RESTRUCTURING CHARGES (Details Textuals) $ in Millions	3 Months Ended						9 Months Ended		30 Months Ended	46 Months Ended	95 Months Ended
	Sep. 30, 2018 USD ($)	Jun. 30, 2018 USD ($)	Mar. 31, 2018 USD ($)	Sep. 30, 2017 USD ($)	Jun. 30, 2017 USD ($)	Mar. 31, 2017 USD ($)	Sep. 30, 2018 USD ($)	Sep. 30, 2017 USD ($)	Sep. 30, 2018 USD ($)	Sep. 30, 2018 USD ($)	Sep. 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	$ 3.3	$ 6.4	$ 4.0	$ 9.2	$ 8.5	$ 8.2	$ 13.7	$ 25.9			$ 200.9
Inception to date Amounts Utilized (cash)											107.3
Inception to date Amounts Utilized (non-cash)											86.1
Accrued restructuring costs	7.5			21.9			7.5	21.9	$ 7.5	$ 7.5	7.5	$ 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	3.3			8.8			12.4	23.7	156.4
Additional restructuring and related expected cost	14.0						14.0		14.0	14.0	14.0
Chlor Alkali Products and Vinyls Becancour
Restructuring Cost and Reserve [Line Items]
Restructuring charges	0.0			$ 0.4			1.3	$ 2.2		17.4
Tonnage reduction in chlor alkali manufacutring capactiy (in tons) | T															185,000
Additional restructuring and related expected cost	1.0						1.0		1.0	1.0	1.0
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