RESTRUCTURING CHARGES (Details 2) - USD ($) $ in Millions	3 Months Ended				6 Months Ended		27 Months Ended	43 Months Ended	92 Months Ended
	Jun. 30, 2018	Mar. 31, 2018	Jun. 30, 2017	Mar. 31, 2017	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2018	Jun. 30, 2018
Restructuring Cost and Reserve [Line Items]
Restructuring charges	$ 6.4	$ 4.0	$ 8.5	$ 8.2	$ 10.4	$ 16.7			$ 197.6
Write-off of equipment and facility
Restructuring Cost and Reserve [Line Items]
Restructuring charges									81.6
Employee severance and related benefit costs
Restructuring Cost and Reserve [Line Items]
Restructuring charges	0.1	0.0	0.0	0.0					23.0
Facility exit costs
Restructuring Cost and Reserve [Line Items]
Restructuring charges	2.6	3.6	2.6	2.3					36.2
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	0.1	0.2					7.7
Lease and other contract termination costs
Restructuring Cost and Reserve [Line Items]
Restructuring charges	3.7	$ 0.4	5.8	$ 5.7					45.0
Chlor Alkali Products and Vinyls Becancour
Restructuring Cost and Reserve [Line Items]
Restructuring charges	0.3		1.1		1.3	1.8		$ 17.4
Chlor Alkali Products and Vinyls Becancour | Write-off of equipment and facility
Restructuring Cost and Reserve [Line Items]
Restructuring charges								3.5
Chlor Alkali Products and Vinyls Becancour | Employee severance and related benefit costs
Restructuring Cost and Reserve [Line Items]
Restructuring charges								2.7
Chlor Alkali Products and Vinyls Becancour | Facility exit costs
Restructuring Cost and Reserve [Line Items]
Restructuring charges								5.9
Chlor Alkali Products and Vinyls Becancour | Pension and other postretirement benefits curtailment
Restructuring Cost and Reserve [Line Items]
Restructuring charges								0.0
Chlor Alkali Products and Vinyls Becancour | Employee relocation costs
Restructuring Cost and Reserve [Line Items]
Restructuring charges								0.0
Chlor Alkali Products and Vinyls Becancour | Lease and other contract termination costs
Restructuring Cost and Reserve [Line Items]
Restructuring charges								$ 5.3
Chlor Alkali Products and Vinyls Capacity Reductions
Restructuring Cost and Reserve [Line Items]
Restructuring charges	$ 6.1		$ 7.4		$ 9.1	$ 14.9	$ 153.1
Chlor Alkali Products and Vinyls Capacity Reductions | Write-off of equipment and facility
Restructuring Cost and Reserve [Line Items]
Restructuring charges							78.1
Chlor Alkali Products and Vinyls Capacity Reductions | Employee severance and related benefit costs
Restructuring Cost and Reserve [Line Items]
Restructuring charges							5.6
Chlor Alkali Products and Vinyls Capacity Reductions | Facility exit costs
Restructuring Cost and Reserve [Line Items]
Restructuring charges							28.0
Chlor Alkali Products and Vinyls Capacity Reductions | Pension and other postretirement benefits curtailment
Restructuring Cost and Reserve [Line Items]
Restructuring charges							0.0
Chlor Alkali Products and Vinyls Capacity Reductions | Employee relocation costs
Restructuring Cost and Reserve [Line Items]
Restructuring charges							1.7
Chlor Alkali Products and Vinyls Capacity Reductions | Lease and other contract termination costs
Restructuring Cost and Reserve [Line Items]
Restructuring charges							$ 39.7
Winchester Segment
Restructuring Cost and Reserve [Line Items]
Restructuring charges									27.1
Winchester Segment | Write-off of equipment and facility
Restructuring Cost and Reserve [Line Items]
Restructuring charges									0.0
Winchester Segment | Employee severance and related benefit costs
Restructuring Cost and Reserve [Line Items]
Restructuring charges									14.7
Winchester Segment | Facility exit costs
Restructuring Cost and Reserve [Line Items]
Restructuring charges									2.3
Winchester Segment | Pension and other postretirement benefits curtailment
Restructuring Cost and Reserve [Line Items]
Restructuring charges									4.1
Winchester Segment | Employee relocation costs
Restructuring Cost and Reserve [Line Items]
Restructuring charges									6.0
Winchester Segment | Lease and other contract termination costs
Restructuring Cost and Reserve [Line Items]
Restructuring charges									$ 0.0