SUPPLEMENTARY INFORMATION (Sundry Income, Net) - USD ($) $ in Millions	3 Months Ended				12 Months Ended
	Dec. 31, 2020	Sep. 30, 2020	Jun. 30, 2020	Sep. 30, 2019	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Supplementary Information [Line Items]
Non-operating pension and other postretirement benefit plan net credit					$ 103	$ 205	$ 123
Foreign exchange gains (losses)					(62)	91	(119)
Gain (loss) on divestiture					717	(49)
Loss on early extinguishment of debt					(149)	(102)	(54)
Gain (loss) related to litigation settlement					544	205
Gain (Loss) on Disposition of Other Assets					48	67	18
Charges related to separation, distribution and tax matters agreements					(21)	(144)
Other - net					84	113	128
Sundry income (expense) - net					1,269	461	96
Dow Silicones Corporation
Supplementary Information [Line Items]
Gain and post-close adjustments related to Dow Silicones ownership restructure					0	0	(20)
Commercial Creditors Litigation
Supplementary Information [Line Items]
Loss Contingency Accrual, Period Increase (Decrease)					0	(50)	0
Dow V. Nova Chemicals Corporation Ethylene Asset Matter [Member] [Member]
Supplementary Information [Line Items]
Gain (loss) related to litigation settlement	$ 552		$ 18	$ 186
MEGlobal
Supplementary Information [Line Items]
Gain (loss) on divestiture							20
MEGlobal | Disposal Group, Disposed of by Sale, Not Discontinued Operations
Supplementary Information [Line Items]
Gain (loss) on divestiture					0	0	20
Marine and Terminal Operations and Assets
Supplementary Information [Line Items]
Gain (loss) on divestiture					499
Nonoperating Income (Expense)
Supplementary Information [Line Items]
Gain (loss) on divestiture					(15)	(49)	0
Charges related to separation, distribution and tax matters agreements					(21)	(69)	0
Nonoperating Income (Expense) | Breast Implant and Other Products Liability Claims
Supplementary Information [Line Items]
Loss Contingency Accrual, Period Increase (Decrease)					(5)	(85)	0
Nonoperating Income (Expense) | Dow V. Nova Chemicals Corporation Ethylene Asset Matter [Member] [Member]
Supplementary Information [Line Items]
Gain (loss) related to litigation settlement					544	170	0
Nonoperating Income (Expense) | Rail Infrastructure [Member]
Supplementary Information [Line Items]
Gain (loss) on divestiture					499	0	0
Nonoperating Income (Expense) | Marine and Terminal Operations and Assets
Supplementary Information [Line Items]
Gain (loss) on divestiture					233	0	0
Dow Silicones Corporation | Breast Implant and Other Products Liability Claims
Supplementary Information [Line Items]
Loss Contingency Accrual, Period Increase (Decrease)		$ 98
Dow Silicones Corporation | Commercial Creditors Litigation
Supplementary Information [Line Items]
Loss Contingency Accrual, Period Increase (Decrease)		$ (50)
The Dow Chemical Company
Supplementary Information [Line Items]
Non-operating pension and other postretirement benefit plan net credit					103	205	123
Foreign exchange gains (losses)					(65)	77	(119)
Loss on early extinguishment of debt					(149)	(102)	(54)
Gain (Loss) on Disposition of Other Assets					48	67	18
Other - net					82	113	128
Sundry income (expense) - net					1,274	573	96
The Dow Chemical Company | Dow Silicones Corporation
Supplementary Information [Line Items]
Gain and post-close adjustments related to Dow Silicones ownership restructure					0	0	(20)
The Dow Chemical Company | Commercial Creditors Litigation
Supplementary Information [Line Items]
Loss Contingency Accrual, Period Increase (Decrease)					0	(50)	0
The Dow Chemical Company | MEGlobal | Disposal Group, Disposed of by Sale, Not Discontinued Operations
Supplementary Information [Line Items]
Gain (loss) on divestiture					0	0	20
The Dow Chemical Company | Nonoperating Income (Expense)
Supplementary Information [Line Items]
Gain (loss) on divestiture					(15)	2	0
Charges related to separation, distribution and tax matters agreements					(11)	6	0
The Dow Chemical Company | Nonoperating Income (Expense) | Breast Implant and Other Products Liability Claims
Supplementary Information [Line Items]
Loss Contingency Accrual, Period Increase (Decrease)					(5)	(85)	0
The Dow Chemical Company | Nonoperating Income (Expense) | Dow V. Nova Chemicals Corporation Ethylene Asset Matter [Member] [Member]
Supplementary Information [Line Items]
Gain (loss) related to litigation settlement					544	170	0
The Dow Chemical Company | Nonoperating Income (Expense) | Rail Infrastructure [Member]
Supplementary Information [Line Items]
Gain (loss) on divestiture					499	0	0
The Dow Chemical Company | Nonoperating Income (Expense) | Marine and Terminal Operations and Assets
Supplementary Information [Line Items]
Gain (loss) on divestiture					$ 233	$ 0	$ 0