Note Income taxes (Reconciliation of unrecognized tax benefits) (Detail) - USD ($) $ in Millions	3 Months Ended
	Jun. 30, 2018	Mar. 31, 2018	Jun. 30, 2017	Mar. 31, 2017
Income Tax Disclosure
Beginning Balance	$ 7.5	$ 7.3	$ 7.6	$ 7.4
Addition for tax positions	0.3	0.2	0.3	0.2
Reduction as a result of settlements	0.0		(0.3)
Ending Balance	$ 7.8	$ 7.5	$ 7.6	$ 7.6