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Savings and Deferred Compensation Plans Savings and Deferred Compensation Plans (Savings Plans) (Details) - USD ($) $ in Thousands | 12 Months Ended
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Oct. 02, 2020 | Sep. 27, 2019 | Sep. 28, 2018
Savings And Deferred Compensation Plans [Abstract] |  |  |
Savings plans contributions | $ 91,833 | $ 114,006 | $ 113,135

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- Definition Defined Contribution Plan Savings Plans Contributions + References No definition available. + Details
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- Definition Savings And Deferred Compensation Plans [Abstract] + References No definition available. + Details
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Namespace Prefix: | jec_
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Balance Type: | na
Period Type: | duration