RESTRUCTURING CHARGES (Details 2) - USD ($) $ in Millions	3 Months Ended		24 Months Ended	40 Months Ended	89 Months Ended
	Mar. 31, 2018	Mar. 31, 2017	Mar. 31, 2018	Mar. 31, 2018	Mar. 31, 2018
Restructuring Cost and Reserve [Line Items]
Restructuring charges	$ 4.0	$ 8.2			$ 191.2
Write-off of Equipment and Facility
Restructuring Cost and Reserve [Line Items]
Restructuring charges					81.6
Employee severance and job related benefits
Restructuring Cost and Reserve [Line Items]
Restructuring charges	0.0	0.0			22.9
Facility exit costs
Restructuring Cost and Reserve [Line Items]
Restructuring charges	3.6	2.3			33.6
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	0.2			7.7
Lease and other contract termination costs
Restructuring Cost and Reserve [Line Items]
Restructuring charges	0.4	5.7			41.3
Chlor Alkali Products and Vinyls Becancour
Restructuring Cost and Reserve [Line Items]
Restructuring charges	1.0	0.7		$ 17.1
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 job related benefits
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				5.6
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	$ 3.0	$ 7.5	$ 147.0
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 job related benefits
Restructuring Cost and Reserve [Line Items]
Restructuring charges			5.5
Chlor Alkali Products and Vinyls Capacity Reductions | Facility exit costs
Restructuring Cost and Reserve [Line Items]
Restructuring charges			25.7
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			$ 36.0
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 job related benefits
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