RESTRUCTURING CHARGES (Details 3) - USD ($) $ in Millions	1 Months Ended	3 Months Ended				4 Months Ended	5 Months Ended	6 Months Ended		19 Months Ended	63 Months Ended
	Jun. 30, 2021	Jun. 30, 2021	Mar. 31, 2021	Jun. 30, 2020	Mar. 31, 2020	Jun. 30, 2021	Jun. 30, 2021	Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2021
Restructuring Cost and Reserve [Line Items]
Restructuring charges		$ 14.0	$ 6.9	$ 1.7	$ 1.7			$ 20.9	$ 3.4		$ 264.3
Write-off of equipment and facility
Restructuring Cost and Reserve [Line Items]
Restructuring charges											137.0
Employee severance and related benefit costs
Restructuring Cost and Reserve [Line Items]
Restructuring charges		10.1	0.0	0.0	0.1						18.9
Facility exit costs
Restructuring Cost and Reserve [Line Items]
Restructuring charges		3.4	2.3	1.7	1.5						59.4
Employee relocation costs
Restructuring Cost and Reserve [Line Items]
Restructuring charges											1.7
Lease and other contract termination costs
Restructuring Cost and Reserve [Line Items]
Restructuring charges		0.5	$ 4.6	0.0	$ 0.1						47.3
Plaquemine Plan | Chlor Alkali Products and Vinyls
Restructuring Cost and Reserve [Line Items]
Restructuring charges	$ 0.0
Plaquemine Plan | Chlor Alkali Products and Vinyls | Write-off of equipment and facility
Restructuring Cost and Reserve [Line Items]
Restructuring charges	0.0
Plaquemine Plan | Chlor Alkali Products and Vinyls | Employee severance and related benefit costs
Restructuring Cost and Reserve [Line Items]
Restructuring charges	0.0
Plaquemine Plan | Chlor Alkali Products and Vinyls | Facility exit costs
Restructuring Cost and Reserve [Line Items]
Restructuring charges	0.0
Plaquemine Plan | Chlor Alkali Products and Vinyls | Employee relocation costs
Restructuring Cost and Reserve [Line Items]
Restructuring charges	0.0
Plaquemine Plan | Chlor Alkali Products and Vinyls | Lease and other contract termination costs
Restructuring Cost and Reserve [Line Items]
Restructuring charges	$ 0.0
McIntosh Plan | Chlor Alkali Products and Vinyls
Restructuring Cost and Reserve [Line Items]
Restructuring charges		0.4				$ 4.8		4.8
McIntosh Plan | Chlor Alkali Products and Vinyls | Write-off of equipment and facility
Restructuring Cost and Reserve [Line Items]
Restructuring charges						0.0
McIntosh Plan | Chlor Alkali Products and Vinyls | Employee severance and related benefit costs
Restructuring Cost and Reserve [Line Items]
Restructuring charges						0.0
McIntosh Plan | Chlor Alkali Products and Vinyls | Facility exit costs
Restructuring Cost and Reserve [Line Items]
Restructuring charges						0.0
McIntosh Plan | Chlor Alkali Products and Vinyls | Employee relocation costs
Restructuring Cost and Reserve [Line Items]
Restructuring charges						0.0
McIntosh Plan | Chlor Alkali Products and Vinyls | Lease and other contract termination costs
Restructuring Cost and Reserve [Line Items]
Restructuring charges						$ 4.8
Freeport 2021 Plan | Chlor Alkali Products and Vinyls
Restructuring Cost and Reserve [Line Items]
Restructuring charges		2.8					$ 4.1	4.1
Freeport 2021 Plan | Chlor Alkali Products and Vinyls | Write-off of equipment and facility
Restructuring Cost and Reserve [Line Items]
Restructuring charges							0.0
Freeport 2021 Plan | Chlor Alkali Products and Vinyls | Employee severance and related benefit costs
Restructuring Cost and Reserve [Line Items]
Restructuring charges							0.0
Freeport 2021 Plan | Chlor Alkali Products and Vinyls | Facility exit costs
Restructuring Cost and Reserve [Line Items]
Restructuring charges							4.1
Freeport 2021 Plan | Chlor Alkali Products and Vinyls | Employee relocation costs
Restructuring Cost and Reserve [Line Items]
Restructuring charges							0.0
Freeport 2021 Plan | Chlor Alkali Products and Vinyls | Lease and other contract termination costs
Restructuring Cost and Reserve [Line Items]
Restructuring charges							$ 0.0
Freeport 2019 Plan | Chlor Alkali Products and Vinyls
Restructuring Cost and Reserve [Line Items]
Restructuring charges		0.4		0.5				1.2	0.5	$ 63.9
Freeport 2019 Plan | Chlor Alkali Products and Vinyls | Write-off of equipment and facility
Restructuring Cost and Reserve [Line Items]
Restructuring charges										58.9
Freeport 2019 Plan | Chlor Alkali Products and Vinyls | Employee severance and related benefit costs
Restructuring Cost and Reserve [Line Items]
Restructuring charges										2.1
Freeport 2019 Plan | Chlor Alkali Products and Vinyls | Facility exit costs
Restructuring Cost and Reserve [Line Items]
Restructuring charges										2.9
Freeport 2019 Plan | Chlor Alkali Products and Vinyls | Employee relocation costs
Restructuring Cost and Reserve [Line Items]
Restructuring charges										0.0
Freeport 2019 Plan | Chlor Alkali Products and Vinyls | Lease and other contract termination costs
Restructuring Cost and Reserve [Line Items]
Restructuring charges										$ 0.0
Chlor Alkali 2016 Plan | Chlor Alkali Products and Vinyls
Restructuring Cost and Reserve [Line Items]
Restructuring charges		0.3		$ 1.2				0.7	$ 2.9		181.4
Chlor Alkali 2016 Plan | Chlor Alkali Products and Vinyls | Write-off of equipment and facility
Restructuring Cost and Reserve [Line Items]
Restructuring charges											78.1
Chlor Alkali 2016 Plan | Chlor Alkali Products and Vinyls | Employee severance and related benefit costs
Restructuring Cost and Reserve [Line Items]
Restructuring charges											6.7
Chlor Alkali 2016 Plan | Chlor Alkali Products and Vinyls | Facility exit costs
Restructuring Cost and Reserve [Line Items]
Restructuring charges											52.4
Chlor Alkali 2016 Plan | Chlor Alkali Products and Vinyls | Employee relocation costs
Restructuring Cost and Reserve [Line Items]
Restructuring charges											1.7
Chlor Alkali 2016 Plan | Chlor Alkali Products and Vinyls | Lease and other contract termination costs
Restructuring Cost and Reserve [Line Items]
Restructuring charges											$ 42.5
Productivity Plan | Corporate/other
Restructuring Cost and Reserve [Line Items]
Restructuring charges		10.1						$ 10.1
Productivity Plan | Corporate/other | Write-off of equipment and facility
Restructuring Cost and Reserve [Line Items]
Restructuring charges		0.0
Productivity Plan | Corporate/other | Employee severance and related benefit costs
Restructuring Cost and Reserve [Line Items]
Restructuring charges		10.1
Productivity Plan | Corporate/other | Facility exit costs
Restructuring Cost and Reserve [Line Items]
Restructuring charges		0.0
Productivity Plan | Corporate/other | Employee relocation costs
Restructuring Cost and Reserve [Line Items]
Restructuring charges		0.0
Productivity Plan | Corporate/other | Lease and other contract termination costs
Restructuring Cost and Reserve [Line Items]
Restructuring charges		$ 0.0