RESTRUCTURING CHARGES (Details 1) $ in Millions	3 Months Ended						9 Months Ended		10 Months Ended	54 Months Ended
	Sep. 30, 2020 USD ($)	Jun. 30, 2020 USD ($)	Mar. 31, 2020 USD ($)	Sep. 30, 2019 USD ($)	Jun. 30, 2019 USD ($)	Mar. 31, 2019 USD ($)	Sep. 30, 2020 USD ($)	Sep. 30, 2019 USD ($)	Sep. 30, 2020 USD ($)	Sep. 30, 2020 USD ($)	Dec. 31, 2019 USD ($)	Dec. 11, 2019 T	Dec. 31, 2018 USD ($)	Mar. 21, 2016 T
Restructuring Cost and Reserve [Line Items]
Restructuring charges	$ 1.3	$ 1.7	$ 1.7	$ 4.9	$ 3.8	$ 4.0	$ 4.7	$ 12.7		$ 245.0
Inception to date Amounts Utilized (cash)										102.9
Inception to date Amounts Utilized (non-cash)										139.6
Accrued restructuring costs	2.5			5.2			2.5	5.2	$ 2.5	2.5	$ 3.1		$ 8.2
Freeport | Chlor Alkali Products and Vinyls
Restructuring Cost and Reserve [Line Items]
Freeport Chlor Alkali Capacity Reduction | T												230,000
Restructuring charges	0.3						0.8		59.7
Additional restructuring and related expected cost	50.0						50.0		50.0	50.0
Geelong | Winchester
Restructuring Cost and Reserve [Line Items]
Restructuring charges				0.1				0.4
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	1.0			$ 4.8			3.9	$ 10.9		179.4
Additional restructuring and related expected cost	$ 4.0						$ 4.0		$ 4.0	$ 4.0
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