Earnings Per Share (Details) - USD ($) $ / shares in Units, $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020
Numerator:
Income from continuing operations	$ 94.1	$ 76.0	$ 143.2	$ 140.8
Less: dividends declared	(27.5)	(27.7)	(56.0)	(56.0)
Undistributed earnings	$ 66.6	$ 48.3	$ 87.2	$ 84.8
Percent allocated to common shareholders	99.70%	99.70%	99.70%	99.70%
Undistributed earnings available to common shareholders	$ 66.4	$ 48.2	$ 86.9	$ 84.5
Add: dividends declared on common stock, restricted share units and vested and deferred restricted and performance shares	27.5	27.7	55.9	55.9
Income from continuing operations attributable to common shares	$ 93.9	$ 75.9	$ 142.8	$ 140.4
Denominator (in thousands):
Basic weighted-average shares outstanding (in shares)	52,300,000	54,800,000	52,700,000	55,300,000
Effect of dilutive securities:
Performance awards (in shares)	200,000	200,000	100,000	200,000
Stock options (in shares)	500,000	200,000	500,000	300,000
Denominator for diluted EPS: weighted-average shares outstanding (in shares)	53,000,000.0	55,200,000	53,300,000	55,800,000
Per share income from continuing operations attributable to common shares:
Basic (in dollars per share)	$ 1.79	$ 1.38	$ 2.71	$ 2.54
Diluted (in dollars per share)	$ 1.77	$ 1.37	$ 2.68	$ 2.52
Basic weighted-average shares outstanding (in shares)	52,300,000	54,800,000	52,700,000	55,300,000
Basic weighted-average shares outstanding and unvested restricted shares expected to vest (in shares)	52,500,000	55,000,000.0	52,800,000	55,500,000
Percent allocated to common shareholders	99.70%	99.70%	99.70%	99.70%
Anti-dilutive stock options excluded from EPS calculation
Income (loss) from discontinued operations attributable to common shareholders for basic and diluted earnings per share	$ 5.2	$ (0.6)	$ 8.3	$ (3.6)
Net income attributable to common shareholders for basic and diluted earnings per share	$ 99.2	$ 75.3	$ 151.1	$ 136.9
Anti-dilutive stock options excluded from earnings per share calculation (in shares)	0	500,000	300,000	300,000