Post Employment Plans - Net periodic pension cost (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Pension plan
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Service costs	$ 3.0	$ 4.5	$ 4.1
Interest cost	3.8	3.3	3.6
Expected return on assets	(5.3)	(4.3)	(3.9)
Curtailment	(1.2)	(0.7)	0.0
Net actuarial loss	0.6	0.8	0.5
Net periodic pension cost	0.9	3.6	4.3
Other Postretirement Benefits Plan
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Service costs	0.6	0.6	0.6
Interest cost	0.2	0.2	0.2
Expected return on assets	0.0	0.0	0.0
Curtailment	0.0	0.0	0.0
Net actuarial loss	(0.1)	(0.1)	0.0
Net periodic pension cost	$ 0.7	$ 0.7	$ 0.8