Earnings Per Share (Details) - USD ($) $ / shares in Units, shares in Millions, $ in Millions	3 Months Ended								12 Months Ended
	Dec. 31, 2023	Sep. 30, 2023	Jun. 30, 2023	Mar. 31, 2023	Dec. 31, 2022	Sep. 30, 2022	Jun. 30, 2022	Mar. 31, 2022	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Net Income (Loss) Attributable to Parent [Abstract]
Income from continuing operations	$ 191.7	$ 216.9	$ 226.7	$ 83.6	$ 153.0	$ 233.3	$ 280.7	$ 191.0	$ 718.9	$ 858.0	$ 385.6
Less: dividends declared									160.5	134.6	112.7
Undistributed earnings									$ 558.4	$ 723.4	$ 272.9
Percent allocated to common stockholders									99.80%	99.80%	99.70%
Undistributed earnings available to common shareholders									$ 557.1	$ 721.8	$ 272.1
Add: dividends declared to common shares, restricted share units and vested and deferred restricted and performance shares									160.2	134.3	112.4
Income from continuing operations attributable to common stockholders									$ 717.3	$ 856.1	$ 384.5
Shares:
Basic weighted-average shares outstanding (in shares)									49.9	51.8	52.5
Effect of dilutive securities:
Performance awards (in shares)									0.1	0.2	0.2
Stock options (in shares)									0.4	0.5	0.5
Diluted weighted-average shares outstanding (in shares)									50.4	52.5	53.2
Per share income from continuing operations attributable to common shares:
Basic (in dollars per share)	$ 3.96	$ 4.37	$ 4.46	$ 1.63	$ 2.97	$ 4.49	$ 5.41	$ 3.66	$ 14.38	$ 16.53	$ 7.33
Diluted (in dollars per share)	$ 3.91	$ 4.32	$ 4.42	$ 1.61	$ 2.93	$ 4.42	$ 5.33	$ 3.61	$ 14.22	$ 16.30	$ 7.23
Basic weighted-average shares outstanding (in shares)									49.9	51.8	52.5
Basic weighted-average shares outstanding and unvested restricted shares expected to vest (in shares)									50.0	51.9	52.6
Percent allocated to common stockholders									99.80%	99.80%	99.70%
Anti-dilutive stock options excluded from EPS calculation
Income from discontinued operations attributable to common stockholders for basic earnings per share									$ 48.5	$ 65.8	$ 36.0
Income from discontinued operations attributable to common stockholders for dilutive earnings per share									48.5	65.8	36.0
Net income attributable to common stockholders for basic earnings per share									765.6	921.8	420.5
Net income attributable to common stockholders for diluted earnings per share									$ 765.6	$ 921.8	$ 420.5
Antidilutive stock options excluded from earnings per share calculation (in shares)									0.6	0.2	0.1