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, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Earnings Per Share [Abstract]
Net income attributable to common shareholders	$ 97.0	$ 68.2	$ 246.4	$ 200.5
Average basic shares outstanding	59.7	59.5	59.7	59.4
Effect of dilutive stock options	1.4	0.9	1.4	1.0
Average diluted shares outstanding	61.1	60.4	61.1	60.4
Earnings per share - basic:
Net income attributable to common shareholders	$ 1.62	$ 1.15	$ 4.13	$ 3.38
Earnings per share - diluted:
Net income attributable to common shareholders	$ 1.59	$ 1.13	$ 4.04	$ 3.32