RESTRUCTURING CHARGES (Details) $ in Millions	1 Months Ended	12 Months Ended			33 Months Ended	49 Months Ended	98 Months Ended
	Dec. 31, 2018 USD ($)	Dec. 31, 2018 USD ($)	Dec. 31, 2017 USD ($)	Dec. 31, 2016 USD ($)	Dec. 31, 2018 USD ($)	Dec. 31, 2018 USD ($)	Dec. 31, 2018 USD ($)	Mar. 21, 2016 T	Dec. 31, 2015 USD ($)
Restructuring Cost and Reserve [Line Items]
Restructuring charges		$ 21.9	$ 37.6	$ 112.9			$ 209.1
Restructuring and Related Cost, Incurred Cost							112.2
Restructuring Reserve, Settled without Cash							88.7
Accrued Restructuring Costs	$ 8.2	8.2	5.1	12.7	$ 8.2	$ 8.2	8.2		$ 6.7
Geelong | Winchester
Restructuring Cost and Reserve [Line Items]
Restructuring charges	4.1
Additional restructuring and related expected cost	1.0	1.0			1.0	1.0	1.0
Capacity Reductions | Chlor Alkali Products and Vinyls
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		15.7	32.6	111.3	159.7
Additional restructuring and related expected cost	10.0	10.0			10.0	10.0	10.0
Becancour | Chlor Alkali Products and Vinyls
Restructuring Cost and Reserve [Line Items]
Restructuring charges		2.1	3.3	0.8		18.2
Additional restructuring and related expected cost	$ 1.0	$ 1.0			$ 1.0	$ 1.0	1.0
Oxford | Winchester
Restructuring Cost and Reserve [Line Items]
Restructuring charges			$ 1.7	$ 0.8			$ 27.1