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, 2021	Sep. 30, 2021	Jun. 30, 2021	Mar. 31, 2021	Dec. 31, 2020	Sep. 30, 2020	Jun. 30, 2020	Mar. 31, 2020	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Accounting Policies [Abstract]
Net income from continuing operations attributable to common shareholders	$ 68.8	$ 111.4	$ 110.7	$ 103.4	$ 42.6	$ 49.4	$ 13.4	$ 57.7	$ 394.3	$ 163.1	$ 112.3
Income from discontinued operations, net of tax	3.3	5.2	27.6	5.0	4.3	7.2	1.4	5.0	41.1	17.9	21.0
Net income attributable to common shareholders	$ 72.1	$ 116.6	$ 138.3	$ 108.4	$ 46.9	$ 56.6	$ 14.8	$ 62.7	$ 435.4	$ 181.0	$ 133.3
Average basic shares outstanding (in shares)									58.4	58.3	59.8
Effect of dilutive share-based awards (in shares)									0.8	0.5	0.8
Average diluted shares outstanding (in shares)									59.2	58.8	60.6
Earnings per basic share:
Earnings per basic share from continuing operations (in dollars per share)	$ 1.19	$ 1.90	$ 1.89	$ 1.78	$ 0.73	$ 0.85	$ 0.23	$ 0.98	$ 6.76	$ 2.79	$ 1.88
Earnings per basic share from discontinued operations (in dollars per share)	0.06	0.09	0.47	0.08	0.07	0.12	0.03	0.09	0.70	0.31	0.35
Basic earnings per share (in dollars per share)	1.25	1.99	2.36	1.86	0.80	0.97	0.26	1.07	7.46	3.10	2.23
Earnings per diluted share:
Earnings per diluted share from continuing operations (in dollars per share)	1.16	1.87	1.87	1.76	0.73	0.84	0.23	0.96	6.66	2.77	1.85
Earnings per diluted share from discontinued operations (in dollars per share)	0.06	0.09	0.46	0.08	0.07	0.13	0.02	0.09	0.70	0.31	0.35
Diluted earnings per share (in dollars per share)	$ 1.22	$ 1.96	$ 2.33	$ 1.84	$ 0.80	$ 0.97	$ 0.25	$ 1.05	$ 7.36	$ 3.08	$ 2.20