SEGMENT INFORMATION (Details 1) - USD ($) $ in Millions	3 Months Ended								12 Months Ended			98 Months Ended
	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2018
Sales [Abstract]
Sales	$ 1,635.0	$ 1,872.4	$ 1,728.4	$ 1,710.3	$ 1,619.9	$ 1,554.9	$ 1,526.5	$ 1,567.1	$ 6,946.1	$ 6,268.4	$ 5,550.6
Income (loss) before taxes [Abstract]
Income (loss) before taxes									(437.3)	(117.2)	34.2
Environmental income (expense)									(103.7)	8.5	9.2
Restructuring charge									(21.9)	(37.6)	(112.9)	$ (209.1)
Acquisition-related costs									(1.0)	(12.8)	(48.8)
Other operating income									6.4	3.3	10.6
Interest expense									(243.2)	(217.4)	(191.9)
Interest income									1.6	1.8	3.4
Non-operating pension income									21.7	34.4	44.8
Earnings (losses) of non-consolidated affiliates [Abstract]
Earnings (losses) of non-consolidated affiliates									(19.7)	1.8	1.7
Depreciation and amortization expense [Abstract]
Total depreciation and amortization expense									601.4	558.9	533.5
Capital spending [Abstract]
Total capital spending									385.2	294.3	278.0
Assets
Total assets	8,997.4				9,218.3				8,997.4	9,218.3		8,997.4
Investments-Affiliated Companies (at equity) [Abstract]
Investments in non-consolidated affiliates	8.8				28.5				8.8	28.5		8.8
Chlor Alkali Products and Vinyls
Sales [Abstract]
Sales									3,986.7	3,500.8	2,999.3
Income (loss) before taxes [Abstract]
Income (loss) before taxes									(637.1)	(405.8)	(224.9)
Depreciation and amortization expense [Abstract]
Total depreciation and amortization expense									473.1	432.2	418.1
Capital spending [Abstract]
Total capital spending									259.9	209.5	195.1
Assets
Total assets	6,837.2				7,008.0				6,837.2	7,008.0		6,837.2
Investments-Affiliated Companies (at equity) [Abstract]
Investments in non-consolidated affiliates	8.8				28.5				8.8	28.5		8.8
Epoxy
Sales [Abstract]
Sales									2,303.1	2,086.4	1,822.0
Income (loss) before taxes [Abstract]
Income (loss) before taxes									(52.8)	11.8	(15.4)
Depreciation and amortization expense [Abstract]
Total depreciation and amortization expense									102.4	94.3	90.0
Capital spending [Abstract]
Total capital spending									36.3	37.9	45.4
Assets
Total assets	1,521.9				1,597.1				1,521.9	1,597.1		1,521.9
Winchester
Sales [Abstract]
Sales									656.3	681.2	729.3
Income (loss) before taxes [Abstract]
Income (loss) before taxes									(38.4)	(72.4)	(120.9)
Depreciation and amortization expense [Abstract]
Total depreciation and amortization expense									20.0	19.5	18.5
Capital spending [Abstract]
Total capital spending									14.7	22.5	19.5
Assets
Total assets	399.9				425.2				399.9	425.2		399.9
Corporate/Other
Income (loss) before taxes [Abstract]
Environmental income (expense)									103.7	(8.5)	(9.2)
Other corporate and unallocated costs									(158.3)	(112.4)	(91.4)
Restructuring charge									(21.9)	(37.6)	(112.9)
Acquisition-related costs									(1.0)	(12.8)	(48.8)
Depreciation and amortization expense [Abstract]
Total depreciation and amortization expense									5.9	12.9	6.9
Capital spending [Abstract]
Total capital spending									74.3	24.4	$ 18.0
Assets
Total assets	$ 238.4				$ 188.0				$ 238.4	$ 188.0		$ 238.4