RESTRUCTURING CHARGES (Details 1) $ in Millions	3 Months Ended		4 Months Ended	48 Months Ended
	Mar. 31, 2020 USD ($)	Mar. 31, 2019 USD ($)	Mar. 31, 2020 USD ($)	Mar. 31, 2020 USD ($)	Dec. 31, 2019 USD ($)	Dec. 11, 2019 T	Dec. 31, 2018 USD ($)	Mar. 21, 2016 T
Restructuring Cost and Reserve [Line Items]
Restructuring charges	$ 1.7	$ 4.0		$ 242.0
Inception to date Amounts Utilized (cash)				99.4
Inception to date Amounts Utilized (non-cash)				139.6
Accrued restructuring costs	3.0	8.5	$ 3.0	3.0	$ 3.1		$ 8.2
Freeport | Chlor Alkali Products and Vinyls
Restructuring Cost and Reserve [Line Items]
Freeport Chlor Alkali Capacity Reduction | T						230,000
Additional restructuring and related expected cost	50.0		50.0	50.0
Restructuring charges			58.9
Geelong | Winchester
Restructuring Cost and Reserve [Line Items]
Restructuring charges		0.1
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]
Additional restructuring and related expected cost	5.0		$ 5.0	5.0
Restructuring charges	$ 1.7	$ 2.5		$ 177.2
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