Litigation, Claims and Contingencies - Schedule of Progression of Activity in the Asbestos Reserve (Details) - USD ($) $ in Millions	3 Months Ended	6 Months Ended			12 Months Ended
	Jun. 30, 2019	Mar. 31, 2020		Mar. 31, 2019	Sep. 30, 2019		Sep. 30, 2018	Sep. 30, 2017
Ashland [Member]
Asbestos reserve [Roll Forward]
Asbestos reserve - beginning of year	$ 366	$ 352	[1]	$ 380	$ 380		$ 419	$ 415
Reserve adjustment	1	0		0	1		(8)	36
Amounts paid		(15)		(14)	(29)		(31)	(32)
Asbestos reserve - end of period		337	[1]	366	352	[1]	380	419
Hercules [Member]
Asbestos reserve [Roll Forward]
Asbestos reserve - beginning of year	272	252	[2]	282	282		323	321
Reserve adjustment	$ (10)	0		0	(10)		(19)	16
Amounts paid		(10)		(10)	(20)		(22)	(14)
Asbestos reserve - end of period		$ 242	[2]	$ 272	$ 252	[2]	$ 282	$ 323

[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.