SEGMENT INFORMATION (Details 2) - USD ($) $ in Millions	3 Months Ended								12 Months Ended
	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Disaggregation of Revenue [Line Items]
Sales	$ 1,387.1	$ 1,576.6	$ 1,592.9	$ 1,553.4	$ 1,635.0	$ 1,872.4	$ 1,728.4	$ 1,710.3	$ 6,110.0	$ 6,946.1	$ 6,268.4
U.S.
Disaggregation of Revenue [Line Items]
Sales									3,599.5	3,944.4	3,556.1
Europe
Disaggregation of Revenue [Line Items]
Sales									990.4	1,183.9	1,082.5
Other foreign
Disaggregation of Revenue [Line Items]
Sales									1,520.1	1,817.8	1,629.8
Chlor Alkali Products and Vinyls
Disaggregation of Revenue [Line Items]
Sales									3,420.1	3,986.7	3,500.8
Chlor Alkali Products and Vinyls | Caustic soda
Disaggregation of Revenue [Line Items]
Sales									1,737.4	2,198.6	1,904.3
Chlor Alkali Products and Vinyls | Chlorine, chlorine derivatives and other co-products
Disaggregation of Revenue [Line Items]
Sales									1,682.7	1,788.1	1,596.5
Chlor Alkali Products and Vinyls | U.S.
Disaggregation of Revenue [Line Items]
Sales									2,332.1	2,610.7	2,294.4
Chlor Alkali Products and Vinyls | Europe
Disaggregation of Revenue [Line Items]
Sales									134.5	181.8	130.1
Chlor Alkali Products and Vinyls | Other foreign
Disaggregation of Revenue [Line Items]
Sales									953.5	1,194.2	1,076.3
Epoxy
Disaggregation of Revenue [Line Items]
Sales									2,024.4	2,303.1	2,086.4
Epoxy | Aromatics and allylics
Disaggregation of Revenue [Line Items]
Sales									945.3	1,145.7	1,051.1
Epoxy | Epoxy resins
Disaggregation of Revenue [Line Items]
Sales									1,079.1	1,157.4	1,035.3
Epoxy | U.S.
Disaggregation of Revenue [Line Items]
Sales									664.0	742.7	646.5
Epoxy | Europe
Disaggregation of Revenue [Line Items]
Sales									844.2	991.1	940.8
Epoxy | Other foreign
Disaggregation of Revenue [Line Items]
Sales									516.2	569.3	499.1
Winchester
Disaggregation of Revenue [Line Items]
Sales									665.5	656.3	681.2
Winchester | Commercial
Disaggregation of Revenue [Line Items]
Sales									441.3	427.6	471.0
Winchester | Military and law enforcement
Disaggregation of Revenue [Line Items]
Sales									224.2	228.7	210.2
Winchester | U.S.
Disaggregation of Revenue [Line Items]
Sales									603.4	591.0	615.2
Winchester | Europe
Disaggregation of Revenue [Line Items]
Sales									11.7	11.0	11.6
Winchester | Other foreign
Disaggregation of Revenue [Line Items]
Sales									$ 50.4	$ 54.3	$ 54.4