Stockholders' Equity - Total Share-based Compensation Expense (Detail) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Total share-based incentive compensation expense	$ 16.9	$ 25.0	$ 30.6
Associated tax benefits recognized	6.2	9.3	11.3
2012 Three-year PSU Awards [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Total share-based incentive compensation expense	1.9
2011 Three-year PSU Awards [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Total share-based incentive compensation expense	1.7	3.0
2010 Three-year PSU Awards [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Total share-based incentive compensation expense	0.9	6.0	3.0
2009 Two-year PSU Awards [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Total share-based incentive compensation expense		(0.7)	10.4
2009 Three-year PSU Awards [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Total share-based incentive compensation expense		7.4	7.0
2012 President & COO Four-year Incentive Compensation [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Total share-based incentive compensation expense	0.2
SLO Awards [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Total share-based incentive compensation expense	0.7	0.3	1.0
Other long-term share-based incentive compensation programs [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Total share-based incentive compensation expense	$ 11.5	$ 9.0	$ 9.2