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	3 Months Ended								12 Months Ended
	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Accounting Policies [Abstract]
Antidilutive Securities Excluded from Computation of Earnings Per Share, Amount									1.2	0.4	0.4
Less: Noncontrolling interest in subsidiaries’ earnings (loss)									$ 0.3	$ (0.1)	$ 0.7
Net income attributable to common shareholders	$ (112.6)	$ 72.5	$ 91.0	$ 82.4					$ 133.3	$ 335.6	$ 171.8
Weighted average basic shares outstanding (in shares)									59.8	59.6	59.4
Effect of dilutive stock options									0.8	1.4	1.0
Average diluted shares outstanding									60.6	61.0	60.4
Earnings per share - basic:
Basic earnings per share (in dollars per share)	$ (1.89)	$ 1.21	$ 1.52	$ 1.38	$ 1.51	$ 1.62	$ 1.35	$ 1.15	$ 2.23	$ 5.63	$ 2.89
Earnings per share - diluted:
Diluted earnings per share (in dollars per share)	$ (1.89)	$ 1.19	$ 1.50	$ 1.36	$ 1.46	$ 1.59	$ 1.32	$ 1.13	$ 2.20	$ 5.50	$ 2.84