XML 81 R69.htm IDEA: XBRL DOCUMENT
v3.10.0.1

Derivatives - Details of Derivatives Held to Manage Foreign Currency Risk (Detail) | Jun. 30, 2018 USD ($) | Jun. 30, 2018 EUR (€) | Sep. 30, 2017 USD ($) | Sep. 30, 2017 EUR (€)
--- | --- | --- | --- | ---
Net Investment [Member] | Cross Currency Swaps [Member] |  |  |  |  |
Derivative [Line Items] |  |  |  |  |
Notional Amount |  | $ 250,000,000 |  |  |
Net Investment [Member] | 3.4% Notes [Member] | Cross Currency Swaps [Member] |  |  |  |  |
Derivative [Line Items] |  |  |  |  |
Notional Amount |  | $ 250,000,000 | € 223,000,000 | $ 250,000,000 | € 223,000,000
Net Investment [Member] | 3.4% Notes [Member] | Fixed Rate Debt [Member] | Cross Currency Swaps [Member] |  |  |  |  |
Derivative [Line Items] |  |  |  |  |
Interest rate on borrowing |  | 3.40% | 3.40% | 3.40% | 3.40%
Not Designated as Hedging Instrument [Member] | Forward Foreign Currency Contracts [Member] |  |  |  |  |
Derivative [Line Items] |  |  |  |  |
Notional Amount | [1] | $ (6,000,000) |  | $ 5,000,000 |
[1] | Cabot’s forward foreign exchange contracts are denominated in the Indonesian rupiah and Czech koruna.

X
- Definition Derivative notional amount lower buying higher selling of foreign exchange. + References No definition available. + Details
Name: | cbt_DerivativeNotionalAmountLowerBuyingHigherSellingOfForeignExchange
Namespace Prefix: | cbt_
Data Type: | xbrli:monetaryItemType
Balance Type: | na
Period Type: | instant

X
- Definition Aggregate notional amount specified by the derivative(s). Expressed as an absolute value. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Regulation S-X (SX) -Number 210 -Article 12 -Section 13 -Sentence Column B + Details
Name: | invest_DerivativeNotionalAmount
Namespace Prefix: | invest_
Data Type: | xbrli:monetaryItemType
Balance Type: | na
Period Type: | instant

X
- Definition Contractual interest rate for funds borrowed, under the debt agreement. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 210 -SubTopic 10 -Section S99 -Paragraph 1 -Subparagraph (SX 210.5-02.22(a)(1)) -URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682 + Details
Name: | us-gaap_DebtInstrumentInterestRateStatedPercentage
Namespace Prefix: | us-gaap_
Data Type: | num:percentItemType
Balance Type: | na
Period Type: | instant

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_DerivativeLineItems
Namespace Prefix: | us-gaap_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration

X
- Details
Name: | us-gaap_DerivativeInstrumentsGainLossByHedgingRelationshipAxis=us-gaap_NetInvestmentHedgingMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_DerivativeInstrumentRiskAxis=us-gaap_CrossCurrencyInterestRateContractMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

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

X
- Details
Name: | us-gaap_LongtermDebtTypeAxis=cbt_FixedRateDebtMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_HedgingDesignationAxis=us-gaap_NondesignatedMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_FinancialInstrumentAxis=us-gaap_ForwardContractsMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |