Debt instrument maturity year.

No definition available.

Name:	ash_DebtInstrumentMaturityYear
Namespace Prefix:	ash_
Data Type:	xbrli:gYearItemType
Balance Type:	na
Period Type:	duration

- Definition

The remaining balance of debt issuance expenses that were capitalized and are being amortized against income over the lives of the respective long-term debt and presented as a direct reduction to long-term debt.

+ References

No definition available.

+ Details

Name:	ash_UnamortizedDebtIssuanceExpenseLongTermDebt
Namespace Prefix:	ash_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Face (par) amount of debt instrument at time of issuance.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 835
-SubTopic 30
-Section 45
-Paragraph 2
-URI http://asc.fasb.org/extlink&oid=114775744&loc=d3e28551-108399

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 835
-SubTopic 30
-Section 55
-Paragraph 8
-URI http://asc.fasb.org/extlink&oid=114775985&loc=d3e28878-108400

+ Details

Name:	us-gaap_DebtInstrumentFaceAmount
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Contractual interest rate for funds borrowed, under the debt agreement.

+ References

+ Details

Name:	us-gaap_DebtInstrumentInterestRateStatedPercentage
Namespace Prefix:	us-gaap_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

- Definition

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

+ References

No definition available.

+ Details

Name:	us-gaap_DebtInstrumentLineItems
Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Definition

Reflects the total carrying amount as of the balance sheet date of debt having initial terms less than one year or the normal operating cycle, if longer.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02(19)(a))
-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 944
-SubTopic 210
-Section S99
-Paragraph 1
-Subparagraph (SX 210.7-03(a)(16)(a)(1))
-URI http://asc.fasb.org/extlink&oid=119400593&loc=d3e572229-122910

Reference 3: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 942
-SubTopic 210
-Section S99
-Paragraph 1
-Subparagraph (SX 210.9-03(13))
-URI http://asc.fasb.org/extlink&oid=6876686&loc=d3e534808-122878

+ Details

Name:	us-gaap_ShortTermBorrowings
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Details

Name:	us-gaap_DebtInstrumentAxis=ash_FourPointSevenFiveZeroPercentageNotesDue2022Member
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_DebtInstrumentAxis=ash_TwoPointZeroZeroPercentageSeniorNotesDue2028Member
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_DebtInstrumentAxis=ash_SixPointEightSevenFivePercentageNotesDue2043Member
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_DebtInstrumentAxis=ash_TermLoanADue2025Member
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_DebtInstrumentAxis=ash_SixPointFiveZeroPercentageJuniorSubordinatedNotesDue2029Member
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_DebtInstrumentAxis=ash_EuropeanFacilityMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

Debt - Summary of Current and Long-term Debt (Parenthetical) (Details) $ in Millions	6 Months Ended
	Mar. 31, 2020 USD ($)	Mar. 31, 2020 EUR (€)	Jan. 31, 2020 EUR (€)	Sep. 30, 2019 USD ($)
Debt Instrument [Line Items]
Unamortized debt issuance expense, long-term debt	$ 15			$ 12
Short-term debt outstanding balance	$ 471			166
4.750% Notes due 2022 [Member]
Debt Instrument [Line Items]
Debt instrument, interest rate, stated percentage	4.75%	4.75%
Debt instrument, maturity year	2022
2.00% Senior Notes Due 2028 [Member]
Debt Instrument [Line Items]
Debt instrument, interest rate, stated percentage	2.00%	2.00%	2.00%
Debt instrument, maturity year	2028
Principal amount \| €		€ 500,000,000	€ 500,000,000
6.875% Notes due 2043 [Member]
Debt Instrument [Line Items]
Debt instrument, interest rate, stated percentage	6.875%	6.875%
Debt instrument, maturity year	2043
Term Loan A due 2025 [Member]
Debt Instrument [Line Items]
Debt instrument, maturity year	2025
6.50% Junior Subordinated Notes, Due 2029 [Member]
Debt Instrument [Line Items]
Debt instrument, interest rate, stated percentage	6.50%	6.50%
Debt instrument, maturity year	2029
European Facility [Member]
Debt Instrument [Line Items]
Short-term debt outstanding balance	$ 22			$ 22