Litigation, Claims and Contingencies - Summary of Components of Environmental Remediation Expense Included within Selling, General and Administrative Expense (Details) - USD ($) $ in Millions		3 Months Ended		9 Months Ended
		Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020
Loss Contingencies [Line Items]
Environmental expense		$ 24	$ 29	$ 39	$ 39
Accretion		0	0	1	1
Legal expense		1	1	2	4
Total expense		25	30	42	44
Insurance receivable		0	(1)	(1)	(4)
Total expense, net of receivable activity	[1]	$ 25	$ 29	$ 41	$ 40

[1] Net expense of $3 million and $6 million for the three and nine months ended June 30, 2021, respectively, and $8 million and $10 million for the three and nine months ended June 30, 2020, relates to divested businesses which qualified for treatment as discontinued operations for which certain environmental liabilities were retained by Ashland. These amounts are classified within the income from discontinued operations caption of the Statements of Consolidated Comprehensive Income (loss).