Litigation, Claims and Contingencies - Summary of Asbestos Claims Activity (Details) - Claim Claim in Thousands	6 Months Ended		12 Months Ended
	Mar. 31, 2020	Mar. 31, 2019	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2017
Ashland [Member]
Asbestos claims [Roll Forward]
Open claims - beginning of year	53	53	53	54	57
New claims filed	1	1	2	2	2
Claims settled	0	0	(1)	(1)	(1)
Claims dismissed	(4)	(1)	(1)	(2)	(4)
Open claims - end of period	50	53	53	53	54
Hercules [Member]
Asbestos claims [Roll Forward]
Open claims - beginning of year	13	13	13	12	15
New claims filed			1	2	1
Claims dismissed		(1)	(1)	(1)	(4)
Open claims - end of period	13	12	13	13	12