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Divestitures - Additional Information (Details) - USD ($) $ in Millions	3 Months Ended			9 Months Ended
	Jun. 30, 2025	Mar. 31, 2025	Jun. 30, 2024	Jun. 30, 2025	Jun. 30, 2024
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Net proceeds from sale of business		$ 16		$ 16	$ 0
Income (loss) on acquisitions and divestitures	$ (0)		$ (99)	(165)	(100)
Land and Building [Member] \| Composites Segment and the Intermediates and Solvents Marl Facility [Member]
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Net proceeds from sale of business				11
Income (loss) on acquisitions and divestitures				11
Sale of properties with net book value		$ 0
Discontinued Operations, Held-for-sale [Member]
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Income (loss) on acquisitions and divestitures				8
Impairment charge			$ 99	183	$ 99
Discontinued Operations, Held-for-sale [Member] \| Goodwill [Member]
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Impairment charge				1
Discontinued Operations, Held-for-sale [Member] \| Other Intangible Assets [Member]
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Impairment charge				134
Discontinued Operations, Held-for-sale [Member] \| Property, Plant and Equipment [Member]
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Impairment charge				33
Discontinued Operations, Held-for-sale [Member] \| Operating Lease Assets Net [Member]
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Impairment charge				14
Discontinued Operations, Held-for-sale [Member] \| Other Current Assets [Member]
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Impairment charge				$ 1