Income Taxes - Summary of Changes in Unrecognized Tax Benefits (Parenthetical) (Details) - USD ($) $ in Millions	Sep. 30, 2019	Sep. 30, 2018
Tax and tax indemnity receivables	$ 68	$ 74
Valvoline [Member]
Tax and tax indemnity receivables	$ 32	$ 39

Tax indemnity receivable established as a result of an acquisition of divestiture.

No definition available.

Name:	ash_TaxIndemnityReceivable
Namespace Prefix:	ash_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant