RESTRUCTURING CHARGE (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended		17 Months Ended
	Mar. 31, 2012	Mar. 31, 2011	Mar. 31, 2012	Dec. 31, 2011	Dec. 31, 2010	Dec. 09, 2010
RESTRUCTURING CHARGE [Abstract]
Previous mercury cell capacity tonnage at Charleston, TN facility (in tons)						260,000
Membrane capacity tonnage capability at Charleston, TN facility (in tons)						200,000
Estimated capital cost converting Charleston, TN facility	$ 160.0		$ 160.0
Tonnage reduction in chlor alkali manufacturing capacity (in tons)						100,000
Percentage reduction of electricity usage per ECU produced (in hundredths)	25.00%		25.00%
Percentage of capital spending offset provided by State of Mississippi tax incentives (in hundredths)	40.00%		40.00%
Estimated five-year project cost for Winchester relocation	110.0		110.0
Estimated capital spending for Winchester relocation	80.0		80.0
Forecast annual reduction of Winchester's annual operating costs	30.0
Restructuring Cost and Reserve [Line Items]
Restructuring charges	1.9	0.1	46.8
Amounts Utilized	(1.7)
Accrued restructuring costs	12.3	7.1	12.3	12.1	7.0
Inception to date Amounts Utilized (non-cash)			28.3
Inception to date Amounts Utilized (cash)			6.2
Chlor Alkali Products Segment [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring charges	0.3	0.1	31.1
Restructuring And Related Cost Expected Cost	8.0
Winchester Segment [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring charges			15.7
Winchester Relocation [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring charges	1.6	0.1
Restructuring And Related Cost Expected Cost	15.0
Employee severance and job related benefits [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring charges	0.9	0.1	13.3
Amounts Utilized	(0.7)
Accrued restructuring costs	11.5	6.1	11.5	11.3	6.0
Employee severance and job related benefits [Member] | Chlor Alkali Products Segment [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring charges			5.2
Employee severance and job related benefits [Member] | Winchester Segment [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring charges			8.1
Write-off of equipment and facility costs [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring charges			17.5
Write-off of equipment and facility costs [Member] | Chlor Alkali Products Segment [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring charges			17.5
Write-off of equipment and facility costs [Member] | Winchester Segment [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring charges			0
Facility Exit Costs (asset retirement obligations [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring charges	0.2	0	7.9
Amounts Utilized	(0.2)
Accrued restructuring costs	0	0	0	0	0
Facility Exit Costs (asset retirement obligations [Member] | Chlor Alkali Products Segment [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring charges			7.3
Facility Exit Costs (asset retirement obligations [Member] | Winchester Segment [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring charges			0.6
Lease and other contract termination costs [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring charges	0	0	1.0
Amounts Utilized	0
Accrued restructuring costs	0.8	1.0	0.8	0.8	1.0
Lease and other contract termination costs [Member] | Chlor Alkali Products Segment [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring charges			1.0
Lease and other contract termination costs [Member] | Winchester Segment [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring charges			0
Pension and other postretirement benefits curtailment [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring charges			4.1
Pension and other postretirement benefits curtailment [Member] | Chlor Alkali Products Segment [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring charges			0
Pension and other postretirement benefits curtailment [Member] | Winchester Segment [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring charges			4.1
Employee Relocation Cost [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring charges	0.8	0	3.0
Amounts Utilized	(0.8)
Accrued restructuring costs	0	0	0	0	0
Employee Relocation Cost [Member] | Chlor Alkali Products Segment [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring charges			0.1
Employee Relocation Cost [Member] | Winchester Segment [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring charges			$ 2.9