SEGMENT INFORMATION (Details 1) - USD ($) $ in Millions	3 Months Ended								12 Months Ended			73 Months Ended
	Dec. 31, 2020	Sep. 30, 2020	Jun. 30, 2020	Mar. 31, 2020	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2020
Sales [Abstract]
Sales	$ 1,654.1	$ 1,437.6	$ 1,241.2	$ 1,425.1	$ 1,387.1	$ 1,576.6	$ 1,592.9	$ 1,553.4	$ 5,758.0	$ 6,110.0	$ 6,946.1
Income (loss) before taxes [Abstract]
Income (loss) before taxes									1,020.0	36.9	(437.3)
Environmental (expense) income									20.9	20.5	(103.7)
Restructuring charges									(9.0)	(76.5)	(21.9)	$ (267.5)
Acquisition-related costs									0.0	0.0	(1.0)
Goodwill impairment									699.8	0.0	0.0
Other operating income									0.7	0.4	6.4
Interest expense									(292.7)	(243.2)	(243.2)
Interest income									0.5	1.0	1.6
Non-operating pension income									18.9	16.3	21.7
Other income									0.0	11.2	0.0
Earnings (losses) of non-consolidated affiliates [Abstract]
Losses of non-consolidated affiliates									0.0	0.0	(19.7)
Depreciation and amortization expense [Abstract]
Total depreciation and amortization expense									568.4	597.4	601.4
Capital spending [Abstract]
Total capital spending									298.9	385.6	385.2
Assets
Total assets	8,270.9				9,187.8				8,270.9	9,187.8		8,270.9
Chlor Alkali Products and Vinyls
Sales [Abstract]
Sales									2,959.9	3,420.1	3,986.7
Income (loss) before taxes [Abstract]
Income (loss) before taxes									(3.5)	(336.7)	(637.1)
Goodwill impairment									557.6
Depreciation and amortization expense [Abstract]
Total depreciation and amortization expense									451.4	470.4	473.1
Capital spending [Abstract]
Total capital spending									180.4	240.3	259.9
Assets
Total assets	6,165.5				6,898.7				6,165.5	6,898.7		6,165.5
Epoxy
Sales [Abstract]
Sales									1,870.5	2,024.4	2,303.1
Income (loss) before taxes [Abstract]
Income (loss) before taxes									(40.8)	(53.9)	(52.8)
Goodwill impairment									142.2
Depreciation and amortization expense [Abstract]
Total depreciation and amortization expense									90.7	100.1	102.4
Capital spending [Abstract]
Total capital spending									33.7	30.0	36.3
Assets
Total assets	1,153.2				1,469.1				1,153.2	1,469.1		1,153.2
Winchester
Sales [Abstract]
Sales									927.6	665.5	656.3
Income (loss) before taxes [Abstract]
Income (loss) before taxes									(92.3)	(40.1)	(38.4)
Depreciation and amortization expense [Abstract]
Total depreciation and amortization expense									20.1	20.1	20.0
Capital spending [Abstract]
Total capital spending									24.5	12.1	14.7
Assets
Total assets	468.2				385.0				468.2	385.0		468.2
Corporate/Other
Income (loss) before taxes [Abstract]
Environmental (expense) income									(20.9)	(20.5)	103.7
Other corporate and unallocated costs									(154.3)	(156.3)	(158.3)
Restructuring charges									(9.0)	(76.5)	(21.9)
Acquisition-related costs									0.0	0.0	(1.0)
Depreciation and amortization expense [Abstract]
Total depreciation and amortization expense									6.2	6.8	5.9
Capital spending [Abstract]
Total capital spending									60.3	103.2	$ 74.3
Assets
Total assets	$ 484.0				$ 435.0				$ 484.0	$ 435.0		$ 484.0