Revenue - Disaggregation of Revenue (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Jun. 30, 2025	Jun. 30, 2024	Jun. 30, 2025	Jun. 30, 2024
Disaggregation Of Revenue [Line Items]
Sales	$ 463	$ 544	$ 1,347	$ 1,591
Life Sciences [Member]
Disaggregation Of Revenue [Line Items]
Sales	162	195	468	617
Life Sciences [Member] \| North America [Member]
Disaggregation Of Revenue [Line Items]
Sales	31	56	84	197
Life Sciences [Member] \| Europe [Member]
Disaggregation Of Revenue [Line Items]
Sales	60	65	179	200
Life Sciences [Member] \| Asia Pacific [Member]
Disaggregation Of Revenue [Line Items]
Sales	52	58	151	165
Life Sciences [Member] \| Latin America & Other [Member]
Disaggregation Of Revenue [Line Items]
Sales	19	16	54	55
Personal Care [Member]
Disaggregation Of Revenue [Line Items]
Sales	147	175	426	473
Personal Care [Member] \| North America [Member]
Disaggregation Of Revenue [Line Items]
Sales	35	51	116	136
Personal Care [Member] \| Europe [Member]
Disaggregation Of Revenue [Line Items]
Sales	59	65	163	181
Personal Care [Member] \| Asia Pacific [Member]
Disaggregation Of Revenue [Line Items]
Sales	34	37	94	94
Personal Care [Member] \| Latin America & Other [Member]
Disaggregation Of Revenue [Line Items]
Sales	19	22	53	62
Specialty Additives [Member]
Disaggregation Of Revenue [Line Items]
Sales	131	150	380	429
Specialty Additives [Member] \| North America [Member]
Disaggregation Of Revenue [Line Items]
Sales	47	49	133	137
Specialty Additives [Member] \| Europe [Member]
Disaggregation Of Revenue [Line Items]
Sales	48	55	130	158
Specialty Additives [Member] \| Asia Pacific [Member]
Disaggregation Of Revenue [Line Items]
Sales	30	38	97	112
Specialty Additives [Member] \| Latin America & Other [Member]
Disaggregation Of Revenue [Line Items]
Sales	6	8	20	22
Intermediates [Member]
Disaggregation Of Revenue [Line Items]
Sales	33	36	104	108
Intermediates [Member] \| North America [Member]
Disaggregation Of Revenue [Line Items]
Sales	21	24	69	76
Intermediates [Member] \| Europe [Member]
Disaggregation Of Revenue [Line Items]
Sales	9	7	20	17
Intermediates [Member] \| Asia Pacific [Member]
Disaggregation Of Revenue [Line Items]
Sales	2	4	10	12
Intermediates [Member] \| Latin America & Other [Member]
Disaggregation Of Revenue [Line Items]
Sales	$ 1	$ 1	$ 5	$ 3