RESTRUCTURING CHARGES (Details Textuals) $ in Millions	3 Months Ended				6 Months Ended		27 Months Ended	43 Months Ended	92 Months Ended
	Jun. 30, 2018 USD ($)	Mar. 31, 2018 USD ($)	Jun. 30, 2017 USD ($)	Mar. 31, 2017 USD ($)	Jun. 30, 2018 USD ($)	Jun. 30, 2017 USD ($)	Jun. 30, 2018 USD ($)	Jun. 30, 2018 USD ($)	Jun. 30, 2018 USD ($)	Dec. 31, 2017 USD ($)	Dec. 31, 2016 USD ($)	Mar. 21, 2016 T	Dec. 12, 2014 T	Dec. 31, 2011 USD ($)
Restructuring Cost and Reserve [Line Items]
Restructuring charges	$ 6.4	$ 4.0	$ 8.5	$ 8.2	$ 10.4	$ 16.7			$ 197.6
Inception to date Amounts Utilized (cash)									103.4
Inception to date Amounts Utilized (non-cash)									86.1
Accrued restructuring costs	8.1		17.3		8.1	17.3	$ 8.1	$ 8.1	8.1	$ 5.1	$ 12.7
Chlor Alkali Products and Vinyls Capacity Reductions
Restructuring Cost and Reserve [Line Items]
Total Product Segment Production Capacity Decrease | T												433,000
Henderson Product Segment Production Capacity Decrease | T												153,000
Niagara Product Segment Production Capacity | T												300,000
Reduced Niagara Segment Production Capacity | T												240,000
Freeport Product Segment Production Capacity Decrease | T												220,000
Restructuring charges	6.1		7.4		9.1	14.9	153.1
Additional restructuring and related expected cost	17.0				17.0		17.0	17.0	17.0
Chlor Alkali Products and Vinyls Becancour
Restructuring Cost and Reserve [Line Items]
Restructuring charges	0.3		$ 1.1		1.3	$ 1.8		17.4
Additional restructuring and related expected cost	1.0				1.0		1.0	1.0	1.0
Tonnage reduction in chlor alkali manufacutring capactiy (in tons) | T													185,000
Winchester Segment
Restructuring Cost and Reserve [Line Items]
Restructuring charges									27.1
Estimated Project Cost For Plant Relocation	110.0				110.0		110.0	110.0	110.0
Estimated Capital Spending For Facility Relocation	$ 80.0				$ 80.0		$ 80.0	$ 80.0	$ 80.0
Government Grants for Facility Relocation Capital Spending														$ 31.0