SEGMENT INFORMATION (Details 1) - USD ($) $ in Millions	3 Months Ended								12 Months Ended			110 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	Dec. 31, 2019
Sales [Abstract]
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
Income (loss) before taxes [Abstract]
Income (loss) before taxes									36.9	(437.3)	(117.2)
Environmental (expense) income									20.5	(103.7)	8.5
Restructuring charges									(76.5)	(21.9)	(37.6)	$ (285.6)
Acquisition-related costs									0.0	(1.0)	(12.8)
Other operating income									0.4	6.4	3.3
Interest expense									(243.2)	(243.2)	(217.4)
Interest income									1.0	1.6	1.8
Non-operating pension income									16.3	21.7	34.4
Other income									11.2	0.0	0.0
Earnings (losses) of non-consolidated affiliates [Abstract]
Earnings (losses) of non-consolidated affiliates									0.0	(19.7)	1.8
Depreciation and amortization expense [Abstract]
Total depreciation and amortization expense									597.4	601.4	558.9
Capital spending [Abstract]
Total capital spending									385.6	385.2	294.3
Assets
Total assets	9,187.8				8,997.4				9,187.8	8,997.4		9,187.8
Investments-Affiliated Companies (at equity) [Abstract]
Investments in non-consolidated affiliates	0.0				8.8				0.0	8.8		0.0
Chlor Alkali Products and Vinyls
Sales [Abstract]
Sales									3,420.1	3,986.7	3,500.8
Income (loss) before taxes [Abstract]
Income (loss) before taxes									(336.7)	(637.1)	(405.8)
Depreciation and amortization expense [Abstract]
Total depreciation and amortization expense									470.4	473.1	432.2
Capital spending [Abstract]
Total capital spending									240.3	259.9	209.5
Assets
Total assets	6,898.7				6,837.2				6,898.7	6,837.2		6,898.7
Investments-Affiliated Companies (at equity) [Abstract]
Investments in non-consolidated affiliates	0.0				8.8				0.0	8.8		0.0
Epoxy
Sales [Abstract]
Sales									2,024.4	2,303.1	2,086.4
Income (loss) before taxes [Abstract]
Income (loss) before taxes									(53.9)	(52.8)	11.8
Depreciation and amortization expense [Abstract]
Total depreciation and amortization expense									100.1	102.4	94.3
Capital spending [Abstract]
Total capital spending									30.0	36.3	37.9
Assets
Total assets	1,469.1				1,521.9				1,469.1	1,521.9		1,469.1
Winchester
Sales [Abstract]
Sales									665.5	656.3	681.2
Income (loss) before taxes [Abstract]
Income (loss) before taxes									(40.1)	(38.4)	(72.4)
Depreciation and amortization expense [Abstract]
Total depreciation and amortization expense									20.1	20.0	19.5
Capital spending [Abstract]
Total capital spending									12.1	14.7	22.5
Assets
Total assets	385.0				399.9				385.0	399.9		385.0
Corporate/Other
Income (loss) before taxes [Abstract]
Environmental (expense) income									(20.5)	103.7	(8.5)
Other corporate and unallocated costs									(156.3)	(158.3)	(112.4)
Restructuring charges									(76.5)	(21.9)	(37.6)
Acquisition-related costs									0.0	(1.0)	(12.8)
Depreciation and amortization expense [Abstract]
Total depreciation and amortization expense									6.8	5.9	12.9
Capital spending [Abstract]
Total capital spending									103.2	74.3	$ 24.4
Assets
Total assets	$ 435.0				$ 238.4				$ 435.0	$ 238.4		$ 435.0