Earnings Per Share (Details) - USD ($) $ / shares in Units, shares in Millions, $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2022	Jun. 30, 2021	Jun. 30, 2022	Jun. 30, 2021
Numerator:
Income from continuing operations	$ 295.9	$ 94.1	$ 490.2	$ 143.2
Less: dividends declared	(28.0)	(27.5)	(56.7)	(56.0)
Undistributed earnings	$ 267.9	$ 66.6	$ 433.5	$ 87.2
Percent allocated to common stockholders	99.70%	99.70%	99.70%	99.70%
Undistributed earnings allocated to common stockholders	$ 267.2	$ 66.4	$ 432.4	$ 86.9
Add: dividends declared to common shares, restricted share units and vested and deferred restricted and performance shares	27.9	27.5	56.6	55.9
Income from continuing operations attributable to common stockholders	$ 295.1	$ 93.9	$ 489.0	$ 142.8
Denominator (in thousands):
Basic weighted-average shares outstanding (in shares)	51.8	52.3	52.0	52.7
Effect of dilutive securities:
Performance awards (in shares)	0.2	0.2	0.2	0.1
Stock options (in shares)	0.5	0.5	0.5	0.5
Diluted weighted-average shares outstanding (in shares)	52.5	53.0	52.7	53.3
Per share income from continuing operations attributable to common shares:
Basic (in dollars per share)	$ 5.70	$ 1.79	$ 9.41	$ 2.71
Diluted (in dollars per share)	$ 5.62	$ 1.77	$ 9.28	$ 2.68
Basic weighted-average shares outstanding (in shares)	51.8	52.3	52.0	52.7
Basic weighted-average shares outstanding and unvested restricted shares expected to vest (in shares)	51.9	52.5	52.1	52.8
Percent allocated to common stockholders	99.70%	99.70%	99.70%	99.70%
Anti-dilutive stock options excluded from EPS calculation
Income from discontinued operations attributable to common stockholders for basic and diluted earnings per share	$ 5.6	$ 5.2	$ 4.9	$ 8.3
Net income attributable to common stockholders for basic and diluted earnings per share	$ 300.8	$ 99.2	$ 493.9	$ 151.1
Anti-dilutive stock options excluded from earnings per share calculation (in shares)	0.2	0.0	0.2	0.3