Restructuring and related activities (2020 Restructuring Program) (Details) - USD ($) $ in Millions	3 Months Ended					9 Months Ended		13 Months Ended
	Sep. 30, 2021	Jun. 30, 2021	Mar. 31, 2021	Dec. 31, 2020	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021
Restructuring Cost and Reserve [Line Items]
Restructuring and asset related charges - net	$ 0				$ 617	$ 22	$ 719
Restructuring Charges	16				617	69	719
The Dow Chemical Company
Restructuring Cost and Reserve [Line Items]
Restructuring and asset related charges - net	0				617	22	719
Packaging & Specialty Plastics [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring Charges	0				18	8	30
Industrial Intermediates & Infrastructure [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring Charges	0				22	1	22
Performance Materials & Coatings [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring Charges	0				189	10	189
Corporate Segment [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring Charges	16				388	50	478
2020 Restructuring Program [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring and asset related charges - net		$ 22		$ (2)
Restructuring Charges					575			$ 595
Restructuring Reserve, Settled without Cash		(12)		(4)	(197)
Payments for Restructuring	57	56	$ 49	7	1
Restructuring Reserve	$ 212	269	315	364	377	$ 212	377	$ 212
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	$ 147			227		$ 147		$ 147
2020 Restructuring Program [Member] | Other Noncurrent Obligations [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring Reserve	65			137		65		65
2020 Restructuring Program [Member] | Packaging & Specialty Plastics [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring and asset related charges - net		8
Restructuring Charges					11
2020 Restructuring Program [Member] | Industrial Intermediates & Infrastructure [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring and asset related charges - net		1
Restructuring Charges					22
2020 Restructuring Program [Member] | Performance Materials & Coatings [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring and asset related charges - net		10		3
Restructuring Charges					174
2020 Restructuring Program [Member] | Corporate Segment [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring and asset related charges - net		3		(5)
Restructuring Charges					368
Employee Severance [Member] | 2020 Restructuring Program [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring and asset related charges - net		0		0
Restructuring Charges					297			297
Restructuring Reserve, Settled without Cash		0		0	0
Payments for Restructuring	55	53	37	7	1
Restructuring Reserve	144	199	252	289	296	144	296	144
Employee Severance [Member] | 2020 Restructuring Program [Member] | Packaging & Specialty Plastics [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring and asset related charges - net		0
Restructuring Charges					0
Employee Severance [Member] | 2020 Restructuring Program [Member] | Industrial Intermediates & Infrastructure [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring and asset related charges - net		0
Restructuring Charges					0
Employee Severance [Member] | 2020 Restructuring Program [Member] | Performance Materials & Coatings [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring and asset related charges - net		0		0
Restructuring Charges					0
Employee Severance [Member] | 2020 Restructuring Program [Member] | Corporate Segment [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring and asset related charges - net		0		0
Restructuring Charges					297
Asset write-downs and write-offs [Member] | 2020 Restructuring Program [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring and asset related charges - net		12		(1)
Restructuring Charges					197			208
Restructuring Reserve, Settled without Cash		(12)		(1)	(197)
Payments for Restructuring	0	0	0	0	0
Restructuring Reserve	0	0	0	0	0	0	0	0
Asset write-downs and write-offs [Member] | 2020 Restructuring Program [Member] | Packaging & Specialty Plastics [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring and asset related charges - net		0
Restructuring Charges					11
Asset write-downs and write-offs [Member] | 2020 Restructuring Program [Member] | Industrial Intermediates & Infrastructure [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring and asset related charges - net		1
Restructuring Charges					22
Asset write-downs and write-offs [Member] | 2020 Restructuring Program [Member] | Performance Materials & Coatings [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring and asset related charges - net		8		(1)
Restructuring Charges					117
Asset write-downs and write-offs [Member] | 2020 Restructuring Program [Member] | Corporate Segment [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring and asset related charges - net		3		0
Restructuring Charges					47
Costs Associated with Exit and Disposal Activities [Member] | 2020 Restructuring Program [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring and asset related charges - net		10		(1)
Restructuring Charges					81			90
Restructuring Reserve, Settled without Cash		0		(5)	0
Payments for Restructuring	2	3	12	0	0
Restructuring Reserve	$ 68	70	$ 63	75	81	$ 68	$ 81	$ 68
Costs Associated with Exit and Disposal Activities [Member] | 2020 Restructuring Program [Member] | Packaging & Specialty Plastics [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring and asset related charges - net		8
Restructuring Charges					0
Costs Associated with Exit and Disposal Activities [Member] | 2020 Restructuring Program [Member] | Industrial Intermediates & Infrastructure [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring and asset related charges - net		0
Restructuring Charges					0
Costs Associated with Exit and Disposal Activities [Member] | 2020 Restructuring Program [Member] | Performance Materials & Coatings [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring and asset related charges - net		2		4
Restructuring Charges					57
Costs Associated with Exit and Disposal Activities [Member] | 2020 Restructuring Program [Member] | Corporate Segment [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring and asset related charges - net		$ 0		$ (5)
Restructuring Charges					$ 24