RESTRUCTURING CHARGES (Details 1) $ in Millions	1 Months Ended	2 Months Ended	3 Months Ended		16 Months Ended	60 Months Ended
	Mar. 31, 2021 USD ($)	Mar. 31, 2021 USD ($)	Mar. 31, 2021 USD ($)	Mar. 31, 2020 USD ($)	Mar. 31, 2021 USD ($)	Mar. 31, 2021 USD ($)	Mar. 15, 2021 T	Dec. 11, 2019 T	Mar. 21, 2016 T
Restructuring Cost and Reserve [Line Items]
Restructuring charges			$ 6.9	$ 1.7		$ 250.3
Inception to date Amounts Utilized (cash)						105.7
Inception to date Amounts Utilized (non-cash)						137.0
McIntosh Plan | Chlor Alkali Products and Vinyls
Restructuring Cost and Reserve [Line Items]
McIntosh Restructuring Capacity Reduction Percent							50.00%
McIntosh Restructuring Capacity Reduction Tons | T							200,000
Restructuring charges	$ 4.4		4.4
Additional restructuring and related expected cost	5.0	$ 5.0	5.0		$ 5.0	5.0
Freeport 2021 Plan | Chlor Alkali Products and Vinyls
Restructuring Cost and Reserve [Line Items]
Restructuring charges		1.3	1.3
Additional restructuring and related expected cost	23.0	23.0	23.0		23.0	23.0
Freeport 2019 Plan | Chlor Alkali Products and Vinyls
Restructuring Cost and Reserve [Line Items]
Restructuring charges			0.8		63.5
Additional restructuring and related expected cost	45.0	45.0	45.0		45.0	45.0
Freeport Chlor Alkali Capacity Reduction | T								230,000
Chlor Alkali 2016 Plan | Chlor Alkali Products and Vinyls
Restructuring Cost and Reserve [Line Items]
Restructuring charges			0.4	$ 1.7		181.1
Additional restructuring and related expected cost	$ 2.0	$ 2.0	$ 2.0		$ 2.0	$ 2.0
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