Earnings Per Share (Computation Of Basic And Diluted Earnings Per Share) (Detail) - USD ($) $ / shares in Units, shares in Millions, $ in Millions	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Earnings Per Share [Abstract]
Net income attributable to common shareholders	$ 68.7	$ 63.1
Average basic shares outstanding	59.7	59.3
Effect of dilutive stock options	1.3	1.0
Average diluted shares outstanding	61.0	60.3
Earnings per share - basic:
Net income attributable to common shareholders	$ 1.15	$ 1.06
Earnings per share - diluted:
Net income attributable to common shareholders	$ 1.13	$ 1.05