Income Taxes - Uncertain tax positions (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Movement in uncertain tax positions
Uncertain tax positions at the beginning of the period	$ 12.8	$ 13.1	$ 14.0
Gross increase - tax position in prior periods	0.2	0.2	0.2
Gross decrease - tax position in prior periods	(0.3)		(0.6)
Gross increase - current period tax position			0.1
Settlements	(7.8)
Foreign exchange	(1.5)	(0.5)	(0.6)
Uncertain tax positions at the end of the period	3.4	$ 12.8	$ 13.1
Interest and penalties included within uncertain tax positions	2.0
Impact of uncertain tax positions on effective tax rate, if recognized	$ 3.4