Earnings Per Share (Computation Of Basic And Diluted Earnings Per Share) (Detail) - USD ($) $ / shares in Units, shares in Millions, $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Earnings Per Share [Abstract]
Net income from continuing operations attributable to common shareholders	$ 111.4	$ 49.4	$ 325.5	$ 120.3
Net income from continuing operations attributable to common shareholders	5.2	7.2	37.8	13.9
Net income attributable to common shareholders	$ 116.6	$ 56.6	$ 363.3	$ 134.2
Average basic shares outstanding (in shares)	58.7	58.1	58.5	58.4
Effect of dilutive stock options	0.8	0.4	0.7	0.5
Average diluted shares outstanding (in shares)	59.5	58.5	59.2	58.9
Earnings per share - basic:
Earnings per basic share from continuing operations (in dollars per share)	$ 1.90	$ 0.85	$ 5.56	$ 2.06
Earnings per basic share from discontinued operations (in dollars per share)	0.09	0.12	0.65	0.24
Earnings per basic share (in dollars per share)	1.99	0.97	6.21	2.30
Earnings per share - diluted:
Earnings per diluted share from continuing operations (in dollars per share)	1.87	0.84	5.50	2.04
Earnings per diluted share from discontinued operations (in dollars per share)	0.09	0.13	0.64	0.24
Earnings per diluted share (in dollars per share)	$ 1.96	$ 0.97	$ 6.14	$ 2.28