Restructuring - Summary of Restructuring Activities (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended		30 Months Ended
	Jun. 30, 2026	Jun. 30, 2025	Jun. 30, 2026	Jun. 30, 2025	Jun. 30, 2026
Restructuring Cost and Reserve [Line Items]
Total impairment and restructuring	$ 215.8	$ 17.6	$ 223.6	$ 37.6	$ 292.4
Severance and employee benefits \| Stickney Shutdown
Restructuring Cost and Reserve [Line Items]
Total impairment and restructuring	2.0	0.0	2.0	0.0	2.0
Severance and employee benefits \| Phthalic Anhydride Shutdown
Restructuring Cost and Reserve [Line Items]
Total impairment and restructuring	0.0	0.5	0.1	0.6	1.1
Impairment \| Stickney Shutdown
Restructuring Cost and Reserve [Line Items]
Total impairment and restructuring	164.6	0.0	164.6	0.0	164.6
Depreciation and asset disposal costs \| Stickney Shutdown
Restructuring Cost and Reserve [Line Items]
Total impairment and restructuring	8.5	0.0	8.5	0.0	8.5
Depreciation and asset disposal costs \| Phthalic Anhydride Shutdown
Restructuring Cost and Reserve [Line Items]
Total impairment and restructuring	0.2	4.6	0.2	18.5	26.8
Plant cleaning, waste disposal and demolition costs \| Stickney Shutdown
Restructuring Cost and Reserve [Line Items]
Total impairment and restructuring	36.4	0.0	36.4	0.0	36.4
Plant cleaning, waste disposal and demolition costs \| Phthalic Anhydride Shutdown
Restructuring Cost and Reserve [Line Items]
Total impairment and restructuring	0.9	7.9	1.3	7.9	14.7
Workforce reduction program
Restructuring Cost and Reserve [Line Items]
Total impairment and restructuring	0.0	0.2	0.0	3.3	8.3
Consulting services
Restructuring Cost and Reserve [Line Items]
Total impairment and restructuring	2.7	4.4	5.1	7.3	21.0
Other restructuring costs
Restructuring Cost and Reserve [Line Items]
Total impairment and restructuring	$ 0.5	$ 0.0	$ 5.4	$ 0.0	$ 9.0