Restructuring and related activities (2020 Restructuring Program) (Details) - USD ($) $ in Millions	3 Months Ended					6 Months Ended		10 Months Ended
	Jun. 30, 2021	Mar. 31, 2021	Dec. 31, 2020	Sep. 30, 2020	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021
Restructuring Cost and Reserve [Line Items]
Restructuring Charges	$ 43				$ 6	$ 53	$ 102
Packaging & Specialty Plastics [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring Charges	8				6	8	12
Industrial Intermediates & Infrastructure [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring Charges	1				0	1	0
Performance Materials & Coatings [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring Charges	10				0	10	0
Corporate Segment [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring Charges	24				$ 0	34	$ 90
2020 Restructuring Program [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring Charges				$ 575				$ 595
Restructuring Reserve, Settled without Cash	(12)		$ (4)	(197)
Payments for Restructuring	56	$ 49	7	1
Restructuring Reserve	269	315	364	377		269		$ 269
Restructuring and asset related charges - net	$ 22		(2)			$ 22
2020 Restructuring Program [Member] | The Dow Chemical Company
Restructuring Cost and Reserve [Line Items]
restructuring and related cost, percentage	6.00%					6.00%		6.00%
2020 Restructuring Program [Member] | Accrued and Other Current Liabilities [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring Reserve	$ 197		227			$ 197		$ 197
2020 Restructuring Program [Member] | Other Noncurrent Obligations [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring Reserve	72		137			72		72
2020 Restructuring Program [Member] | Packaging & Specialty Plastics [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring Charges				11
Restructuring and asset related charges - net	8
2020 Restructuring Program [Member] | Industrial Intermediates & Infrastructure [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring Charges				22
Restructuring and asset related charges - net	1
2020 Restructuring Program [Member] | Performance Materials & Coatings [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring Charges				174
Restructuring and asset related charges - net	10		3
2020 Restructuring Program [Member] | Corporate Segment [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring Charges				368
Restructuring and asset related charges - net	3		(5)
Employee Severance [Member] | 2020 Restructuring Program [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring Charges				297				297
Restructuring Reserve, Settled without Cash	0		0	0
Payments for Restructuring	53	37	7	1
Restructuring Reserve	199	252	289	296		199		199
Restructuring and asset related charges - net	0		0
Employee Severance [Member] | 2020 Restructuring Program [Member] | Packaging & Specialty Plastics [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring Charges				0
Restructuring and asset related charges - net	0
Employee Severance [Member] | 2020 Restructuring Program [Member] | Industrial Intermediates & Infrastructure [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring Charges				0
Restructuring and asset related charges - net	0
Employee Severance [Member] | 2020 Restructuring Program [Member] | Performance Materials & Coatings [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring Charges				0
Restructuring and asset related charges - net	0		0
Employee Severance [Member] | 2020 Restructuring Program [Member] | Corporate Segment [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring Charges				297
Restructuring and asset related charges - net	0		0
Asset write-downs and write-offs [Member] | 2020 Restructuring Program [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring Charges				197				208
Restructuring Reserve, Settled without Cash	(12)		(1)	(197)
Payments for Restructuring	0	0	0	0
Restructuring Reserve	0	0	0	0		0		0
Restructuring and asset related charges - net	12		(1)
Asset write-downs and write-offs [Member] | 2020 Restructuring Program [Member] | Packaging & Specialty Plastics [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring Charges				11
Restructuring and asset related charges - net	0
Asset write-downs and write-offs [Member] | 2020 Restructuring Program [Member] | Industrial Intermediates & Infrastructure [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring Charges				22
Restructuring and asset related charges - net	1
Asset write-downs and write-offs [Member] | 2020 Restructuring Program [Member] | Performance Materials & Coatings [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring Charges				117
Restructuring and asset related charges - net	8		(1)
Asset write-downs and write-offs [Member] | 2020 Restructuring Program [Member] | Corporate Segment [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring Charges				47
Restructuring and asset related charges - net	3		0
Costs Associated with Exit and Disposal Activities [Member] | 2020 Restructuring Program [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring Charges				81				90
Restructuring Reserve, Settled without Cash	0		(5)	0
Payments for Restructuring	3	12	0	0
Restructuring Reserve	70	$ 63	75	81		$ 70		$ 70
Restructuring and asset related charges - net	10		(1)
Costs Associated with Exit and Disposal Activities [Member] | 2020 Restructuring Program [Member] | Packaging & Specialty Plastics [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring Charges				0
Restructuring and asset related charges - net	8
Costs Associated with Exit and Disposal Activities [Member] | 2020 Restructuring Program [Member] | Industrial Intermediates & Infrastructure [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring Charges				0
Restructuring and asset related charges - net	0
Costs Associated with Exit and Disposal Activities [Member] | 2020 Restructuring Program [Member] | Performance Materials & Coatings [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring Charges				57
Restructuring and asset related charges - net	2		4
Costs Associated with Exit and Disposal Activities [Member] | 2020 Restructuring Program [Member] | Corporate Segment [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring Charges				$ 24
Restructuring and asset related charges - net	$ 0		$ (5)