Earnings Per Share (Computation of Basic and Diluted Earnings Per Share) (Details) - USD ($) $ / shares in Units, shares in Millions, $ in Millions	12 Months Ended
	Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2020
Earnings Per Share [Abstract]
Net income	$ 497.1	$ 464.0	$ 356.3
Net loss from discontinued operations	0.0	0.0	0.8
Income from continuing operations	$ 497.1	$ 464.0	$ 357.1
Weighted-average shares outstanding - basic (in shares)	35.7	37.2	38.3
Add: Potential effect of diluted securities attributable to stock-based payments	0.1	0.3	0.3
Weighted-average shares outstanding - diluted (in shares)	35.8	37.5	38.6
Earnings per share – Basic:
Income from continuing operations (in usd per share)	$ 13.92	$ 12.47	$ 9.32
Loss from discontinued operations (in usd per share)	0	0	(0.02)
Net income (in usd per share)	13.92	12.47	9.30
Earnings per share – Diluted:
Income from continuing operations (in usd per share)	13.88	12.39	9.26
Loss from discontinued operations (in usd per share)	0	0	(0.02)
Net income (in usd per share)	$ 13.88	$ 12.39	$ 9.24
Antidilutive securities excluded from computation of earnings per share, amount	0.3