RESTRUCTURING CHARGES (Details 1) $ in Millions	3 Months Ended				6 Months Ended		39 Months Ended	55 Months Ended
	Jun. 30, 2019 USD ($)	Mar. 31, 2019 USD ($)	Jun. 30, 2018 USD ($)	Mar. 31, 2018 USD ($)	Jun. 30, 2019 USD ($)	Jun. 30, 2018 USD ($)	Jun. 30, 2019 USD ($)	Jun. 30, 2019 USD ($)	Dec. 31, 2018 USD ($)	Dec. 31, 2017 USD ($)	Mar. 21, 2016 T
Restructuring Cost and Reserve [Line Items]
Restructuring charges	$ 3.8	$ 4.0	$ 6.4	$ 4.0	$ 7.8	$ 10.4		$ 189.8
Inception to date Amounts Utilized (cash)								99.0
Inception to date Amounts Utilized (non-cash)								84.6
Accrued restructuring costs	6.2		8.1		6.2	8.1	$ 6.2	6.2	$ 8.2	$ 5.1
Geelong | Winchester
Restructuring Cost and Reserve [Line Items]
Restructuring charges	0.2				0.3
Additional restructuring and related expected cost	1.0				1.0		1.0	1.0
Other Winchester | Winchester
Restructuring Cost and Reserve [Line Items]
Restructuring charges					1.4
Capacity Reductions | Chlor Alkali Products and Vinyls
Restructuring Cost and Reserve [Line Items]
Total Product Segment Production Capacity Decrease | T											433,000
Henderson Product Segment Production Capacity Decrease | T											153,000
Niagara Product Segment Production Capacity | T											300,000
Reduced Niagara Segment Production Capacity | T											240,000
Freeport Product Segment Production Capacity Decrease | T											220,000
Restructuring charges	3.6		6.1		6.1	9.1	165.8
Additional restructuring and related expected cost	10.0				10.0		10.0	10.0
Becancour | Chlor Alkali Products and Vinyls
Restructuring Cost and Reserve [Line Items]
Restructuring charges			$ 0.3			$ 1.3		18.2
Additional restructuring and related expected cost	$ 1.0				$ 1.0		$ 1.0	$ 1.0