Significant Accounting Policies (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020	Dec. 31, 2020
Contract with Customer, Asset, after Allowance for Credit Loss	$ 11		$ 11		$ 5
Restricted Cash and Cash Equivalents, Current	2		2		4
net allowance for doubtful accounts	3		3		$ 3
Selling, general and administrative expense	90	$ 56	243	$ 164
Depreciation and amortization			148	143
Accounts Receivable, Allowance for Credit Loss, Writeoff	1		1
Insurance premium classification adjustment				13
Other assets, reclassification				13
Impairment charge adjustment		8		8
Effect of Fourth Quarter Events [Line Items]
Net income (Loss), previously reported		(102)		(203)
Net Income (Loss) Attributable to Parent, previously reported		(102)		(203)
(Loss) income from discontinued operations, net of taxes, previously reported		(76)		(79)
Increase (Decrease) in other operating assets, as previously reported				(1)
Net cash provided by (used in) operating activities, continuing operations, previously reported				(11)
Net cash (used in) provided by operating activities from discontinued operations				(1)
Net cash provided by (used in) operating activities, previously reported				(12)
Proceeds from (repayments of) short-term debt, previously reported				(25)
Net cash (used in) provided by financing activities, previously reported				7
Impairment charge adjustment		8		8
Discontinued operations Cash Flow Adjustment				13
Cumulative Operating Activity Adjustment				(13)
Insurance premium classification adjustment				13
Adjustment for asset reclassification on changes in other operating assets				(26)
Cumulative Investing Activity adjustment				13
Net income (loss)	49	(94)	98	(195)
Net Income (Loss) Attributable to Parent	49	(94)	98	(195)
Loss from discontinued operations, net of taxes	$ 0	$ (68)	(5)	(71)
Increase (Decrease) in Other Current Assets				(27)
Net Cash Provided by (Used in) Operating Activities, Continuing Operations			106	(37)
Net cash (used in) provided by operating activities from discontinued operations			(1)	12
Net Cash Provided by (Used in) Operating Activities			105	(25)
Net short-term debt borrowings			(8)	(12)
Net Cash Provided by (Used in) Financing Activities			$ (179)	$ 20

HEXION INC. 10-Q