RESTRUCTURING CHARGES (Details 2) - USD ($) $ in Millions	3 Months Ended						9 Months Ended		30 Months Ended	46 Months Ended	95 Months Ended
	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2018	Sep. 30, 2018
Restructuring Cost and Reserve [Line Items]
Restructuring charges	$ 3.3	$ 6.4	$ 4.0	$ 9.2	$ 8.5	$ 8.2	$ 13.7	$ 25.9			$ 200.9
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	0.3	0.1	0.0	0.0	0.0	0.0					23.3
Facility exit costs
Restructuring Cost and Reserve [Line Items]
Restructuring charges	2.7	2.6	3.6	2.2	2.6	2.3					38.9
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	0.0	0.0	0.1	0.2					7.7
Lease and other contract termination costs
Restructuring Cost and Reserve [Line Items]
Restructuring charges	0.3	$ 3.7	$ 0.4	7.0	$ 5.8	$ 5.7					45.3
Chlor Alkali Products and Vinyls Becancour
Restructuring Cost and Reserve [Line Items]
Restructuring charges	0.0			0.4			1.3	2.2		$ 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	$ 3.3			$ 8.8			$ 12.4	$ 23.7	$ 156.4
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									5.9
Chlor Alkali Products and Vinyls Capacity Reductions | Facility exit costs
Restructuring Cost and Reserve [Line Items]
Restructuring charges									30.7
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									$ 40.0
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