RESTRUCTURING CHARGES (Details 2) - USD ($) $ in Millions	3 Months Ended		12 Months Ended	28 Months Ended	77 Months Ended
	Mar. 31, 2017	Mar. 31, 2016	Mar. 31, 2017	Mar. 31, 2017	Mar. 31, 2017
Restructuring Cost and Reserve [Line Items]
Restructuring charges	$ 8.2	$ 92.8			$ 157.8
Write-off of Equipment and Facility
Restructuring Cost and Reserve [Line Items]
Restructuring charges	0.0	76.6			80.1
Employee severance and job related benefits
Restructuring Cost and Reserve [Line Items]
Restructuring charges	0.0	3.9			20.9
Facility exit costs
Restructuring Cost and Reserve [Line Items]
Restructuring charges	2.3	2.9			20.6
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	0.2	0.2			7.6
Lease and other contract termination costs
Restructuring Cost and Reserve [Line Items]
Restructuring charges	5.7	9.2			24.5
Chlor Alkali Products Becancour
Restructuring Cost and Reserve [Line Items]
Restructuring charges	0.7	0.3		$ 13.5
Chlor Alkali Products Becancour | Write-off of Equipment and Facility
Restructuring Cost and Reserve [Line Items]
Restructuring charges				3.5
Chlor Alkali Products Becancour | Employee severance and job related benefits
Restructuring Cost and Reserve [Line Items]
Restructuring charges				2.7
Chlor Alkali Products Becancour | Facility exit costs
Restructuring Cost and Reserve [Line Items]
Restructuring charges				2.0
Chlor Alkali Products Becancour | Pension and other postretirement benefits curtailment
Restructuring Cost and Reserve [Line Items]
Restructuring charges				0.0
Chlor Alkali Products Becancour | Employee relocation costs
Restructuring Cost and Reserve [Line Items]
Restructuring charges				0.0
Chlor Alkali Products 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	$ 7.5	92.2	$ 118.8
Chlor Alkali Products and Vinyls Capacity Reductions | Write-off of Equipment and Facility
Restructuring Cost and Reserve [Line Items]
Restructuring charges			76.6
Chlor Alkali Products and Vinyls Capacity Reductions | Employee severance and job related benefits
Restructuring Cost and Reserve [Line Items]
Restructuring charges			5.1
Chlor Alkali Products and Vinyls Capacity Reductions | Facility exit costs
Restructuring Cost and Reserve [Line Items]
Restructuring charges			16.3
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			1.6
Chlor Alkali Products and Vinyls Capacity Reductions | Lease and other contract termination costs
Restructuring Cost and Reserve [Line Items]
Restructuring charges			$ 19.2
Winchester Segment
Restructuring Cost and Reserve [Line Items]
Restructuring charges		$ 0.3			25.5
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					13.1
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