The estimated net amount of existing gains or losses on cash flow hedges at the reporting date expected to be reclassified to earnings within the next 12 months.

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 815
-SubTopic 30
-Section 50
-Paragraph 1
-Subparagraph (c)
-URI http://asc.fasb.org/extlink&oid=121549185&loc=d3e80748-113994

+ Details

Name:	us-gaap_CashFlowHedgeGainLossToBeReclassifiedWithinTwelveMonths
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

Net fair value of all derivative instruments designated as cash flow hedging instruments, which is ordinarily reflected within other comprehensive income.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 815
-SubTopic 10
-Section 45
-Paragraph 5
-URI http://asc.fasb.org/extlink&oid=117331979&loc=d3e41228-113958

+ Details

Name:	us-gaap_CashFlowHedgesDerivativeInstrumentsAtFairValueNet
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Amount of increase (decrease) in the fair value of derivatives recognized in the income statement.

+ References

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 815
-SubTopic 10
-Section 50
-Paragraph 4A
-Subparagraph (b)(1)
-URI http://asc.fasb.org/extlink&oid=121590274&loc=SL5618551-113959

+ Details

Name:	us-gaap_DerivativeGainLossOnDerivativeNet
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

+ References

No definition available.

+ Details

Name:	us-gaap_DerivativeLineItems
Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Definition

Nominal or face amount used to calculate payment on derivative.

+ References

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 815
-SubTopic 10
-Section 50
-Paragraph 1B
-URI http://asc.fasb.org/extlink&oid=121590274&loc=SL5580258-113959

Reference 2: http://www.xbrl.org/2009/role/commonPracticeRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 815
-SubTopic 10
-Section 50
-Paragraph 1A
-Subparagraph (d)
-URI http://asc.fasb.org/extlink&oid=121590274&loc=SL5579245-113959

+ Details

Name:	us-gaap_DerivativeNotionalAmount
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	na
Period Type:	instant

- Definition

The amount of net gains or losses on interest rate cash flow hedges reclassified during the period to earnings from accumulated other comprehensive income upon the hedged transaction affecting earnings.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 815
-SubTopic 10
-Section 50
-Paragraph 4C
-Subparagraph (c)
-URI http://asc.fasb.org/extlink&oid=121590274&loc=SL5624171-113959

+ Details

Name:	us-gaap_InterestRateCashFlowHedgeGainLossReclassifiedToEarningsNet
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Details

Name:	us-gaap_DerivativeInstrumentRiskAxis=us-gaap_ForwardContractsMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_DerivativeInstrumentRiskAxis=oln_ForwardContractsSellMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_DerivativeInstrumentRiskAxis=us-gaap_CommodityContractMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_DerivativeInstrumentRiskAxis=us-gaap_InterestRateContractMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_DerivativeInstrumentRiskAxis=oln_FixedInterestRateSwaps1100MTranche1Member
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_DerivativeInstrumentRiskAxis=oln_FixedInterestRateSwaps900MTranche2Member
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_DerivativeInstrumentRiskAxis=oln_FixedInterestRateSwaps400MTranche3Member
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_DerivativeInstrumentRiskAxis=oln_InterestRateSwapsDesignatedAsFairValueHedgesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

DERIVATIVE FINANCIAL INSTRUMENTS (Details Textuals) - USD ($) $ in Millions	3 Months Ended	6 Months Ended
	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019	Dec. 31, 2019	Oct. 31, 2016	Jun. 30, 2016	Apr. 30, 2016
Derivative [Line Items]
Notional amount	$ 186.1	$ 225.1	$ 186.1	$ 174.6
Forward Contracts
Derivative [Line Items]
Notional amount	130.8	176.6	130.8	140.6
Forward Contracts Sell
Derivative [Line Items]
Notional amount	120.5	111.7	120.5	$ 99.2
Commodity Contract
Derivative [Line Items]
Cash Flow Hedges Derivative Instruments at Fair Value, Net		(1.9)
Cash Flow Hedge Gain (Loss) to be Reclassified within Twelve Months		$ (3.1)
Interest Rate Contract
Derivative [Line Items]
Interest Rate Cash Flow Hedge Gain (Loss) Reclassified to Earnings, Net	1.2		2.5
Fixed Interest Rate Swaps $1,100M (Tranche 1)
Derivative [Line Items]
Notional amount							$ 1,100.0
Fixed Interest Rate Swaps $900M (Tranche 2)
Derivative [Line Items]
Notional amount							900.0
Fixed Interest Rate Swaps $400M (Tranche 3)
Derivative [Line Items]
Notional amount							$ 400.0
Interest Rate Swaps Designated As Fair Value Hedges
Derivative [Line Items]
Notional amount	500.0		500.0		$ 250.0	$ 250.0
Amount of Gain (Loss)	$ (1.0)		$ (1.7)