REVERSE MORRIS TRUST TRANSACTION Reverse Morris Trust (Details) - USD ($) $ in Millions		3 Months Ended	9 Months Ended	12 Months Ended
	Oct. 05, 2015	Dec. 31, 2015	Sep. 30, 2015	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Extinguishment of Debt, Amount	$ 1,161
Gain (Loss) on Extinguishment of Debt	$ (68)			$ 0	$ 0	$ (8)
Number of Splitco shares exchanged	100,000,000
Conversion Factor, number of Olin Shares for each share of Splitco	0.87482759
Number of Olin shares distributed in share exchange	87,500,000
Shareholder Ownership Percentage in Olin	52.70%
Deferred Revenue				524
Disposal Group,Including Discontinued Operation, Nonrecurring Transaction Costs				0	41	119
Chlorine Value Chain [Domain] | Disposal Group, Disposed of by Means Other than Sale, Not Discontinued Operations [Member]
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Debt Instrument, Fair Value Exchange Amount	$ 1,154
Extinguishment of Debt, Amount	1,161
Gain (Loss) on Extinguishment of Debt	(68)
Increase in Treasury Stock from Share Exchange, Noncash	$ 1,523
Percent reduction in outstanding shares	3.00%
Proceeds from Issuance of Debt	$ 875
Deferred Revenue	434
Deferred Revenue, Current	16
Deferred Revenue, Noncurrent	418
Disposal Group, Including Discontinued Operation, Pension Plan Benefit Obligation	439
Disposal Group, Including Discontinued Operation, Consideration		$ 3,510				3,510
Disposal Group, Not Discontinued Operation, Gain (Loss) on Disposal		2,233		$ 7	6	2,233
Disposal Group Not Discontinued Operation Gain (Loss) On Disposal After Tax		$ 2,215
Income Before Income Taxes 2			$ 139
Loss before income taxes attributable to noncontrolling interests			11
Income Before Income Taxes attributable to The Dow Chemical Company 2			$ 150
Disposal Group,Including Discontinued Operation, Nonrecurring Transaction Costs						$ 119
Pension Plan [Member] | Chlorine Value Chain [Domain] | Disposal Group, Disposed of by Means Other than Sale, Not Discontinued Operations [Member]
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Disposal Group, Not Discontinued Operation, Gain (Loss) on Disposal					$ 5
SplitCo [Member] | Chlorine Value Chain [Domain] | Disposal Group, Disposed of by Means Other than Sale, Not Discontinued Operations [Member]
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Financing Receivable, Net	$ 1,220
Common Stock [Member] | Chlorine Value Chain [Domain] | Disposal Group, Disposed of by Means Other than Sale, Not Discontinued Operations [Member]
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Dow Shares Exchange in Share Exchange Offer	34,100,000
Chlor-Alkali joint venture [Member]
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Business Acquisition, Percentage of Voting Interests Acquired	50.00%
Payments to Acquire Businesses, Gross	$ 133
Loss on purchase of Redeemable Noncontrolling Interest included in disposal group	$ 25