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, 2016	Sep. 30, 2015	Sep. 30, 2016	Sep. 30, 2015
Earnings Per Share [Abstract]
Net income attributable to common shareholders	$ 63.5	$ 56.9	$ 186.8	$ 163.7
Average basic shares outstanding	58.5	58.1	58.3	58.0
Effect of dilutive stock options	0.9	0.7	0.9	0.8
Average diluted shares outstanding	59.4	58.8	59.2	58.8
Earnings per share - basic:
Net income attributable to common shareholders	$ 1.09	$ 0.98	$ 3.20	$ 2.82
Earnings per share - diluted:
Net income attributable to common shareholders	$ 1.07	$ 0.97	$ 3.16	$ 2.78