Litigation, Claims and Contingencies - Summary of Progression of Insurance Receivable (Parenthetical) (Details) - USD ($) $ in Millions		12 Months Ended
		Sep. 30, 2021		Mar. 31, 2023		Sep. 30, 2022		Mar. 31, 2022		Sep. 30, 2020		Sep. 30, 2019
Ashland [Member]
Movement in Loss Contingency Receivable, Increase (Decrease) [Roll Forward]
Insurance receivable		$ 100	[1]	$ 96	[1]	$ 101	[1]	$ 98	[1]	$ 103	[1]	$ 123
Allowance for credit losses		2
Total allowance for credit losses				2		2
Ashland [Member] | Accounts Receivable [Member]
Movement in Loss Contingency Receivable, Increase (Decrease) [Roll Forward]
Insurance receivable	[1]			12		12
Hercules [Member]
Movement in Loss Contingency Receivable, Increase (Decrease) [Roll Forward]
Insurance receivable		47	[2]	51	[2]	52	[2]	$ 46	[2]	$ 47	[2]	$ 49
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				$ 2		$ 3

[1] Includes $12 million classified in accounts receivable on the Condensed Consolidated Balance Sheets as of March 31, 2023 and September 30, 2022.

[2] Includes $2 million and $3 million classified in accounts receivable on the Condensed Consolidated Balance Sheets as of March 31, 2023 and September 30, 2022, respectively.