RESTRUCTURING CHARGES (Details 1) $ in Millions	3 Months Ended		12 Months Ended	13 Months Ended	14 Months Ended	28 Months Ended	72 Months Ended
	Mar. 31, 2022 USD ($)	Mar. 31, 2021 USD ($)	Mar. 31, 2022 USD ($)	Mar. 31, 2022 USD ($)	Mar. 31, 2022 USD ($)	Mar. 31, 2022 USD ($)	Mar. 31, 2022 USD ($)	Oct. 21, 2021 T	Mar. 15, 2021 T	Dec. 11, 2019 T	Mar. 21, 2016 T
Restructuring Cost and Reserve [Line Items]
Restructuring charges	$ 3.1	$ 6.9					$ 274.4
Inception to date Amounts Utilized (cash)							125.7
Inception to date Amounts Utilized (non-cash)							138.5
Productivity Plan | Corporate/other
Restructuring Cost and Reserve [Line Items]
Restructuring charges			$ 10.3
Additional restructuring and related expected cost	0.0		0.0	$ 0.0	$ 0.0	$ 0.0	0.0
McIntosh Plan | Chlor Alkali Products and Vinyls
Restructuring Cost and Reserve [Line Items]
Restructuring charges	0.9	4.4		6.5
Additional restructuring and related expected cost	35.0		35.0	35.0	35.0	35.0	35.0
McIntosh Restructuring Capacity Reduction Percent								50.00%	50.00%
McIntosh Restructuring Capacity Reduction | T								200,000	200,000
Freeport 2021 Plan | Chlor Alkali Products and Vinyls
Restructuring Cost and Reserve [Line Items]
Restructuring charges	0.3	1.3			6.8
Additional restructuring and related expected cost	20.0		20.0	20.0	20.0	20.0	20.0
Freeport 2019 Plan | Chlor Alkali Products and Vinyls
Restructuring Cost and Reserve [Line Items]
Restructuring charges	1.7	0.8				68.3
Additional restructuring and related expected cost	40.0		40.0	40.0	40.0	40.0	40.0
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	0.2	$ 0.4					182.5
Additional restructuring and related expected cost	$ 1.0		$ 1.0	$ 1.0	$ 1.0	$ 1.0	$ 1.0
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