Income Taxes Income Taxes - Geographic Allocation of Income and Provision for Income Taxes (Details) - USD ($) $ in Millions	3 Months Ended															12 Months Ended
	Dec. 31, 2020	[1]	Sep. 30, 2020	Jun. 30, 2020	[2]	Mar. 31, 2020	[3],[4]	Dec. 31, 2019	[5]	Sep. 30, 2019	[6],[7]	Jun. 30, 2019	[8]	Mar. 31, 2019	[9]	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Loss from Continuing Operations before Income Taxes																$ 675	$ (316)	$ (6,806)
Benefit from income taxes on continuing operations																(81)	(46)	(31)
(Loss) income from continuing operations after income taxes	$ 99		$ (390)	$ 766		$ 281		$ (42)		$ (527)		$ 483		$ (184)		756	(270)	(6,775)
Continuing Operations [Member]
Loss from Continuing Operations before Income Taxes, Domestic																(83)	(1,352)	(5,040)
Income (Loss) from Continuing Operations before Income Taxes, Foreign																758	1,036	(1,766)
Loss from Continuing Operations before Income Taxes																675	(316)	(6,806)
Current Federal Tax (Benefit) Expense																28	(11)	(112)
Current State and Local Tax Expense (Benefit)																9	1	(32)
Current Foreign Tax Expense																222	317	446
Total current tax expense (benefit)																259	307	302
Deferred Federal Income Tax (Benefit) Expense																(116)	(392)	(124)
Deferred State and Local Income Tax Expense (Benefit)																27	156	(39)
Deferred Foreign Income Tax Benefit																(251)	(117)	(170)
Total deferred tax expense (benefit)																(340)	(353)	(333)
Benefit from income taxes on continuing operations																(81)	(46)	(31)
(Loss) income from continuing operations after income taxes																$ 756	$ (270)	$ (6,775)

[1] Fourth quarter 2020 includes an after-tax benefit of $(182) million related to Swiss Tax Reform. See Note 10 - Income Taxes, to the Consolidated Financial Statements, for additional information.

[2] Second quarter 2020 includes an after-tax benefit of $(29) million due to an elective change in accounting method that alters the 2019 impact of the business separation on the 2017 Tax Cuts and Jobs Act's foreign tax provision. See Note 10 - Income Taxes, to the Consolidated Financial Statements for additional information.

[3] First quarter 2020 includes a $19 million after tax charge related to the impact of a state tax valuation allowance in the U.S. based on a change in judgment about the realizability of a deferred tax asset. See Note 10 - Income Taxes, to the Consolidated Financial Statements, for additional information.

[4] First quarter 2020 includes a loss of $(53) million recorded in other income - net related to the expected sale of the La Porte site, for which the company signed an agreement during the first quarter 2020.

[5] Fourth quarter 2019 includes a tax benefit of $(34) million related to the impact of the release of a tax valuation allowance recorded against the net deferred tax asset position of a Switzerland legal entity. See Note 10 - Income Taxes, to the Consolidated Financial Statements for additional information.

[6] Third quarter 2019 includes a $33 million charge included in other income (expense) - net associated with remeasuring the company’s Argentine Peso net monetary assets, resulting from an unexpected August primary election result in Argentina. 

[7] Third quarter 2019 includes a tax benefit of $(38) million related to Swiss Tax Reform. See Note 10 - Income Taxes, to the Consolidated Financial Statements for additional information.

[8] Includes a loss on early extinguishment of debt of $(13) million in the second quarter of 2019 related to the retirement of some of the company's debt. See Note 17 - Long-Term Debt and Available Credit Facilities, to the Consolidated Financial Statements for additional information.

[9] First quarter 2019 includes a $(24) million loss recorded in other income (expense) - net related to Historical Dow’s sale of a joint venture related to synergy actions.