Stockholders' Equity - Estimated Amount of Total Share-based Compensation Expense (Detail) (USD $) In Millions, unless otherwise specified	Dec. 31, 2012
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
2013	$ 15.7
2014	9.2
2015	2.8
Total	27.7
2012 Three-year PSU Awards [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
2013	2.2
2014	2.2
2015
Total	4.4
2012 President & COO Four-year Incentive Compensation [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
2013	0.6
2014	0.4
2015	0.3
Total	1.3
2011 Three-year PSU Awards [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
2013	2.3
2014
2015
Total	2.3
SLO Awards [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
2013	0.2
2014
2015
Total	0.2
Other long-term share-based incentive compensation programs [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
2013	10.4
2014	6.6
2015	2.5
Total	$ 19.5