GOODWILL AND INTANGIBLE ASSETS (Details 1) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020	Dec. 31, 2020	Dec. 31, 2019
Goodwill [Line Items]
Goodwill	$ 1,420.3	$ 1,420.1	$ 1,420.3	$ 1,420.1	$ 1,420.2	$ 2,119.7
Goodwill impairment	0.0	(699.8)	0.0	(699.8)
Foreign currency translation adjustment			0.1	0.2
Chlor Alkali Products and Vinyls
Goodwill [Line Items]
Goodwill	1,275.4	1,275.3	1,275.4	1,275.3	1,275.3	1,832.7
Goodwill impairment		(557.6)		(557.6)
Foreign currency translation adjustment			0.1	0.2
Epoxy
Goodwill [Line Items]
Goodwill	$ 144.9	144.8	144.9	144.8	$ 144.9	$ 287.0
Goodwill impairment		$ (142.2)		(142.2)
Foreign currency translation adjustment			$ 0.0	$ 0.0