RESTRUCTURING CHARGES (Details 2) - USD ($) $ in Millions	12 Months Ended			13 Months Ended	25 Months Ended	57 Months Ended	73 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2020	Dec. 31, 2020	Dec. 31, 2020	Dec. 31, 2020
Restructuring Cost and Reserve [Line Items]
Restructuring charges	$ 9.0	$ 76.5	$ 21.9				$ 267.5
Write-off of equipment and facility
Restructuring Cost and Reserve [Line Items]
Restructuring charges	0.0	58.9	2.6				143.1
Employee severance and related benefit costs
Restructuring Cost and Reserve [Line Items]
Restructuring charges	2.2	2.1	1.7				14.2
Facility exit costs
Restructuring Cost and Reserve [Line Items]
Restructuring charges	5.4	14.6	12.0				59.8
Employee Relocation
Restructuring Cost and Reserve [Line Items]
Restructuring charges							1.7
Lease and other contract termination costs
Restructuring Cost and Reserve [Line Items]
Restructuring charges	1.4	0.9	5.6				48.7
Becancour | Chlor Alkali Products and Vinyls
Restructuring Cost and Reserve [Line Items]
Restructuring charges			2.1				18.2
Becancour | Chlor Alkali Products and Vinyls | Write-off of equipment and facility
Restructuring Cost and Reserve [Line Items]
Restructuring charges							3.5
Becancour | Chlor Alkali Products and Vinyls | Employee severance and related benefit costs
Restructuring Cost and Reserve [Line Items]
Restructuring charges							2.7
Becancour | Chlor Alkali Products and Vinyls | Facility exit costs
Restructuring Cost and Reserve [Line Items]
Restructuring charges							5.9
Becancour | Chlor Alkali Products and Vinyls | Employee Relocation
Restructuring Cost and Reserve [Line Items]
Restructuring charges							0.0
Becancour | Chlor Alkali Products and Vinyls | Lease and other contract termination costs
Restructuring Cost and Reserve [Line Items]
Restructuring charges							$ 6.1
Capacity Reductions | Chlor Alkali Products and Vinyls
Restructuring Cost and Reserve [Line Items]
Restructuring charges	5.2	15.8	$ 15.7			$ 180.7
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						52.0
Capacity Reductions | Chlor Alkali Products and Vinyls | Employee Relocation
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						$ 42.2
Freeport | Chlor Alkali Products and Vinyls
Restructuring Cost and Reserve [Line Items]
Restructuring charges	$ 3.8	$ 58.9		$ 62.7
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				2.1
Freeport | Chlor Alkali Products and Vinyls | Facility exit costs
Restructuring Cost and Reserve [Line Items]
Restructuring charges				1.7
Freeport | Chlor Alkali Products and Vinyls | Employee Relocation
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
Other Winchester | Winchester
Restructuring Cost and Reserve [Line Items]
Restructuring charges					$ 5.9
Other Winchester | Winchester | Write-off of equipment and facility
Restructuring Cost and Reserve [Line Items]
Restructuring charges					2.6
Other Winchester | Winchester | Employee severance and related benefit costs
Restructuring Cost and Reserve [Line Items]
Restructuring charges					2.7
Other Winchester | Winchester | Facility exit costs
Restructuring Cost and Reserve [Line Items]
Restructuring charges					0.2
Other Winchester | Winchester | Employee Relocation
Restructuring Cost and Reserve [Line Items]
Restructuring charges					0.0
Other Winchester | Winchester | Lease and other contract termination costs
Restructuring Cost and Reserve [Line Items]
Restructuring charges					$ 0.4