Segment Information (Details) - Reconciliation of Segment EBITDA to Net Income - USD ($) $ in Millions		3 Months Ended		6 Months Ended	9 Months Ended	12 Months Ended
	Jul. 01, 2019	Sep. 30, 2019	Sep. 30, 2018	Jun. 30, 2019	Sep. 30, 2018	Dec. 31, 2018
Segment Reporting Information [Line Items]
Reorganization items, net of non-cash inventory step--up	$ (3,232)	$ 0	$ 0	$ (3,076)	$ 0
Non-cash impact of Inventory step-up	(29)	29	0	(29)	0
Net (loss) income attributable to Hexion Inc.	3,054	(43)	(18)	2,894	(53)
Net income attributable to noncontrolling interest	0	0	0	1	1
Net (loss) income	3,054	(43)	(18)	2,895	(52)
Income tax (benefit) expense	207	(4)	6	222	17	$ 40
Interest expense, net	0	28	83	89	250
Depreciation and amortization	0	55	27	52	85
Non-cash asset impairments	0	0		0	30
accelerated depreciation			2		2
EBITDA	3,261	36	100	3,258	302
Other Asset Impairment Charges	0	0	7	0	32
Business realignment costs	0	13	5	15	19
Gain on disposition	0	0	0	0	(44)
Professional Fees	0	5	4	26	10
Realized and unrealized foreign currency losses (gains)	0	9	4	(6)	26
Other (3)	18	7	8	45	29
Total adjustments	(3,243)	63	28	(3,025)	72
Segment EBITDA	18	99	128	233	374
Epoxy, Phenolic and Coating Resins
Segment Reporting Information [Line Items]
Segment EBITDA	0	50	66	111	208
Forest Products Resins
Segment Reporting Information [Line Items]
Segment EBITDA	18	66	76	152	219
Corporate and Other [Member]
Segment Reporting Information [Line Items]
Segment EBITDA	$ 0	$ (17)	$ (14)	$ (30)	$ (53)