RESTRUCTURING CHARGES (Details 2) - USD ($) $ in Millions	1 Months Ended	12 Months Ended			33 Months Ended	49 Months Ended	98 Months Ended
	Dec. 31, 2018	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2018	Dec. 31, 2018	Dec. 31, 2018
Restructuring Cost and Reserve [Line Items]
Restructuring charges		$ 21.9	$ 37.6	$ 112.9			$ 209.1
Write-off of equipment and facility
Restructuring Cost and Reserve [Line Items]
Restructuring charges		2.6	1.5	76.6			84.2
Employee severance and related benefit costs
Restructuring Cost and Reserve [Line Items]
Restructuring charges		1.7	2.0	5.1			24.6
Facility exit costs
Restructuring Cost and Reserve [Line Items]
Restructuring charges		12.0	11.7	15.5			42.0
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	0.3	2.1			7.7
Lease and other contract termination costs
Restructuring Cost and Reserve [Line Items]
Restructuring charges		5.6	22.1	13.6			46.5
Capacity Reductions | Chlor Alkali Products and Vinyls
Restructuring Cost and Reserve [Line Items]
Restructuring charges		15.7	32.6	111.3	$ 159.7
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					5.9
Capacity Reductions | Chlor Alkali Products and Vinyls | Facility exit costs
Restructuring Cost and Reserve [Line Items]
Restructuring charges					33.8
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					$ 40.2
Becancour | Chlor Alkali Products and Vinyls
Restructuring Cost and Reserve [Line Items]
Restructuring charges		$ 2.1	3.3	0.8		$ 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	$ 4.1
Geelong | Winchester | Write-off of equipment and facility
Restructuring Cost and Reserve [Line Items]
Restructuring charges	2.6
Geelong | Winchester | Employee severance and related benefit costs
Restructuring Cost and Reserve [Line Items]
Restructuring charges	1.3
Geelong | Winchester | Facility exit costs
Restructuring Cost and Reserve [Line Items]
Restructuring charges	0.0
Geelong | Winchester | Pension and other postretirement benefits curtailment
Restructuring Cost and Reserve [Line Items]
Restructuring charges	0.0
Geelong | Winchester | Employee relocation costs
Restructuring Cost and Reserve [Line Items]
Restructuring charges	0.0
Geelong | Winchester | Lease and other contract termination costs
Restructuring Cost and Reserve [Line Items]
Restructuring charges	$ 0.2
Oxford | Winchester
Restructuring Cost and Reserve [Line Items]
Restructuring charges			$ 1.7	$ 0.8			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