Income from Continuing Operations Per Unrestricted Share - Reconciliation of Numerator and Denominator Used in Calculation (Details) - USD ($) $ / shares in Units, $ in Millions	3 Months Ended	9 Months Ended
Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Schedule of Basic and Diluted Earnings Per Share [Line Items]
Income from Continuing Operations	$ 129.0	$ 92.3	$ 406.4	$ 183.4
Dilutive Effect on Income of Equity-based Compensation Equivalent Shares	0.0	0.0	0.0	0.0
Diluted Income from Continuing Operations Attributed to Unrestricted Shares	$ 128.6	$ 91.9	$ 405.0	$ 182.4
Weighted-Average Unrestricted Shares Outstanding (in shares)	66,622,400	64,580,400	65,621,800	55,925,700
Equity-based Compensation Equivalent Shares (in shares)	585,300	769,100	719,400	569,800
Weighted-Average Unrestricted Shares and Equivalent Shares Outstanding Assuming Dilution (in shares)	67,207,700	65,349,500	66,341,200	56,495,500
Basic Income from Continuing Operations Per Unrestricted Share (in dollars per share)	$ 1.93	$ 1.42	$ 6.17	$ 3.26
Diluted Income from Continuing Operations Per Unrestricted Share (in dollars per share)	$ 1.91	$ 1.40	$ 6.10	$ 3.23
Common Stock
Schedule of Basic and Diluted Earnings Per Share [Line Items]
Income from Continuing Operations	$ 128.6	$ 91.9	$ 405.0	$ 182.4
Participating Awards
Schedule of Basic and Diluted Earnings Per Share [Line Items]
Income from Continuing Operations	$ 0.4	$ 0.4	$ 1.4	$ 1.0

Schedule of Basic and Diluted Earnings Per Share [Line Items]

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Amount of increase (decrease) to net income used for calculating diluted earnings per share (EPS), resulting from the assumed exercise of stock options or restrictive stock units (RSUs).

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Amount after tax of income (loss) from continuing operations attributable to the parent.

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The amount of net income (loss) from continuing operations per each share of common stock or unit outstanding during the reporting period.

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The amount of net income (loss) derived from continuing operations during the period available to each share of common stock or common unit outstanding during the reporting period and to each share or unit that would have been outstanding assuming the issuance of common shares or units for all dilutive potential common shares or units outstanding during the reporting period.

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Additional shares included in the calculation of diluted EPS as a result of the potentially dilutive effect of share based payment arrangements using the treasury stock method.

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Amount, after deduction of tax, noncontrolling interests, dividends on preferred stock and participating securities, and addition from assumption of issuance of common shares for dilutive potential common shares; of income (loss) from continuing operations available to common shareholders.

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The average number of shares or units issued and outstanding that are used in calculating diluted EPS or earnings per unit (EPU), determined based on the timing of issuance of shares or units in the period.

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