Revenue - disaggregation of sales - Schedule of Disaggregates of Net Sales of our Chemicals Segment (Detail) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2025	Jun. 30, 2024	Jun. 30, 2025	Jun. 30, 2024
Revenue - disaggregation of sales [Line Items]
Net sales	$ 540.4	$ 559.7	$ 1,079.0	$ 1,090.3
Chemicals
Revenue - disaggregation of sales [Line Items]
Net sales	494.4	500.5	984.2	979.3
Point of Origin | Chemicals
Revenue - disaggregation of sales [Line Items]
Net sales	494.4	500.5	984.2	979.3
Point of Origin | Chemicals | Eliminations
Revenue - disaggregation of sales [Line Items]
Net sales	(189.9)	(231.7)	(486.3)	(435.9)
Point of Origin | Chemicals | Operating Segment | United States
Revenue - disaggregation of sales [Line Items]
Net sales	275.7	279.7	598.1	520.6
Point of Origin | Chemicals | Operating Segment | Germany
Revenue - disaggregation of sales [Line Items]
Net sales	214.5	216.2	431.3	428.4
Point of Origin | Chemicals | Operating Segment | Canada
Revenue - disaggregation of sales [Line Items]
Net sales	55.7	97.6	166.5	186.9
Point of Origin | Chemicals | Operating Segment | Norway
Revenue - disaggregation of sales [Line Items]
Net sales	72.8	77.7	143.3	148.7
Point of Origin | Chemicals | Operating Segment | Belgium
Revenue - disaggregation of sales [Line Items]
Net sales	65.6	61.0	131.3	130.6
Point of Destination | Chemicals
Revenue - disaggregation of sales [Line Items]
Net sales	494.4	500.5	984.2	979.3
Point of Destination | Chemicals | Operating Segment | Europe
Revenue - disaggregation of sales [Line Items]
Net sales	226.8	222.6	455.3	437.5
Point of Destination | Chemicals | Operating Segment | North America
Revenue - disaggregation of sales [Line Items]
Net sales	188.2	182.5	378.4	348.5
Point of Destination | Chemicals | Operating Segment | Other
Revenue - disaggregation of sales [Line Items]
Net sales	$ 79.4	$ 95.4	$ 150.5	$ 193.3