Document - Cover - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Mar. 01, 2021
Document Information [Line Items]
Document Type	10-K
Document Annual Report	true
Document Transition Report	false
Entity Registrant Name	HEXION INC.
Entity Central Index Key	0000013239
Current Fiscal Year End Date	--12-31
Entity Filer Category	Non-accelerated Filer
Document Period End Date	Dec. 31, 2020
Document Fiscal Year Focus	2020
Document Fiscal Period Focus	FY
Entity Incorporation, State or Country Code	NJ
Entity Tax Identification Number	13-0511250
Entity Address, Address Line One	180 East Broad St.,
Entity Address, City or Town	Columbus,
Entity Address, State or Province	OH
Entity Address, Postal Zip Code	43215
City Area Code	614
Local Phone Number	225-4000
Amendment Flag	false
Entity Small Business	false
Entity Emerging Growth Company	false
Entity Shell Company	false
Entity Current Reporting Status	No
Entity File Number	1-71
Entity Interactive Data Current	Yes
Entity Common Stock, Shares Outstanding		100
Entity Well-known Seasoned Issuer	No
Entity Voluntary Filers	Yes
Entity Public Float	$ 0