ACQUISITION (Details) (USD $) In Millions, except Per Share data, unless otherwise specified		3 Months Ended	2 Months Ended	12 Months Ended		12 Months Ended		2 Months Ended	3 Months Ended	12 Months Ended
	Feb. 28, 2011	Mar. 31, 2011 SunBelt [Member]	Feb. 28, 2011 Customers, customer contracts and relationships [Member]	Dec. 31, 2012 Guaranteed Senior Secured Notes due 2017, Series O [Member]	Dec. 22, 1997 Guaranteed Senior Secured Notes due 2017, Series O [Member]	Dec. 31, 2012 Guaranteed Senior Secured Notes due 2017, Series G [Member]	Dec. 22, 1997 Guaranteed Senior Secured Notes due 2017, Series G [Member]	Feb. 28, 2011 SunBelt [Member]	Jun. 30, 2011 SunBelt [Member]	Dec. 31, 2012 SunBelt [Member]
Business Acquisition [Line Items]
PolyOne Corporation's interest in SunBelt (in hundredths)	50.00%
Cash consideration for SunBelt purchase								$ 132.3
Olin's ownership percentage of SunBelt after acquisition of PolyOne's interest (in hundredths)								100.00%
Membrane technology capacity of plant (in tons)								350,000
Earn out agreement term (in years)								three
Cash remitted to PolyOne for distributable cash generated by SunBelt									6.0
Distributable cash non-consolidated affiliate									50.00%
Required annual debt repayment for Series O and Series G notes				6.1		6.1				12.2
Remaining principal balance of consolidated notes								85.3
Previous equity percentage in SunBelt (in hundredths)	50.00%							50.00%
Discrete deferred tax expense relating to the SunBelt acquisition								76.0
Total current assets								37.6
Property, plant and equipment								87.4
Deferred income taxes								0.4
Other assets								5.8
Total assets acquired								131.2
Total current liabilities								42.7
Long-term debt								75.1
Other liabilities								27.6
Total liabilities assumed								145.4
Less Investment in SunBelt								(0.8)
Net liabilities assumed								(13.4)
Liabilities for uncertainties								48.3
Gain on remeasurement of investment in SunBelt								181.4
Goodwill								327.1
Fair value of total consideration								180.6
Cash and cash equivalents								8.9
Current installment of long term debt								12.2
Equity earnings of nonconsolidated affiliate for Sunbelt								6.3
Pretax gain on acquisition of SunBelt								181.4
Fair value of acquired debt								87.3
Debt Instrument [Line Items]
Face amount of senior secured notes					97.5		97.5
Interest rate on SunBelt notes					7.23%		7.23%
Required annual debt repayment for Series O and Series G notes				6.1		6.1				12.2
Finite-Lived Intangible Assets [Line Items]
Final valuation of intangible assets relating to customers, customer contracts and relationships			5.8
Estimated useful life of intangible assets (in years)			15
Tax deductible portion of goodwill	163.7
Pro forma summary of the condensed statements of income as if the Sunbelt acquisition occurred on January 1, 2010 [Abstract]
Sales		462.3
Net income		32.4
Net income per common share basic (in dollars per share)		$ 0.41
Net income per common share diluted (in dollars per share)		$ 0.40
Sunbelt acquisition costs included in Chlor Alkali Products		0.8
Additional amortization expense related to the fair value of acquired identifiable intangible assets		0.1
Reduction of depreciation expense related to the fair value adjustment to property, plant and equipment		1.0
Reduction in interest expense as a result of increasing the carrying value of acquired debt obligations to its estimated fair value		0.1
Additional accretion expense for the earn out liability that was recorded as a result of the acquisition		0.4
Pro forma increase of tax provision due to fair value adjustments		$ 2.5