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, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Earnings Per Share [Abstract]
Net income attributable to common shareholders	$ 80.7	$ 69.2	$ 149.4	$ 132.3
Average basic shares outstanding	59.7	59.5	59.7	59.4
Effect of dilutive stock options	1.4	1.0	1.3	1.0
Average diluted shares outstanding	61.1	60.5	61.0	60.4
Earnings per share - basic:
Net income attributable to common shareholders	$ 1.35	$ 1.16	$ 2.50	$ 2.23
Earnings per share - diluted:
Net income attributable to common shareholders	$ 1.32	$ 1.14	$ 2.45	$ 2.19