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, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Earnings Per Share [Abstract]
Net income attributable to common shareholders	$ 68.2	$ 63.5	$ 200.5	$ 186.8
Average basic shares outstanding	59.5	58.5	59.4	58.3
Effect of dilutive stock options	0.9	0.9	1.0	0.9
Average diluted shares outstanding	60.4	59.4	60.4	59.2
Earnings per share - basic:
Net income attributable to common shareholders	$ 1.15	$ 1.09	$ 3.38	$ 3.20
Earnings per share - diluted:
Net income attributable to common shareholders	$ 1.13	$ 1.07	$ 3.32	$ 3.16