Stock-Based Compensation (Detail) - Stock-Based Compensation Expense By Award Type - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2015	Sep. 30, 2014
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Total stock-based compensation expense	$ 9.6	$ 8.8	$ 37.0	$ 29.4
Retirement eligible employees equity award
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Total stock-based compensation expense	3.0	2.9	17.4	12.7
Stock appreciation rights (SARs)
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Total stock-based compensation expense	1.1	1.0	4.5	3.9
Common stock equivalents (CSEs)
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Total stock-based compensation expense	0.2	0.2	0.5	0.5
Restricted stock units (RSUs)
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Total stock-based compensation expense	$ 8.3	$ 7.6	$ 32.0	$ 25.0