Incentive Compensation Plans Stock Option Activity (Details) - USD ($) $ / shares in Units, shares in Millions, $ in Millions	12 Months Ended
Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Stock-based Payment Award
Intrinsic value of stock options exercised	$ 0.0	$ 0.0	$ 8.8
Proceeds from stock options exercised including taxes withheld	0.0	0.0	12.2
Tax withheld on stock options received	$ 0.0	$ 0.0	$ 4.2
Award Vesting Period - Maximum	3 years
Employee Stock Option
Stock-based Payment Award
Stock options outstanding as of January 1, 2018	0.3
Stock options outstanding as of Jan 1, 2018, Weighted-average exercise price	$ 23.30
Exercised	0.0	0.0	(0.6)
Exercised, weighted-average exercise price	$ 12.77
Stock options outstanding as of December 31, 2018	0.3	0.3
Stock options outstanding as of Dec 31, 2018, Weighted-average exercise price	$ 23.33	$ 23.30
Options outstanding, weighted average remaining contractual term	7 years
Stock options outstanding, aggregate intrinsic value	$ 2.3
Performance-based awards
Stock-based Payment Award
Share-based Compensation Arrangement by Share-based Payment Award, Options, Grants in Period, Weighted Average Grant Date Fair Value	$ 0.0
Share-based Compensation Arrangement by Share-based Payment Award, Options, Grants in Period, Gross	0.0	0.0	0.3

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The cash inflow associated with the amount received from holders exercising their stock options including cash for taxes withheld. This item inherently excludes any excess tax benefit, which the entity may have realized and reported separately.

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Tax Withheld on Stock Options Received

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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.

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

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

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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 price at which option holders acquired shares when converting their stock options into shares.

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Weighted average remaining contractual term for vested portions of options outstanding and currently exercisable or convertible, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

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

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