RESTRUCTURING CHARGES (Details 3) - USD ($) $ in Millions	3 Months Ended						9 Months Ended		10 Months Ended	22 Months Ended	54 Months Ended
	Sep. 30, 2020	Jun. 30, 2020	Mar. 31, 2020	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2020	Sep. 30, 2020
Restructuring Cost and Reserve [Line Items]
Restructuring charges	$ 1.3	$ 1.7	$ 1.7	$ 4.9	$ 3.8	$ 4.0	$ 4.7	$ 12.7			$ 245.0
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	0.0	0.0	0.1	0.3	0.4	1.4					9.4
Facility exit costs
Restructuring Cost and Reserve [Line Items]
Restructuring charges	1.0	1.7	1.5	4.5	3.2	2.5					52.6
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	0.3	$ 0.0	$ 0.1	0.1	$ 0.2	$ 0.1					41.7
Freeport | Chlor Alkali Products and Vinyls
Restructuring Cost and Reserve [Line Items]
Restructuring charges	0.3						0.8		$ 59.7
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									0.8
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	$ 1.0			$ 4.8			$ 3.9	$ 10.9			179.4
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											51.6
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											$ 41.3
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