Revenue - Disaggregation of Revenue (Details) - USD ($) $ in Millions		12 Months Ended
		Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2017
Disaggregation Of Revenue [Line Items]
Sales		$ 2,493	$ 2,589	$ 2,309
Specialty Ingredients [Member]
Disaggregation Of Revenue [Line Items]
Sales		2,382	2,470	2,216
Intermediates and Solvents [Member]
Disaggregation Of Revenue [Line Items]
Sales		111	119	93
North America [Member] | Specialty Ingredients [Member]
Disaggregation Of Revenue [Line Items]
Sales		945	988	883
North America [Member] | Intermediates and Solvents [Member]
Disaggregation Of Revenue [Line Items]
Sales		58	58	34
Europe [Member] | Specialty Ingredients [Member]
Disaggregation Of Revenue [Line Items]
Sales		779	806	683
Europe [Member] | Intermediates and Solvents [Member]
Disaggregation Of Revenue [Line Items]
Sales		23	24	21
Asia Pacific [Member] | Specialty Ingredients [Member]
Disaggregation Of Revenue [Line Items]
Sales		458	454	432
Asia Pacific [Member] | Intermediates and Solvents [Member]
Disaggregation Of Revenue [Line Items]
Sales		25	31	32
Latin America & Other [Member] | Specialty Ingredients [Member]
Disaggregation Of Revenue [Line Items]
Sales		200	222	218
Latin America & Other [Member] | Intermediates and Solvents [Member]
Disaggregation Of Revenue [Line Items]
Sales		5	6	6
Cellulosics [Member] | Specialty Ingredients [Member]
Disaggregation Of Revenue [Line Items]
Sales		839	837	794
Poly-vinyl pyrrolidones [Member] | Specialty Ingredients [Member]
Disaggregation Of Revenue [Line Items]
Sales		413	422	402
Adhesives [Member] | Specialty Ingredients [Member]
Disaggregation Of Revenue [Line Items]
Sales		345	351	336
Actives [Member] | Specialty Ingredients [Member]
Disaggregation Of Revenue [Line Items]
Sales		156	153	128
Vinyl Ethers [Member] | Specialty Ingredients [Member]
Disaggregation Of Revenue [Line Items]
Sales		106	139	139
Pharmachem [Member] | Specialty Ingredients [Member]
Disaggregation Of Revenue [Line Items]
Sales		231	248	104
Other [Member] | Specialty Ingredients [Member]
Disaggregation Of Revenue [Line Items]
Sales	[1]	292	320	313
Derivatives [Member] | Intermediates and Solvents [Member]
Disaggregation Of Revenue [Line Items]
Sales		92	99	77
Butanediol [Member] | Intermediates and Solvents [Member]
Disaggregation Of Revenue [Line Items]
Sales		$ 19	$ 20	$ 16

[1] Other includes no product category in excess of 10% of sales.