Segment financial information - product lines (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
Disaggregation by product line
Net sales	$ 1,785.6	$ 1,519.0
Proprietary materials & consumables
Disaggregation by product line
Net sales	565.2	478.5
Third party materials & consumables
Disaggregation by product line
Net sales	758.4	650.4
Services & specialty procurement
Disaggregation by product line
Net sales	219.8	191.1
Equipment & instrumentation
Disaggregation by product line
Net sales	$ 242.2	$ 199.0