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Financial Information by Segment - Schedule of Income (Loss) from Continuing Operations before Income Taxes and Equity in Earnings of Affiliated Companies for Unallocated and Other (Parenthetical) (Detail) - USD ($) $ in Millions | 3 Months Ended | 9 Months Ended
--- | --- | ---
Jun. 30, 2017 | Jun. 30, 2017
Segment Reporting [Abstract] |  |
Increase (decrease) in general unallocated income expense | $ 2 | $ (4)

X
- Definition Decrease in general unallocated income (expense). + References No definition available. + Details
Name: | cbt_DecreaseInGeneralUnallocatedIncomeExpense
Namespace Prefix: | cbt_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration

X
- References No definition available. + Details
Name: | us-gaap_SegmentReportingAbstract
Namespace Prefix: | us-gaap_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration