Earnings Per Share (Details) - USD ($) $ / shares in Units, shares in Millions, $ in Millions	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Net Income (Loss) Attributable to Parent [Abstract]
Income from continuing operations	$ 387.0	$ 325.7	$ 457.8
Less: dividends declared	(112.7)	(112.7)	(102.9)
Undistributed earnings	$ 274.3	$ 213.0	$ 354.9
Percent allocated to common stockholders	99.70%	99.70%	99.70%
Undistributed earnings available to common shareholders	$ 273.5	$ 212.4	$ 353.8
Add: dividends declared to common shares, restricted share units and vested and deferred restricted and performance shares	112.4	112.2	102.7
Income from continuing operations attributable to common stockholders	$ 385.9	$ 324.6	$ 456.5
Shares:
Basic weighted-average shares outstanding (in shares)	52.5	54.5	56.9
Effect of dilutive securities:
Performance awards (in shares)	0.2	0.3	0.2
Stock options (in shares)	0.5	0.2	0.4
Diluted weighted-average shares outstanding (in shares)	53.2	55.0	57.5
Per share income from continuing operations attributable to common shares:
Basic (in dollars per share)	$ 7.35	$ 5.95	$ 8.02
Diluted (in dollars per share)	$ 7.26	$ 5.90	$ 7.93
Basic weighted-average shares outstanding (in shares)	52.5	54.5	56.9
Basic weighted-average shares outstanding and unvested restricted shares expected to vest (in shares)	52.6	54.7	57.1
Percent allocated to common stockholders	99.70%	99.70%	99.70%
Anti-dilutive stock options excluded from EPS calculation
Income (loss) from discontinued operations attributable to common stockholders for basic and dilutive earnings per share	$ 34.6	$ (5.6)	$ 15.0
Net income attributable to common stockholders for basic and diluted earnings per share	$ 420.5	$ 319.0	$ 471.5
Antidilutive stock options excluded from earnings per share calculation (in shares)	0.1	0.3	0.0