Total Share-based Compensation Expense (Detail) (USD $) In Millions, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2012	Sep. 30, 2011	Sep. 30, 2012	Sep. 30, 2011
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Total share-based incentive compensation expense	$ 6.6	$ 4.5	$ 16.9	$ 17.7
2012 Three-year PSU Awards [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Total share-based incentive compensation expense	0.8		2.2
2011 Three-year PSU Awards [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Total share-based incentive compensation expense	0.6	0.7	1.4	2.5
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	0.8	1.2	4.6
2009 Three-year PSU Awards [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Total share-based incentive compensation expense		1.2		3.6
2012 CEO Incentive Compensation [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Total share-based incentive compensation expense	1.1		3.4
SLO Awards [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Total share-based incentive compensation expense	0.2	(0.3)	0.6	0.3
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	$ 3.0	$ 2.1	$ 8.1	$ 6.7