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, 2026	Jun. 30, 2025	Jun. 30, 2026	Jun. 30, 2025
Revenue - disaggregation of sales
Net sales	$ 606.1	$ 540.4	$ 1,166.2	$ 1,079.0
Chemicals
Revenue - disaggregation of sales
Net sales	558.1	494.4	1,067.9	984.2
Point of Origin \| Chemicals
Revenue - disaggregation of sales
Net sales	558.1	494.4	1,067.9	984.2
Point of Origin \| Chemicals \| Eliminations
Revenue - disaggregation of sales
Net sales	(357.0)	(189.9)	(649.7)	(486.3)
Point of Origin \| Chemicals \| Operating Segment \| United States
Revenue - disaggregation of sales
Net sales	440.7	275.7	798.4	598.1
Point of Origin \| Chemicals \| Operating Segment \| Germany
Revenue - disaggregation of sales
Net sales	253.7	214.5	480.3	431.3
Point of Origin \| Chemicals \| Operating Segment \| Canada
Revenue - disaggregation of sales
Net sales	87.6	55.7	175.5	166.5
Point of Origin \| Chemicals \| Operating Segment \| Belgium
Revenue - disaggregation of sales
Net sales	70.3	65.6	134.5	131.3
Point of Origin \| Chemicals \| Operating Segment \| Norway
Revenue - disaggregation of sales
Net sales	62.8	72.8	128.9	143.3
Point of Destination \| Chemicals
Revenue - disaggregation of sales
Net sales	558.1	494.4	1,067.9	984.2
Point of Destination \| Chemicals \| Operating Segment \| Europe
Revenue - disaggregation of sales
Net sales	285.5	226.8	528.6	455.3
Point of Destination \| Chemicals \| Operating Segment \| North America
Revenue - disaggregation of sales
Net sales	199.0	188.2	385.2	378.4
Point of Destination \| Chemicals \| Operating Segment \| Other
Revenue - disaggregation of sales
Net sales	$ 73.6	$ 79.4	$ 154.1	$ 150.5