Stock-Based Compensation (Detail) - Stock-Based Compensation Expense By Award Type - USD ($) $ in Millions		3 Months Ended		6 Months Ended
		Jun. 30, 2015	Jun. 30, 2014	Jun. 30, 2015	Jun. 30, 2014
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Total stock-based compensation expense	[1]	$ 10.7	$ 6.9	$ 27.4	$ 20.6
Retirement eligible employees equity award
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Total stock-based compensation expense		3.9	2.1	14.4	9.8
Stock appreciation rights (SARs)
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Total stock-based compensation expense		1.2	1.0	3.4	2.9
Common stock equivalents (CSEs)
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Total stock-based compensation expense		0.2	0.2	0.3	0.3
Restricted stock units (RSUs)
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Total stock-based compensation expense		$ 9.3	$ 5.7	$ 23.7	$ 17.4

[1] Includes charges of $3.9 million and $2.1 million for the three months ended June 30, 2015 and 2014, respectively, and $14.4 million and $9.8 million for the six months ended June 30, 2015 and 2014, respectively, for awards to retirement-eligible employees since these awards vest on an accelerated basis.