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, 2019	Mar. 31, 2018	Mar. 31, 2019	Mar. 31, 2018
Environmental Expense And Liabilities [Abstract]
Environmental expense		$ 3	$ 4	$ 6	$ 16
Accretion		1	0	1	1
Legal expense		2	2	3	3
Total expense		6	6	10	20
Insurance receivable	[1]	0	(1)	(1)	(1)
Total expense, net of receivable activity	[2]	$ 6	$ 5	$ 9	$ 19

[1] Activity of $0 denotes value less than $1 million.

[2] Net expense of $1 million and $2 million for the three and six months ended March 31, 2019, and $1 million for both the three and six months ended March 31, 2018, 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).