Earnings Per Share (Computation Of Basic And Diluted Earnings Per Share) (Detail) - USD ($) $ / shares in Units, shares in Millions, $ in Millions	3 Months Ended				6 Months Ended
	Jun. 30, 2020	Mar. 31, 2020	Jun. 30, 2019	Mar. 31, 2019	Jun. 30, 2020	Jun. 30, 2019
Earnings Per Share [Abstract]
Net income attributable to common shareholders	$ 14.8	$ 62.8	$ 91.0		$ 77.6	$ 173.4
Net income before allocation to noncontrolling interests	$ 14.8	$ 62.8	$ 91.0	$ 82.5	$ 77.6	$ 173.5
Average basic shares outstanding	58.0		59.9		58.5	59.8
Effect of dilutive stock options	0.5		0.9		0.6	1.0
Average diluted shares outstanding	58.5		60.8		59.1	60.8
Earnings per share - basic:
Net income attributable to common shareholders	$ 0.26		$ 1.52		$ 1.33	$ 2.90
Earnings per share - diluted:
Net income attributable to common shareholders	$ 0.25		$ 1.50		$ 1.31	$ 2.85