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v3.25.3

Income Taxes - Expiration Dates of NOLs, Capital Loss and Other Tax Credit Carryforwards Before Valuation Allowances (Parenthetical) (Detail) | 12 Months Ended
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Sep. 30, 2025
Significant Tax Attributes And Dates Of Expiration [Line Items] |
Expiration periods | 2033
Minimum [Member] |
Significant Tax Attributes And Dates Of Expiration [Line Items] |
Expiration periods | 2026
Maximum [Member] |
Significant Tax Attributes And Dates Of Expiration [Line Items] |
Expiration periods | 2032

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- Definition Significant tax attributes and dates of expiration. + References No definition available. + Details
Name: | cbt_SignificantTaxAttributesAndDatesOfExpirationLineItems
Namespace Prefix: | cbt_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration

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- Definition Tax credit carryforward expiration period. + References No definition available. + Details
Name: | cbt_TaxCreditCarryforwardExpirationPeriod
Namespace Prefix: | cbt_
Data Type: | xbrli:gYearItemType
Balance Type: | na
Period Type: | duration

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- Details
Name: | srt_RangeAxis=srt_MinimumMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | srt_RangeAxis=srt_MaximumMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |