Disaggregation of sales - Schedule of Disaggregates of Net Sales of our Chemicals Segment (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2025	Dec. 31, 2024	Dec. 31, 2023
Disaggregation of Revenue [Line Items]
Net sales	$ 2,077.0	$ 2,104.8	$ 1,921.7
Point of Origin | Operating Segment
Disaggregation of Revenue [Line Items]
Net sales	2,077.0	2,104.8	1,921.7
Point of Origin | Operating Segment | United States
Disaggregation of Revenue [Line Items]
Net sales	1,390.4	1,396.1	1,284.4
Point of Origin | Operating Segment | Germany
Disaggregation of Revenue [Line Items]
Net sales	839.1	826.6	726.4
Point of Origin | Operating Segment | Canada
Disaggregation of Revenue [Line Items]
Net sales	289.3	351.5	351.0
Point of Origin | Operating Segment | Norway
Disaggregation of Revenue [Line Items]
Net sales	250.3	278.6	252.1
Point of Origin | Operating Segment | Belgium
Disaggregation of Revenue [Line Items]
Net sales	236.7	237.8	217.1
Point of Origin | Eliminations
Disaggregation of Revenue [Line Items]
Net sales	(928.8)	(985.8)	(909.3)
Point of Destination | Operating Segment
Disaggregation of Revenue [Line Items]
Net sales	2,077.0	2,104.8	1,921.7
Point of Destination | Operating Segment | Europe
Disaggregation of Revenue [Line Items]
Net sales	861.8	842.2	738.5
Point of Destination | Operating Segment | North America
Disaggregation of Revenue [Line Items]
Net sales	929.0	914.0	871.0
Chemicals
Disaggregation of Revenue [Line Items]
Net sales	1,859.4	1,887.1	1,666.5
Chemicals | Point of Origin | Operating Segment
Disaggregation of Revenue [Line Items]
Net sales	1,859.4	1,887.1	1,666.5
Chemicals | Point of Origin | Operating Segment | United States
Disaggregation of Revenue [Line Items]
Net sales	1,172.9	1,178.4	1,029.2
Chemicals | Point of Origin | Operating Segment | Germany
Disaggregation of Revenue [Line Items]
Net sales	839.1	826.6	726.4
Chemicals | Point of Origin | Operating Segment | Canada
Disaggregation of Revenue [Line Items]
Net sales	289.3	351.5	351.0
Chemicals | Point of Origin | Operating Segment | Norway
Disaggregation of Revenue [Line Items]
Net sales	250.3	278.6	252.1
Chemicals | Point of Origin | Operating Segment | Belgium
Disaggregation of Revenue [Line Items]
Net sales	236.7	237.8	217.1
Chemicals | Point of Origin | Eliminations
Disaggregation of Revenue [Line Items]
Net sales	(928.9)	(985.8)	(909.3)
Chemicals | Point of Destination | Operating Segment
Disaggregation of Revenue [Line Items]
Net sales	1,859.4	1,887.1	1,666.5
Chemicals | Point of Destination | Operating Segment | Europe
Disaggregation of Revenue [Line Items]
Net sales	861.0	841.5	737.8
Chemicals | Point of Destination | Operating Segment | North America
Disaggregation of Revenue [Line Items]
Net sales	713.3	698.3	618.1
Chemicals | Point of Destination | Operating Segment | Other
Disaggregation of Revenue [Line Items]
Net sales	$ 285.1	$ 347.3	$ 310.6