Disaggregation of sales - Schedule of Disaggregates of Net Sales of our Chemicals Segment (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Disaggregation Of Revenue [Line Items]
Net sales	$ 1,921.7	$ 2,222.5	$ 2,296.4
Point Of Origin | Operating Segment
Disaggregation Of Revenue [Line Items]
Net sales	1,921.7	2,222.5	2,296.4
Point Of Origin | Operating Segment | United States
Disaggregation Of Revenue [Line Items]
Net sales	1,284.4	1,518.9	1,409.1
Point Of Origin | Operating Segment | Germany
Disaggregation Of Revenue [Line Items]
Net sales	726.4	895.4	971.7
Point Of Origin | Operating Segment | Canada
Disaggregation Of Revenue [Line Items]
Net sales	351.0	389.4	371.9
Point Of Origin | Operating Segment | Belgium
Disaggregation Of Revenue [Line Items]
Net sales	217.1	306.5	295.7
Point Of Origin | Operating Segment | Norway
Disaggregation Of Revenue [Line Items]
Net sales	252.1	273.5	257.2
Point Of Origin | Eliminations
Disaggregation Of Revenue [Line Items]
Net sales	(909.3)	(1,161.2)	(1,009.2)
Point Of Destination | Operating Segment
Disaggregation Of Revenue [Line Items]
Net sales	1,921.7	2,222.5	2,296.4
Point Of Destination | Operating Segment | Europe
Disaggregation Of Revenue [Line Items]
Net sales	738.5	879.0	945.7
Point Of Destination | Operating Segment | North America
Disaggregation Of Revenue [Line Items]
Net sales	871.0	985.4	999.7
Chemicals
Disaggregation Of Revenue [Line Items]
Net sales	1,666.5	1,930.2	1,939.4
Chemicals | Point Of Origin | Operating Segment
Disaggregation Of Revenue [Line Items]
Net sales	1,666.5	1,930.2	1,939.4
Chemicals | Point Of Origin | Operating Segment | United States
Disaggregation Of Revenue [Line Items]
Net sales	1,029.2	1,226.6	1,052.1
Chemicals | Point Of Origin | Operating Segment | Germany
Disaggregation Of Revenue [Line Items]
Net sales	726.4	895.4	971.7
Chemicals | Point Of Origin | Operating Segment | Canada
Disaggregation Of Revenue [Line Items]
Net sales	351.0	389.4	371.9
Chemicals | Point Of Origin | Operating Segment | Belgium
Disaggregation Of Revenue [Line Items]
Net sales	217.1	306.5	295.7
Chemicals | Point Of Origin | Operating Segment | Norway
Disaggregation Of Revenue [Line Items]
Net sales	252.1	273.5	257.2
Chemicals | Point Of Origin | Eliminations
Disaggregation Of Revenue [Line Items]
Net sales	(909.3)	(1,161.2)	(1,009.2)
Chemicals | Point Of Destination | Operating Segment
Disaggregation Of Revenue [Line Items]
Net sales	1,666.5	1,930.2	1,939.4
Chemicals | Point Of Destination | Operating Segment | Europe
Disaggregation Of Revenue [Line Items]
Net sales	737.8	878.3	945.0
Chemicals | Point Of Destination | Operating Segment | North America
Disaggregation Of Revenue [Line Items]
Net sales	618.1	695.7	645.7
Chemicals | Point Of Destination | Operating Segment | Other
Disaggregation Of Revenue [Line Items]
Net sales	$ 310.6	$ 356.2	$ 348.7