Pension plans 5 (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Defined Benefit Plan Disclosure [Line Items]
Settlement loss (gain)		$ (10.6)	$ (6.1)
Equity Securities [Member]
Defined Benefit Plan Disclosure [Line Items]
Target asset allocation (as a percent)	31.00%
Debt Securities [Member]
Defined Benefit Plan Disclosure [Line Items]
Target asset allocation (as a percent)	69.00%
Pension Plans, Defined Benefit [Member]
Defined Benefit Plan Disclosure [Line Items]
Settlement loss (gain)	$ 0.0	$ (10.6)
Domestic Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Expected return on plan assets	6.75%	7.25%	7.50%
2018	$ 38.4
2019	38.8
2020	43.0
2021	40.3
2022	40.2
Years 2023 - 2027	$ 202.2
Weighted-average discount rate	4.25%	3.75%
Foreign Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Expected return on plan assets	5.27%	5.30%	6.08%
2018	$ 1.6
2019	1.6
2020	2.2
2021	2.1
2022	2.2
Years 2023 - 2027	$ 12.0
Weighted-average discount rate	3.33%	2.80%