ACCOUNTING POLICIES (Details) - USD ($) $ in Millions		3 Months Ended
Jan. 01, 2019	Mar. 31, 2019
Accounting Policies [Abstract]
Lease accounting adoption asset and liability	$ 291.9
Lease accounting adoption adjustment	$ 11.2	$ 11.2

Lease accounting adoption adjustment gain resulting from the application of ASU 2016-02 related to ASC 842, Leases. Amount represents the amount directly credited to retained earnings as a result of the application of the new standard.

No definition available.

Name:	oln_Leaseaccountingadoptionadjustment
Namespace Prefix:	oln_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration