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SEGMENT INFORMATION (Details) - USD ($) $ in Millions	3 Months Ended		89 Months Ended
SEGMENT INFORMATION (Details) - USD ($) $ in Millions	Mar. 31, 2018	Mar. 31, 2017	Mar. 31, 2018
Segment Reporting Information [Line Items]
Sales	$ 1,710.3	$ 1,567.1
Income (loss) before taxes:
Income before taxes	27.5	17.9
Restructuring charges	(4.0)	(8.2)	$ (191.2)
Acquisition-related costs	(0.3)	(7.0)
Other operating income (expense)	8.1	(0.4)
Interest expense	(63.7)	(52.4)
Interest income	0.4	0.2
Non-operating pension income	5.4	8.5
Gain in Other Operating Income (Expense) due to Insurance Recoveries	8.0
Revenue from Contract with Customer, Excluding Assessed Tax [Abstract]
Sales	1,710.3	1,567.1
United States
Revenue from Contract with Customer, Excluding Assessed Tax [Abstract]
Sales	947.1	875.1
Europe
Revenue from Contract with Customer, Excluding Assessed Tax [Abstract]
Sales	325.3	299.6
Other foreign
Revenue from Contract with Customer, Excluding Assessed Tax [Abstract]
Sales	437.9	392.4
Chlor Alkali Products and Vinyls Segment
Segment Reporting Information [Line Items]
Sales	936.1	836.9
Income (loss) before taxes:
Income before taxes	130.5	87.5
Revenue from Contract with Customer, Excluding Assessed Tax [Abstract]
Sales	936.1	836.9
Chlor Alkali Products and Vinyls Segment \| United States
Revenue from Contract with Customer, Excluding Assessed Tax [Abstract]
Sales	608.1	556.7
Chlor Alkali Products and Vinyls Segment \| Europe
Revenue from Contract with Customer, Excluding Assessed Tax [Abstract]
Sales	45.8	29.2
Chlor Alkali Products and Vinyls Segment \| Other foreign
Revenue from Contract with Customer, Excluding Assessed Tax [Abstract]
Sales	282.2	251.0
Epoxy Segment
Segment Reporting Information [Line Items]
Sales	603.3	567.6
Income (loss) before taxes:
Income before taxes	(22.1)	(1.2)
Revenue from Contract with Customer, Excluding Assessed Tax [Abstract]
Sales	603.3	567.6
Epoxy Segment \| United States
Revenue from Contract with Customer, Excluding Assessed Tax [Abstract]
Sales	180.4	163.2
Epoxy Segment \| Europe
Revenue from Contract with Customer, Excluding Assessed Tax [Abstract]
Sales	278.5	269.6
Epoxy Segment \| Other foreign
Revenue from Contract with Customer, Excluding Assessed Tax [Abstract]
Sales	144.4	134.8
Winchester Segment
Segment Reporting Information [Line Items]
Sales	170.9	162.6
Income (loss) before taxes:
Income before taxes	12.0	25.1
Restructuring charges			$ (27.1)
Revenue from Contract with Customer, Excluding Assessed Tax [Abstract]
Sales	170.9	162.6
Winchester Segment \| United States
Revenue from Contract with Customer, Excluding Assessed Tax [Abstract]
Sales	158.6	155.2
Winchester Segment \| Europe
Revenue from Contract with Customer, Excluding Assessed Tax [Abstract]
Sales	1.0	0.8
Winchester Segment \| Other foreign
Revenue from Contract with Customer, Excluding Assessed Tax [Abstract]
Sales	11.3	6.6
CorporateOther [Member]
Income (loss) before taxes:
Environmental expense	(2.3)	(2.6)
Other corporate and unallocated costs	(36.5)	(31.6)
Restructuring charges	(4.0)	(8.2)
Acquisition-related costs	(0.3)	(7.0)
Caustic soda \| Chlor Alkali Products and Vinyls Segment
Revenue from Contract with Customer, Excluding Assessed Tax [Abstract]
Sales	504.8	405.3
Chlorine, chlorine derivatives and other co-products \| Chlor Alkali Products and Vinyls Segment
Revenue from Contract with Customer, Excluding Assessed Tax [Abstract]
Sales	431.3	431.6
Phenolics and allylics \| Epoxy Segment
Revenue from Contract with Customer, Excluding Assessed Tax [Abstract]
Sales	308.4	299.4
Epoxy resins \| Epoxy Segment
Revenue from Contract with Customer, Excluding Assessed Tax [Abstract]
Sales	294.9	268.2
Commercial \| Winchester Segment
Revenue from Contract with Customer, Excluding Assessed Tax [Abstract]
Sales	111.2	117.9
Military and law enforcement \| Winchester Segment
Revenue from Contract with Customer, Excluding Assessed Tax [Abstract]
Sales	$ 59.7	$ 44.7