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Significant Accounting Policies - Additional Information (Details) shares in Millions, $ in Millions	7 Months Ended	9 Months Ended
	May 12, 2017 shares	Jun. 30, 2018 USD ($) ReportableSegment
Organization Consolidation And Presentation Of Financial Statements [Abstract]
Valvoline Shares Owned by Ashland | shares	170
Sale of Stock, Percentage of Ownership after Transaction	83.00%
Number of reportable segments | ReportableSegment		3
Expenses reclassified to other net periodic benefit income | $		$ 3

X

- Definition

Expenses reclassfied to other defined benefit plan net periodic benefit income.

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No definition available.

+ Details

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Namespace Prefix:	ash_
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X

- Definition

The number of Valvoline Inc. shares owned by Ashland after the initial public offering of Valvoline Inc. was completed.

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No definition available.

+ Details

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Namespace Prefix:	ash_
Data Type:	xbrli:sharesItemType
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Period Type:	duration

X

- Definition

Number of segments reported by the entity. A reportable segment is a component of an entity for which there is an accounting requirement to report separate financial information on that component in the entity's financial statements.

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No definition available.

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Balance Type:	na
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- Definition

Percentage of subsidiary's or equity investee's stock owned by parent company after stock transaction.

+ References

No definition available.

+ Details

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Namespace Prefix:	us-gaap_
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