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Other Financial Information Other Financial Information (Narrative) (Details) | 12 Months Ended
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Sep. 28, 2018
Other Financial Information [Abstract] |
Billed receivables collection period (in months) | 12 months
Duration which unbilled amounts will be billed and collected over (duration) | 12 months

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- Definition Billed Receivables Collection Period + References No definition available. + Details
Name: | jec_BilledReceivablesCollectionPeriod
Namespace Prefix: | jec_
Data Type: | xbrli:durationItemType
Balance Type: | na
Period Type: | duration

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- Definition Other Financial Information [Abstract] + References No definition available. + Details
Name: | jec_OtherFinancialInformationAbstract
Namespace Prefix: | jec_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration

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- Definition Unbilled Amounts Billed And Collected + References No definition available. + Details
Name: | jec_UnbilledAmountsBilledAndCollected
Namespace Prefix: | jec_
Data Type: | xbrli:durationItemType
Balance Type: | na
Period Type: | duration