RESTRUCTURING CHARGES (Details Textuals) $ in Millions	3 Months Ended		24 Months Ended	40 Months Ended	89 Months Ended
	Mar. 31, 2018 USD ($)	Mar. 31, 2017 USD ($)	Mar. 31, 2018 USD ($)	Mar. 31, 2018 USD ($)	Mar. 31, 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	$ 4.0	$ 8.2			$ 191.2
Inception to date Amounts Utilized (cash)					98.8
Inception to date Amounts Utilized (non-cash)					86.1
Accrued restructuring costs	6.3	14.4	$ 6.3	$ 6.3	6.3	$ 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	3.0	7.5	147.0
Additional restructuring and related expected cost	19.0		19.0	19.0	19.0
Chlor Alkali Products and Vinyls Becancour
Restructuring Cost and Reserve [Line Items]
Restructuring charges	1.0	$ 0.7		17.1
Additional restructuring and related expected cost	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
Estimated Capital Spending For Facility Relocation	$ 80.0		$ 80.0	$ 80.0	$ 80.0
Government Grants for Facility Relocation Capital Spending										$ 31.0