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Debt - Summary of Debt Issuance Cost Amortization (Parenthetical) (Details) $ in Millions | 12 Months Ended
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Sep. 30, 2017 USD ($)
Junior Subordinated Debt [Member] |
Debt Instrument [Line Items] |
Repayment of debt, accelerated accretion | $ 92

X
- Definition Accelerated accretion of the recorded debt discount due to termination or repayment of debt. + References No definition available. + Details
Name: | ash_RepaymentOfDebtAcceleratedAccretion
Namespace Prefix: | ash_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration

X
- 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

X
- Details
Name: | us-gaap_DebtInstrumentAxis=us-gaap_JuniorSubordinatedDebtMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |