ACQUISITION (Details) (USD $) In Millions, except Per Share data, unless otherwise specified	12 Months Ended				12 Months Ended			2 Months Ended	3 Months Ended	12 Months Ended			12 Months Ended
	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009	Feb. 28, 2011	Dec. 31, 2011 SunBelt [Member]	Dec. 31, 2010 SunBelt [Member]	Dec. 31, 2009 SunBelt [Member]	Feb. 28, 2011 SunBelt [Member]	Jun. 30, 2011 SunBelt [Member]	Dec. 31, 2011 SunBelt [Member]	Dec. 31, 2011 Guaranteed Senior Secured Notes Due 2017 Series O [Member]	Dec. 22, 1997 Guaranteed Senior Secured Notes Due 2017 Series O [Member]	Dec. 31, 2011 Guaranteed Senior Secured Notes Due 2017 Series G [Member]	Dec. 22, 1997 Guaranteed Senior Secured Notes Due 2017 Series G [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								350,000
Earn out agreement term (in years)								3
Cash remitted to PolyOne for distributable cash generated by SunBelt									6.0
Distributable cash non-consolidated affiliate (in hundreths)									50.00%
Required annual debt repayment for Series O and Series G notes										12.2	6.1		6.1
Remaining principal balance of consolidated notes								85.3
Previous equity percentage in Sunbelt (in hundredths)				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	27.6	25.9						(0.8)
Net liabilities assumed								(13.4)
Liabilities for uncertainties								48.3
Gain on remeasurement of investment in SunBelt	181.4							181.4
Goodwill								327.1
Fair value of assets acquired								180.6
Cash and cash equivalents								8.9
Current installment of long-term debt								12.2
Pretax gain on acquisition of SunBelt	181.4							181.4
Face amount of senior secured notes												97.5		97.5
Interest rate												7.23%		7.23%
Fair value of acquired debt								87.3
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
SunBelt sales										170.5
SunBelt pretax income										27.2
Expense for earnout liability	6.7
Total earnings of non-consolidated affiliates	9.6	29.9	37.7					6.3
Segment Reporting Information [Line Items]
SunBelt pretax income included in Chlor Alkali Products					38.7
Sunbelt acquisition costs					0.8
SunBelt interest expense					4.0
Sales					1,987.4	1,743.2	1,698.9
Net income					140.6	80.4	154.7
Net income per common share basic (in dollars per share)					$ 1.76	$ 1.02	$ 1.98
Net income per common share diluted (in dollars per share)					$ 1.74	$ 1.01	$ 1.98
Additional amortization expense related to the fair value of acquired identifiable intangible assets					0.1	0.3	0.3
Reduction of depreciation expense related to the fair value adjustment to property, plant and equipment					1.0	5.8	5.9
Reduction in interest expense as a result of increasing the carrying value of acquired debt obligations to its estimated fair value					0.1	0.5	0.5
Additional accretion expense for the earn out liability that was recorded as a result of the acquisition					0.4	2.7	2.7
Pro forma increase of tax provision due to fair value adjustments					$ 2.3	$ 7.3	$ 10.6