Reconciliation of unrecognized tax benefits (Detail) (USD $) In Millions, unless otherwise specified	3 Months Ended
	Mar. 31, 2012	Mar. 31, 2011
Significant Change in Unrecognized Tax Benefits is Reasonably Possible [Line Items]
Beginning Balance	$ 19.5	$ 26.3
Unrecognized Tax Benefits Increases Resulting From Current Period Tax Positions	0.7	2.2
Unrecognized Tax Benefits Increases Resulting From Prior Period Tax Positions	0	0
Reduction as a result of lapse of statute of limitations	0	0
Unrecognized Tax Benefits Decreases Resulting From Prior Period Tax Positions	0	0
Unrecognized Tax Benefits Decreases Resulting From Settlements With Taxing Authorities	0	(4.4)
Ending Balance	$ 20.2	$ 24.1