Litigation, Claims and Contingencies - Summary of Progression of Insurance Receivable (Parenthetical) (Details) - USD ($) $ in Millions		12 Months Ended
		Sep. 30, 2021		Sep. 30, 2023		Sep. 30, 2022		Sep. 30, 2020
Movement in Loss Contingency Receivable, Increase (Decrease) [Roll Forward]
Insurance receivable	[1]	$ 47
Ashland [Member]
Movement in Loss Contingency Receivable, Increase (Decrease) [Roll Forward]
Insurance receivable		100	[2]	$ 95	[2]	$ 101	[2]	$ 103
Allowance for credit losses		2
Total allowance for credit losses				1		2
Ashland [Member] | Accounts Receivable [Member]
Movement in Loss Contingency Receivable, Increase (Decrease) [Roll Forward]
Insurance receivable				11		12
Hercules [Member]
Movement in Loss Contingency Receivable, Increase (Decrease) [Roll Forward]
Insurance receivable		47		47	[1]	52	[1]	$ 47
Allowance for credit losses		$ 1
Total allowance for credit losses				1		1
Hercules [Member] | Accounts Receivable [Member]
Movement in Loss Contingency Receivable, Increase (Decrease) [Roll Forward]
Insurance receivable				$ 4		$ 3

[1] Included $4 million and $3 million classified in accounts receivable on the Consolidated Balance Sheets as of September 30, 2023 and 2022, respectively.

[2] Included $11 million and $12 million classified in accounts receivable on the Consolidated Balance Sheets as of September 30, 2023 and 2022, respectively.