, $ in Millions	3 Months Ended	6 Months Ended
Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Stock-Based Compensation Plans
Stock-based compensation expense	$ 5.3	$ 11.6	$ 17.8	$ 25.3
Options granted (shares)			0.5
Options granted exercise price (in dollars per share)			$ 26.20
Performance-based restricted stock units and Restricted stock units granted (in shares)			2.4
Performance-based restricted stock units and Restricted stock units weighted average grant date fair value (in dollars per share)			$ 25.93
Number of options outstanding (in shares)	4.9		4.9
Exercise price of options outstanding (in dollars per share)	$ 19.13		$ 19.13
Number of options exercisable (in shares)	3.8		3.8
Exercise price of options exercisable (in dollars per share)	$ 18.41		$ 18.41
Number of non-vested Performance-based restricted stock units and Restricted stock units (in shares)	7.1		7.1
Grant date fair value of Performance-based restricted stock units and Restricted stock units (in dollars per share)	$ 20.83		$ 20.83

Amount of expense for award under share-based payment arrangement. Excludes amount capitalized.

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The number of grants made during the period on other than stock (or unit) option plans (for example, phantom stock or unit plan, stock or unit appreciation rights plan, performance target plan).

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The weighted average fair value at grant date for nonvested equity-based awards issued during the period on other than stock (or unit) option plans (for example, phantom stock or unit plan, stock or unit appreciation rights plan, performance target plan).

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The number of non-vested equity-based payment instruments, excluding stock (or unit) options, that validly exist and are outstanding as of the balance sheet date.

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Per share or unit weighted-average fair value of nonvested award under share-based payment arrangement. Excludes share and unit options.

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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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Gross number of share options (or share units) granted during the period.

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Number of options outstanding, including both vested and non-vested options.

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Weighted average price at which grantees can acquire the shares reserved for issuance under the stock option plan.

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Weighted average per share amount at which grantees can acquire shares of common stock by exercise of options.

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