RESTRUCTURING CHARGES (Details 2) - USD ($) $ in Millions	1 Months Ended	12 Months Ended			13 Months Ended	45 Months Ended	61 Months Ended	110 Months Ended
	Dec. 31, 2019	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2019	Dec. 31, 2019	Dec. 31, 2019	Dec. 31, 2019
Restructuring Cost and Reserve [Line Items]
Restructuring charges		$ 76.5	$ 21.9	$ 37.6				$ 285.6
Write-off of equipment and facility
Restructuring Cost and Reserve [Line Items]
Restructuring charges		58.9	2.6	1.5				143.1
Employee severance and related benefit costs
Restructuring Cost and Reserve [Line Items]
Restructuring charges		2.1	1.7	2.0				26.7
Facility exit costs
Restructuring Cost and Reserve [Line Items]
Restructuring charges		14.6	12.0	11.7				56.6
Pension and other postretirement benefits curtailment
Restructuring Cost and Reserve [Line Items]
Restructuring charges								4.1
Employee relocation costs
Restructuring Cost and Reserve [Line Items]
Restructuring charges		0.0	0.0	0.3				7.7
Lease and other contract termination costs
Restructuring Cost and Reserve [Line Items]
Restructuring charges		0.9	5.6	22.1				47.4
Capacity Reductions | Chlor Alkali Products and Vinyls
Restructuring Cost and Reserve [Line Items]
Restructuring charges		15.8	15.7	32.6		$ 175.5
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						6.6
Capacity Reductions | Chlor Alkali Products and Vinyls | Facility exit costs
Restructuring Cost and Reserve [Line Items]
Restructuring charges						48.2
Capacity Reductions | Chlor Alkali Products and Vinyls | Pension and other postretirement benefits curtailment
Restructuring Cost and Reserve [Line Items]
Restructuring charges						0.0
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						$ 40.9
Freeport | Chlor Alkali Products and Vinyls
Restructuring Cost and Reserve [Line Items]
Restructuring charges	$ 58.9	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 | Pension and other postretirement benefits curtailment
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
Becancour | Chlor Alkali Products and Vinyls
Restructuring Cost and Reserve [Line Items]
Restructuring charges			2.1	3.3			$ 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 | Pension and other postretirement benefits curtailment
Restructuring Cost and Reserve [Line Items]
Restructuring charges							0.0
Becancour | Chlor Alkali Products and Vinyls | Employee relocation costs
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
Geelong | Winchester
Restructuring Cost and Reserve [Line Items]
Restructuring charges		$ 0.4	$ 4.1
Oxford | Winchester
Restructuring Cost and Reserve [Line Items]
Restructuring charges				$ 1.7				27.1
Oxford | Winchester | Write-off of equipment and facility
Restructuring Cost and Reserve [Line Items]
Restructuring charges								0.0
Oxford | Winchester | Employee severance and related benefit costs
Restructuring Cost and Reserve [Line Items]
Restructuring charges								14.7
Oxford | Winchester | Facility exit costs
Restructuring Cost and Reserve [Line Items]
Restructuring charges								2.3
Oxford | Winchester | Pension and other postretirement benefits curtailment
Restructuring Cost and Reserve [Line Items]
Restructuring charges								4.1
Oxford | Winchester | Employee relocation costs
Restructuring Cost and Reserve [Line Items]
Restructuring charges								6.0
Oxford | Winchester | 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 | Pension and other postretirement benefits curtailment
Restructuring Cost and Reserve [Line Items]
Restructuring charges					0.0
Other Winchester | Winchester | Employee relocation costs
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