SEGMENT INFORMATION (Details 3) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Disaggregation of Revenue [Line Items]
Sales	$ 1,437.6	$ 1,576.6	$ 4,103.9	$ 4,722.9
Chlor Alkali Products and Vinyls
Disaggregation of Revenue [Line Items]
Sales	755.1	876.3	2,166.2	2,657.7
Chlor Alkali Products and Vinyls | Caustic soda
Disaggregation of Revenue [Line Items]
Sales	373.0	421.7	1,053.4	1,344.8
Chlor Alkali Products and Vinyls | Chlorine, chlorine-derivatives and other co-products
Disaggregation of Revenue [Line Items]
Sales	382.1	454.6	1,112.8	1,312.9
Epoxy
Disaggregation of Revenue [Line Items]
Sales	476.1	511.6	1,350.7	1,554.4
Epoxy | Aromatics and allylics
Disaggregation of Revenue [Line Items]
Sales	198.3	237.9	582.7	716.5
Epoxy | Epoxy resins
Disaggregation of Revenue [Line Items]
Sales	277.8	273.7	768.0	837.9
Winchester
Disaggregation of Revenue [Line Items]
Sales	206.4	188.7	587.0	510.8
Winchester | Commercial
Disaggregation of Revenue [Line Items]
Sales	152.4	131.0	415.1	341.0
Winchester | Military and law enforcement
Disaggregation of Revenue [Line Items]
Sales	$ 54.0	$ 57.7	$ 171.9	$ 169.8