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		6 Months Ended
		Mar. 31, 2020	Mar. 31, 2019	Mar. 31, 2020	Mar. 31, 2019
Environmental Expense And Liabilities [Abstract]
Environmental expense		$ 8	$ 3	$ 10	$ 6
Accretion		1	1	1	1
Legal expense		1	2	3	3
Total expense		10	6	14	10
Insurance receivable		(3)	0	(3)	(1)
Total expense, net of receivable activity	[1]	$ 7	$ 6	$ 11	$ 9

[1] Net expense of $2 million for the three and six months ended March 31, 2020, and $1 million and $2 million the three and six months ended March 31, 2019, respectively, 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).