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Financial Information by Segment - Additional Information (Detail) | 6 Months Ended
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Mar. 31, 2016 Segment Business_Unit
Segment Reporting Information [Line Items] |
Number of business reportable segments | Segment | 4
Performance Chemicals [Member] |
Segment Reporting Information [Line Items] |
Number of business activity | Business_Unit | 2

X
- Definition Number of business activity. + References No definition available. + Details
Name: | cbt_NumberOfBusinessActivity
Namespace Prefix: | cbt_
Data Type: | xbrli:integerItemType
Balance Type: | na
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. + References No definition available. + Details
Name: | us-gaap_NumberOfReportableSegments
Namespace Prefix: | us-gaap_
Data Type: | xbrli:integerItemType
Balance Type: | na
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_SegmentReportingInformationLineItems
Namespace Prefix: | us-gaap_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration

X
- Details
Name: | us-gaap_StatementBusinessSegmentsAxis=cbt_PerformanceChemicalsMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |