Disaggregation of sales - Schedule of Disaggregates of Net Sales of our Chemicals Segment (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2024	Dec. 31, 2023	Dec. 31, 2022
Disaggregation Of Revenue [Line Items]
Net sales	$ 2,104.8	$ 1,921.7	$ 2,222.5
Point of Origin | Operating Segment
Disaggregation Of Revenue [Line Items]
Net sales	2,104.8	1,921.7	2,222.5
Point of Origin | Operating Segment | United States
Disaggregation Of Revenue [Line Items]
Net sales	1,396.1	1,284.4	1,518.9
Point of Origin | Operating Segment | Germany
Disaggregation Of Revenue [Line Items]
Net sales	826.6	726.4	895.4
Point of Origin | Operating Segment | Canada
Disaggregation Of Revenue [Line Items]
Net sales	351.5	351.0	389.4
Point of Origin | Operating Segment | Norway
Disaggregation Of Revenue [Line Items]
Net sales	278.6	252.1	273.5
Point of Origin | Operating Segment | Belgium
Disaggregation Of Revenue [Line Items]
Net sales	237.8	217.1	306.5
Point of Origin | Eliminations
Disaggregation Of Revenue [Line Items]
Net sales	(985.8)	(909.3)	(1,161.2)
Point of Destination | Operating Segment
Disaggregation Of Revenue [Line Items]
Net sales	2,104.8	1,921.7	2,222.5
Point of Destination | Operating Segment | Europe
Disaggregation Of Revenue [Line Items]
Net sales	842.2	738.5	879.0
Point of Destination | Operating Segment | North America
Disaggregation Of Revenue [Line Items]
Net sales	914.0	871.0	985.4
Chemicals
Disaggregation Of Revenue [Line Items]
Net sales	1,887.1	1,666.5	1,930.2
Chemicals | Point of Origin | Operating Segment
Disaggregation Of Revenue [Line Items]
Net sales	1,887.1	1,666.5	1,930.2
Chemicals | Point of Origin | Operating Segment | United States
Disaggregation Of Revenue [Line Items]
Net sales	1,178.4	1,029.2	1,226.6
Chemicals | Point of Origin | Operating Segment | Germany
Disaggregation Of Revenue [Line Items]
Net sales	826.6	726.4	895.4
Chemicals | Point of Origin | Operating Segment | Canada
Disaggregation Of Revenue [Line Items]
Net sales	351.5	351.0	389.4
Chemicals | Point of Origin | Operating Segment | Norway
Disaggregation Of Revenue [Line Items]
Net sales	278.6	252.1	273.5
Chemicals | Point of Origin | Operating Segment | Belgium
Disaggregation Of Revenue [Line Items]
Net sales	237.8	217.1	306.5
Chemicals | Point of Origin | Eliminations
Disaggregation Of Revenue [Line Items]
Net sales	(985.8)	(909.3)	(1,161.2)
Chemicals | Point of Destination | Operating Segment
Disaggregation Of Revenue [Line Items]
Net sales	1,887.1	1,666.5	1,930.2
Chemicals | Point of Destination | Operating Segment | Europe
Disaggregation Of Revenue [Line Items]
Net sales	841.5	737.8	878.3
Chemicals | Point of Destination | Operating Segment | North America
Disaggregation Of Revenue [Line Items]
Net sales	698.3	618.1	695.7
Chemicals | Point of Destination | Operating Segment | Other
Disaggregation Of Revenue [Line Items]
Net sales	$ 347.3	$ 310.6	$ 356.2