GOODWILL AND INTANGIBLES (Details 1) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020	Dec. 31, 2020	Dec. 31, 2019
Goodwill [Line Items]
Goodwill	$ 1,420.1	$ 2,119.6	$ 1,420.2	$ 2,119.7
Foreign currency translation adjustment	(0.1)	(0.1)
Goodwill, Accumulated Impairment Loss	699.8
Chlor Alkali Products and Vinyls
Goodwill [Line Items]
Goodwill	1,275.2	1,832.6	1,275.3	1,832.7
Foreign currency translation adjustment	(0.1)	(0.1)
Goodwill, Accumulated Impairment Loss	557.6
Epoxy
Goodwill [Line Items]
Goodwill	144.9	287.0	$ 144.9	$ 287.0
Foreign currency translation adjustment	0.0	$ 0.0
Goodwill, Accumulated Impairment Loss	$ 142.2