RESTRUCTURING CHARGES (Details 3) - USD ($) $ in Millions	3 Months Ended		4 Months Ended	16 Months Ended	48 Months Ended
	Mar. 31, 2020	Mar. 31, 2019	Mar. 31, 2020	Mar. 31, 2020	Mar. 31, 2020
Restructuring Cost and Reserve [Line Items]
Restructuring charges	$ 1.7	$ 4.0			$ 242.0
Write-off of equipment and facility
Restructuring Cost and Reserve [Line Items]
Restructuring charges					139.6
Employee severance and related benefit costs
Restructuring Cost and Reserve [Line Items]
Restructuring charges	0.1	1.4			9.4
Facility exit costs
Restructuring Cost and Reserve [Line Items]
Restructuring charges	1.5	2.5			49.9
Employee relocation costs
Restructuring Cost and Reserve [Line Items]
Restructuring charges					1.7
Lease and other contract termination costs
Restructuring Cost and Reserve [Line Items]
Restructuring charges	0.1	0.1			41.4
Freeport | Chlor Alkali Products and Vinyls
Restructuring Cost and Reserve [Line Items]
Restructuring charges			$ 58.9
Freeport | Chlor Alkali Products and Vinyls | Write-off of equipment and facility
Restructuring Cost and Reserve [Line Items]
Restructuring charges			58.9
Freeport | Chlor Alkali Products and Vinyls | Employee severance and related benefit costs
Restructuring Cost and Reserve [Line Items]
Restructuring charges			0.0
Freeport | Chlor Alkali Products and Vinyls | Facility exit costs
Restructuring Cost and Reserve [Line Items]
Restructuring charges			0.0
Freeport | Chlor Alkali Products and Vinyls | Employee relocation costs
Restructuring Cost and Reserve [Line Items]
Restructuring charges			0.0
Freeport | Chlor Alkali Products and Vinyls | Lease and other contract termination costs
Restructuring Cost and Reserve [Line Items]
Restructuring charges			$ 0.0
Capacity Reductions | Chlor Alkali Products and Vinyls
Restructuring Cost and Reserve [Line Items]
Restructuring charges	$ 1.7	$ 2.5			177.2
Capacity Reductions | Chlor Alkali Products and Vinyls | Write-off of equipment and facility
Restructuring Cost and Reserve [Line Items]
Restructuring charges					78.1
Capacity Reductions | Chlor Alkali Products and Vinyls | Employee severance and related benefit costs
Restructuring Cost and Reserve [Line Items]
Restructuring charges					6.7
Capacity Reductions | Chlor Alkali Products and Vinyls | Facility exit costs
Restructuring Cost and Reserve [Line Items]
Restructuring charges					49.7
Capacity Reductions | Chlor Alkali Products and Vinyls | Employee relocation costs
Restructuring Cost and Reserve [Line Items]
Restructuring charges					1.7
Capacity Reductions | Chlor Alkali Products and Vinyls | Lease and other contract termination costs
Restructuring Cost and Reserve [Line Items]
Restructuring charges					$ 41.0
Total Winchester | Winchester
Restructuring Cost and Reserve [Line Items]
Restructuring charges				$ 5.9
Total Winchester | Winchester | Write-off of equipment and facility
Restructuring Cost and Reserve [Line Items]
Restructuring charges				2.6
Total Winchester | Winchester | Employee severance and related benefit costs
Restructuring Cost and Reserve [Line Items]
Restructuring charges				2.7
Total Winchester | Winchester | Facility exit costs
Restructuring Cost and Reserve [Line Items]
Restructuring charges				0.2
Total Winchester | Winchester | Employee relocation costs
Restructuring Cost and Reserve [Line Items]
Restructuring charges				0.0
Total Winchester | Winchester | Lease and other contract termination costs
Restructuring Cost and Reserve [Line Items]
Restructuring charges				$ 0.4