Stock-Based Compensation (Detail) - Stock-Based Compensation Expense By Award Type (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2014		Dec. 31, 2013		Dec. 31, 2012
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock-based compensation expense	$ 38.8	[1]	$ 34.7	[1]	$ 36.4	[1]
Stock appreciation rights
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock-based compensation expense	5.0		5.2		6.4
Common stock equivalents
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock-based compensation expense	0.6		0.6		0.5
Restricted stock units
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock-based compensation expense	$ 33.2		$ 28.9		$ 29.5

[1] Includes charges of $14.8 million, $12.5 million, and $5.1 million in 2014, 2013 and 2012, respectively, for awards to retirement-eligible employees since these awards vest on an accelerated basis