Document and Entity Information Document - USD ($)	12 Months Ended
	Dec. 31, 2018	Apr. 01, 2019
Document Information [Line Items]
Entity Registrant Name	HEXION INC.
Entity Central Index Key	0000013239
Current Fiscal Year End Date	--12-31
Entity Filer Category	Non-accelerated Filer
Document Type	10-K
Document Period End Date	Dec. 31, 2018
Document Fiscal Year Focus	2018
Document Fiscal Period Focus	Q4
Amendment Flag	false
Entity Common Stock, Shares Outstanding		82,556,847
Entity Well-known Seasoned Issuer	No
Entity Voluntary Filers	Yes
Entity Current Reporting Status	Yes
Entity Emerging Growth Company	false
Entity Small Business	false
Entity Ex Transition Period	false
Entity Shell Company	false
Entity Public Float	$ 0