RESTRUCTURING CHARGES (Details 3) - USD ($) $ in Millions	3 Months Ended						9 Months Ended		64 Months Ended
RESTRUCTURING CHARGES (Details 3) - USD ($) $ in Millions	Sep. 30, 2026	Jun. 30, 2026	Mar. 31, 2026	Sep. 30, 2025	Jun. 30, 2025	Mar. 31, 2025	Sep. 30, 2026	Sep. 30, 2025	Jun. 30, 2026
Restructuring Cost and Reserve [Line Items]
Restructuring charges	$ 1.7	$ 10.5	$ 9.1	$ 2.9	$ 7.4	$ 4.0	$ 21.3	$ 14.3	$ 281.2
Write-off of equipment and facility
Restructuring Cost and Reserve [Line Items]
Restructuring charges	0.0	1.6	0.8	0.0	0.0	0.0			86.5
Employee severance and related benefit costs
Restructuring Cost and Reserve [Line Items]
Restructuring charges	0.0	0.0	4.1	0.6	3.8	1.6			36.2
Facility exit costs
Restructuring Cost and Reserve [Line Items]
Restructuring charges	1.5	8.9	4.1	2.3	3.6	2.2			113.1
Lease and other contract termination costs
Restructuring Cost and Reserve [Line Items]
Restructuring charges	0.2	$ 0.0	$ 0.1	0.0	$ 0.0	$ 0.2			45.4
Chlor Alkali Products and Vinyls
Restructuring Cost and Reserve [Line Items]
Restructuring charges	0.0			0.0			0.0	0.0	155.3
Chlor Alkali Products and Vinyls \| Write-off of equipment and facility
Restructuring Cost and Reserve [Line Items]
Restructuring charges									61.6
Chlor Alkali Products and Vinyls \| Employee severance and related benefit costs
Restructuring Cost and Reserve [Line Items]
Restructuring charges									12.5
Chlor Alkali Products and Vinyls \| Facility exit costs
Restructuring Cost and Reserve [Line Items]
Restructuring charges									74.3
Chlor Alkali Products and Vinyls \| Lease and other contract termination costs
Restructuring Cost and Reserve [Line Items]
Restructuring charges									6.9
Epoxy
Restructuring Cost and Reserve [Line Items]
Restructuring charges	0.0			0.0			0.0	0.0	122.8
Epoxy \| Write-off of equipment and facility
Restructuring Cost and Reserve [Line Items]
Restructuring charges									24.9
Epoxy \| Employee severance and related benefit costs
Restructuring Cost and Reserve [Line Items]
Restructuring charges									20.6
Epoxy \| Facility exit costs
Restructuring Cost and Reserve [Line Items]
Restructuring charges									38.8
Epoxy \| Lease and other contract termination costs
Restructuring Cost and Reserve [Line Items]
Restructuring charges									38.5
Winchester
Restructuring Cost and Reserve [Line Items]
Restructuring charges	$ 0.0			$ 0.0			$ 0.0	$ 0.0
Other
Restructuring Cost and Reserve [Line Items]
Restructuring charges									3.1
Other \| Write-off of equipment and facility
Restructuring Cost and Reserve [Line Items]
Restructuring charges									0.0
Other \| Employee severance and related benefit costs
Restructuring Cost and Reserve [Line Items]
Restructuring charges									3.1
Other \| Facility exit costs
Restructuring Cost and Reserve [Line Items]
Restructuring charges									0.0
Other \| Lease and other contract termination costs
Restructuring Cost and Reserve [Line Items]
Restructuring charges									$ 0.0