SEGMENT INFORMATION (Details 3) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Disaggregation of Revenue [Line Items]
Sales	$ 2,340.1	$ 1,437.6	$ 6,480.2	$ 4,103.9
Chlor Alkali Products and Vinyls
Disaggregation of Revenue [Line Items]
Sales	1,062.4	755.1	2,896.7	2,166.2
Chlor Alkali Products and Vinyls | Caustic soda
Disaggregation of Revenue [Line Items]
Sales	421.8	373.0	1,169.6	1,053.4
Chlor Alkali Products and Vinyls | Chlorine, chlorine-derivatives and other co-products
Disaggregation of Revenue [Line Items]
Sales	640.6	382.1	1,727.1	1,112.8
Epoxy
Disaggregation of Revenue [Line Items]
Sales	877.7	476.1	2,390.3	1,350.7
Epoxy | Aromatics and allylics
Disaggregation of Revenue [Line Items]
Sales	375.0	198.3	1,053.5	582.7
Epoxy | Epoxy resins
Disaggregation of Revenue [Line Items]
Sales	502.7	277.8	1,336.8	768.0
Winchester
Disaggregation of Revenue [Line Items]
Sales	400.0	206.4	1,193.2	587.0
Winchester | Commercial
Disaggregation of Revenue [Line Items]
Sales	280.9	152.4	823.4	415.1
Winchester | Military and law enforcement
Disaggregation of Revenue [Line Items]
Sales	$ 119.1	$ 54.0	$ 369.8	$ 171.9