Note 3 - HSG Transactions (Details Textual) - USD ($) $ in Millions		9 Months Ended
	Sep. 09, 2020	Sep. 30, 2020	Sep. 30, 2021	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2016	Jun. 01, 2016
Cash, Cash Equivalents, Restricted Cash and Restricted Cash Equivalents, Ending Balance		$ 2,514	$ 2,212	$ 2,672	$ 2,434
Stockholders' Equity Attributable to Noncontrolling Interest, Ending Balance			$ 210	$ 191
HSG [Member] | Developed Technologies [Member]
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Intangible Assets, Other than Goodwill, Total	$ 215
Finite-Lived Intangible Asset, Useful Life (Year)	20 years
HSG [Member] | Other Intangible Assets [Member]
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Intangible Assets, Other than Goodwill, Total	$ 70
Finite-Lived Intangible Asset, Useful Life (Year)	15 years
HSG [Member]
Cash, Cash Equivalents, Restricted Cash and Restricted Cash Equivalents, Ending Balance	$ 75
Debt Instrument, Face Amount	175
Stockholders' Equity Attributable to Noncontrolling Interest, Ending Balance	102
HSG [Member] | DuPont de Nemours, Inc [Member]
Noncontrolling Interest, Increase from Redemptions or Purchase of Interests	250
Duponts Trichlorosilane [Member] | HSG [Member]
Business Combination, Consideration Transferred, Total	255
Business Combination, Assets Arising from Contingencies, Amount Recognized	175
Business Acquisition, Preacquisition Contingency, Amount of Settlement	$ 200
Settlement Term (Year)	3 years
Settlement Annual Payment	$ 58
Hemlock Semiconductor LLC [Member]
Business Acquisition, Percentage of Voting Interests Acquired	100.00%
Hemlock Semiconductor Operations LLC [Member]
Business Combination, Consideration Transferred, Total	$ 352
Business Combination, Assets Arising from Contingencies, Amount Recognized	$ 20
Business Acquisition, Percentage of Voting Interests Acquired	80.50%
Dow Corning Corporation [Member]
Equity Method Investment, Ownership Percentage						50.00%	50.00%
Hemlock Semiconductor LLC [Member]
Equity Method Investment, Ownership Percentage						49.90%
Hemlock Semiconductor Operations LLC [Member]
Equity Method Investment, Ownership Percentage						40.25%
HSG [Member]
Redeemable Noncontrolling Interest, Equity, Redemption Value, Total	$ 250
HSG [Member] | TCS Settlement [Member]
Gain (Loss) Related to Litigation Settlement, Total		$ (81)