RESTRUCTURING CHARGES (Details) $ in Millions	1 Months Ended	12 Months Ended			45 Months Ended	61 Months Ended	110 Months Ended
	Dec. 31, 2019 USD ($)	Dec. 31, 2019 USD ($)	Dec. 31, 2018 USD ($)	Dec. 31, 2017 USD ($)	Dec. 31, 2019 USD ($)	Dec. 31, 2019 USD ($)	Dec. 31, 2019 USD ($)	Dec. 11, 2019 T	Dec. 31, 2016 USD ($)	Mar. 21, 2016 T
Restructuring Cost and Reserve [Line Items]
Restructuring charges		$ 76.5	$ 21.9	$ 37.6			$ 285.6
Restructuring and Related Cost, Incurred Cost							134.9
Restructuring Reserve, Settled without Cash							147.6
Accrued Restructuring Costs	$ 3.1	3.1	8.2	5.1	$ 3.1	$ 3.1	3.1		$ 12.7
Freeport | Chlor Alkali Products and Vinyls
Restructuring Cost and Reserve [Line Items]
Freeport Chlor Alkali Capacity Reduction | T								230,000
Restructuring charges	58.9	58.9
Additional restructuring and related expected cost	50.0	50.0			50.0	50.0	50.0
Geelong | Winchester
Restructuring Cost and Reserve [Line Items]
Restructuring charges		0.4	4.1
Other Winchester | Winchester
Restructuring Cost and Reserve [Line Items]
Restructuring charges		1.4
Capacity Reductions | Chlor Alkali Products and Vinyls
Restructuring Cost and Reserve [Line Items]
Restructuring charges		15.8	15.7	32.6	175.5
Additional restructuring and related expected cost	$ 5.0	$ 5.0			$ 5.0	5.0	5.0
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
Becancour | Chlor Alkali Products and Vinyls
Restructuring Cost and Reserve [Line Items]
Restructuring charges			$ 2.1	3.3		$ 18.2
Oxford | Winchester
Restructuring Cost and Reserve [Line Items]
Restructuring charges				$ 1.7			$ 27.1