Nature of Operations and Significant Accounting Policies (Schedule of Earnings Per Share) (Details) - USD ($) $ / shares in Units, shares in Millions, $ in Millions	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Accounting Policies [Abstract]
Net income attributable to common shareholders	$ 188.3	$ 204.9	$ 178.0
Average basic shares outstanding (in shares)	56.8	56.7	56.7
Effect of dilutive share-based awards (in shares)	0.7	0.0	0.0
Average diluted shares outstanding (in shares)	57.5	56.7	56.7
Basic earnings per share (in dollars per share)	$ 3.31	$ 3.61	$ 3.14
Diluted earnings per share (in dollars per share)	$ 3.28	$ 3.61	$ 3.14