Litigation, Claims and Contingencies - Summary of Progression of Insurance Receivable (Parenthetical) (Details) - USD ($) $ in Millions		6 Months Ended
		Mar. 31, 2021		Mar. 31, 2022		Sep. 30, 2021		Sep. 30, 2020		Sep. 30, 2019		Sep. 30, 2018
Ashland [Member]
Movement in Loss Contingency Receivable, Increase (Decrease) [Roll Forward]
Insurance receivable		$ 96	[1]	$ 98	[1]	$ 100	[1]	$ 103	[1]	$ 123	[1]	$ 140
Allowance for credit losses		2
Total allowance for credit losses				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		46	[2]	46	[2]	47	[2]	$ 47	[2]	$ 49	[2]	$ 54
Allowance for credit losses		$ 1
Total allowance for credit losses				1
Hercules [Member] | Accounts Receivable [Member]
Movement in Loss Contingency Receivable, Increase (Decrease) [Roll Forward]
Insurance receivable				$ 1		$ 1

[1] Includes $12 million classified in accounts receivable on the Condensed Consolidated Balance Sheets as of March 31, 2022 and September 30, 2021.

[2] Includes $1 million classified in accounts receivable on the Condensed Consolidated Balance Sheets as of March 31, 2022 and September 30, 2021.