RESTRUCTURING CHARGES (Detail Textuals) $ in Millions	12 Months Ended			21 Months Ended	37 Months Ended	86 Months Ended
	Dec. 31, 2017 USD ($)	Dec. 31, 2016 USD ($)	Dec. 31, 2015 USD ($)	Dec. 31, 2017 USD ($)	Dec. 31, 2017 USD ($)	Dec. 31, 2017 USD ($)	Mar. 21, 2016 T	Dec. 31, 2014 USD ($)	Dec. 12, 2014 T	Dec. 31, 2011 USD ($)
Restructuring Cost and Reserve [Line Items]
Restructuring charges	$ 37.6	$ 112.9	$ 2.7			$ 187.2
Restructuring and Related Cost, Incurred Cost						96.0
Restructuring Reserve, Settled without Cash						86.1
Accrued Restructuring Costs	5.1	12.7	6.7	$ 5.1	$ 5.1	5.1		$ 15.7
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	32.6	111.3		144.0
Additional restructuring and related expected cost	22.0			22.0	22.0	22.0
Chlor Alkali Products Becancour
Restructuring Cost and Reserve [Line Items]
Restructuring charges	3.3	0.8	2.0		16.1
Additional restructuring and related expected cost	2.0			2.0	2.0	2.0
Tonnage reduction in chlor alkali manufacturing capacity (in tons) | T									185,000
Winchester Segment
Restructuring Cost and Reserve [Line Items]
Restructuring charges		$ 0.8	$ 0.7			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