GOODWILL AND INTANGIBLES (Details 1) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017	Dec. 31, 2017	Dec. 31, 2016
Goodwill [Line Items]
Goodwill	$ 2,120.3	$ 2,119.0	$ 2,120.0	$ 2,118.0
Foreign currency translation adjustment	0.3	1.0
Chlor Alkali Products and Vinyls Segment
Goodwill [Line Items]
Goodwill	1,833.1	1,832.1	1,832.9	1,831.3
Foreign currency translation adjustment	0.2	0.8
Epoxy Segment
Goodwill [Line Items]
Goodwill	287.2	286.9	$ 287.1	$ 286.7
Foreign currency translation adjustment	$ 0.1	$ 0.2