SEGMENT INFORMATION (Details 3) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020
Disaggregation of Revenue [Line Items]
Sales	$ 2,221.3	$ 1,241.2	$ 4,140.1	$ 2,666.3
Chlor Alkali Products and Vinyls
Disaggregation of Revenue [Line Items]
Sales	967.3	651.2	1,834.3	1,411.1
Chlor Alkali Products and Vinyls | Caustic soda
Disaggregation of Revenue [Line Items]
Sales	400.8	320.2	747.8	680.4
Chlor Alkali Products and Vinyls | Chlorine, chlorine-derivatives and other co-products
Disaggregation of Revenue [Line Items]
Sales	566.5	331.0	1,086.5	730.7
Epoxy
Disaggregation of Revenue [Line Items]
Sales	850.0	397.4	1,512.6	874.6
Epoxy | Aromatics and allylics
Disaggregation of Revenue [Line Items]
Sales	366.5	167.0	678.5	384.4
Epoxy | Epoxy resins
Disaggregation of Revenue [Line Items]
Sales	483.5	230.4	834.1	490.2
Winchester
Disaggregation of Revenue [Line Items]
Sales	404.0	192.6	793.2	380.6
Winchester | Commercial
Disaggregation of Revenue [Line Items]
Sales	281.5	135.6	542.5	262.7
Winchester | Military and law enforcement
Disaggregation of Revenue [Line Items]
Sales	$ 122.5	$ 57.0	$ 250.7	$ 117.9