Earnings Per Share (Computation of Basic and Diluted Earnings Per Share) (Details) - USD ($) $ / shares in Units, shares in Millions, $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2022	Sep. 30, 2021	Sep. 30, 2022	Sep. 30, 2021
Earnings Per Share [Abstract]
Net income	$ 141.9	$ 126.3	$ 402.7	$ 380.4
Exclude: Income from discontinued operations	0.0	0.0	0.0	0.1
Income from continuing operations	$ 141.9	$ 126.3	$ 402.7	$ 380.5
Weighted average number of shares outstanding, basic (in shares)	35.4	36.8	35.8	37.4
Add: Potential effect of dilutive securities attributable to stock-based payments	0.1	0.2	0.1	0.3
Weighted-average shares outstanding – diluted	35.5	37.0	35.9	37.7
Earnings per share – Basic:
Income from continuing operations (in dollars per share)	$ 4.00	$ 3.43	$ 11.25	$ 10.17
Loss from discontinued operations (in dollars per share)	0	0	0	0
Net income (in dollars per share)	4.00	3.43	11.25	10.17
Earnings per share – Diluted:
Income from continuing operations (in dollars per share)	3.99	3.41	11.22	10.10
Loss from discontinued operations (in dollars per share)	0	0	0	0
Net income (in dollars per share)	$ 3.99	$ 3.41	$ 11.22	$ 10.10