Reconciliation of unrecognized tax benefits (Detail) (USD $) In Millions, unless otherwise specified	3 Months Ended
	Jun. 30, 2012	Mar. 31, 2012	Jun. 30, 2011	Mar. 31, 2011
Significant Change in Unrecognized Tax Benefits is Reasonably Possible [Line Items]
Beginning Balance	$ 20.2	$ 19.5	$ 24.1	$ 26.3
Unrecognized Tax Benefits Increases Resulting From Current Period Tax Positions	0	0.7	0.8	2.2
Unrecognized Tax Benefits Increases Resulting From Prior Period Tax Positions	0		2.1
Reduction as a result of lapse of statute of limitations		0		0
Unrecognized Tax Benefits, Decreases Resulting from Current Period Tax Positions	(0.2)		0
Unrecognized Tax Benefits Decreases Resulting From Prior Period Tax Positions	(0.7)		0
Unrecognized Tax Benefits Decreases Resulting From Settlements With Taxing Authorities	0	0	0	(4.4)
Ending Balance	$ 19.3	$ 20.2	$ 27.0	$ 24.1