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, 2020	Jun. 30, 2020	Mar. 31, 2020	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Sep. 30, 2020	Sep. 30, 2019
Earnings Per Share [Abstract]
Net income attributable to common shareholders	$ 56.6			$ 72.5			$ 134.2	$ 245.9
Net income before allocation to noncontrolling interests	$ 56.6	$ 14.8	$ 62.8	$ 72.6	$ 91.0	$ 82.5	$ 134.2	$ 246.1
Average basic shares outstanding	58.1			60.0			58.4	59.9
Effect of dilutive stock options	0.4			0.8			0.5	0.9
Average diluted shares outstanding	58.5			60.8			58.9	60.8
Earnings per share - basic:
Net income attributable to common shareholders	$ 0.97			$ 1.21			$ 2.30	$ 4.11
Earnings per share - diluted:
Net income attributable to common shareholders	$ 0.97			$ 1.19			$ 2.28	$ 4.05