Litigation, Claims and Contingencies - Schedule of Progression of Activity in the Asbestos Reserve (Parenthetical) (Details) - USD ($) $ in Millions	Mar. 31, 2020		Sep. 30, 2019		Mar. 31, 2019	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2016
Ashland [Member]
Asbestos claims [Roll Forward]
Asbestos reserve	$ 337	[1]	$ 352	[1]	$ 366	$ 380	$ 419	$ 415
Ashland [Member] | Other Current Liabilities [Member]
Asbestos claims [Roll Forward]
Asbestos reserve	28		28
Hercules [Member]
Asbestos claims [Roll Forward]
Asbestos reserve	242	[2]	252	[2]	$ 272	$ 282	$ 323	$ 321
Hercules [Member] | Other Current Liabilities [Member]
Asbestos claims [Roll Forward]
Asbestos reserve	$ 21		$ 21

[1] Included $28 million classified in accrued expenses and other liabilities on the Condensed Consolidated Balance Sheets as of both March 31, 2020 and September 30, 2019.

[2] Included $21 million classified in accrued expenses and other liabilities on the Condensed Consolidated Balance Sheets as of both March 31, 2020 and September 30, 2019.