Reconciliation of unrecognized tax benefits (Detail) (USD $) In Millions, unless otherwise specified	3 Months Ended
	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Sep. 30, 2013	Jun. 30, 2013	Mar. 31, 2013
Significant Change in Unrecognized Tax Benefits is Reasonably Possible [Line Items]
Beginning Balance	$ 10.3	$ 10.1	$ 9.8	$ 13.9	$ 13.6	$ 13.4
Unrecognized Tax Benefits Increases Resulting From Current Period Tax Positions	0.3	0.2	0.3	0.3	0.3	0.2
Unrecognized Tax Benefits Increases Resulting From Prior Period Tax Positions	0	0		0	0
Reduction as a result of lapse of statute of limitations	(2.5)			(5.7)
Unrecognized Tax Benefits, Decreases Resulting from Current Period Tax Positions	0	0	0	0	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	0	0	0	0	0
Ending Balance	$ 8.1	$ 10.3	$ 10.1	$ 8.5	$ 13.9	$ 13.6