Nature of Operations and Significant Accounting Policies (Computation Of Basic And Diluted Earnings Per Share) (Details) - USD ($) $ / shares in Units, shares in Millions, $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Accounting Policies [Abstract]
Antidilutive Securities Excluded from Computation of Earnings Per Share, Amount	2.1	1.2	0.4
Less: Noncontrolling interest in subsidiaries’ earnings (loss)	$ 0.1	$ 0.3	$ (0.1)
Net income attributable to common shareholders	$ 181.0	$ 133.3	$ 335.6
Weighted average basic shares outstanding (in shares)	58.3	59.8	59.6
Effect of dilutive stock options	0.5	0.8	1.4
Average diluted shares outstanding	58.8	60.6	61.0
Earnings per share - basic:
Basic earnings per share (in dollars per share)	$ 3.10	$ 2.23	$ 5.63
Earnings per share - diluted:
Diluted earnings per share (in dollars per share)	$ 3.08	$ 2.20	$ 5.50