Long-term Debt (Revolving Credit Facility) (Details)	3 Months Ended
Jan. 01, 2016 USD ($) tranche
Line of Credit Facility [Line Items]
Total issued letters of credit	$ 240,900,000
Number of tranches in revolving credit facility (in tranches) \| tranche	2
Letter of Credit
Line of Credit Facility [Line Items]
Credit facility, maximum borrowing capacity	$ 300,000,000
Subfacility of Swingline Loans
Line of Credit Facility [Line Items]
Credit facility, maximum borrowing capacity	$ 50,000,000
Minimum
Line of Credit Facility [Line Items]
Facility fee percentage	0.10%
Minimum \| Eurocurrency Interest Rate
Line of Credit Facility [Line Items]
Margin added to variable rate interest rate (percentage)	1.00%
Minimum \| Base Interest Rate
Line of Credit Facility [Line Items]
Margin added to variable rate interest rate (percentage)	0.00%
Maximum
Line of Credit Facility [Line Items]
Facility fee percentage	0.25%
Maximum \| Eurocurrency Interest Rate
Line of Credit Facility [Line Items]
Margin added to variable rate interest rate (percentage)	1.50%
Maximum \| Base Interest Rate
Line of Credit Facility [Line Items]
Margin added to variable rate interest rate (percentage)	0.50%
2014 Facility
Line of Credit Facility [Line Items]
Available borrowing capacity	$ 975,600,000
2014 Facility \| Revolving Credit Facility
Line of Credit Facility [Line Items]
Credit facility, maximum borrowing capacity	1,600,000,000
Credit facility potential borrowing capacity	2,100,000,000
Direct borrowings on credit facility	621,900,000
2014 Facility \| Letter of Credit
Line of Credit Facility [Line Items]
Direct borrowings on credit facility	2,500,000
Committed and Uncommitted Letter of Credit Facility \| Letter of Credit
Line of Credit Facility [Line Items]
Direct borrowings on credit facility	$ 238,400,000

Line of Credit Facility, Accordion Feature, Potential Borrowing Capacity

No definition available.

Name:	jec_LineofCreditFacilityAccordionFeaturePotentialBorrowingCapacity
Namespace Prefix:	jec_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Number of Tranches in Revolving Credit Facility

+ References

No definition available.

+ Details

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Namespace Prefix:	jec_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	duration

- Definition

Percentage points added to the reference rate to compute the variable rate on the debt instrument.

+ References

No definition available.

+ Details

Name:	us-gaap_DebtInstrumentBasisSpreadOnVariableRate1
Namespace Prefix:	us-gaap_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

- Definition

The total amount of the contingent obligation under letters of credit outstanding as of the reporting date.

+ References

No definition available.

+ Details

Name:	us-gaap_LettersOfCreditOutstandingAmount
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

The carrying value as of the balance sheet date of the current and noncurrent portions of long-term obligations drawn from a line of credit, which is a bank's commitment to make loans up to a specific amount. Examples of items that might be included in the application of this element may consist of letters of credit, standby letters of credit, and revolving credit arrangements, under which borrowings can be made up to a maximum amount as of any point in time conditional on satisfaction of specified terms before, as of and after the date of drawdowns on the line. Includes short-term obligations that would normally be classified as current liabilities but for which (a) postbalance sheet date issuance of a long term obligation to refinance the short term obligation on a long term basis, or (b) the enterprise has entered into a financing agreement that clearly permits the enterprise to refinance the short-term obligation on a long term basis and the following conditions are met (1) the agreement does not expire within 1 year and is not cancelable by the lender except for violation of an objectively determinable provision, (2) no violation exists at the BS date, and (3) the lender has entered into the financing agreement is expected to be financially capable of honoring the agreement.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 942
-SubTopic 210
-Section S99
-Paragraph 1
-Subparagraph (SX 210.9-03.16)
-URI http://asc.fasb.org/extlink&oid=6876686&loc=d3e534808-122878

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 944
-SubTopic 210
-Section S99
-Paragraph 1
-Subparagraph (SX 210.7-03.16)
-URI http://asc.fasb.org/extlink&oid=6879938&loc=d3e572229-122910

Reference 3: http://www.xbrl.org/2003/role/presentationRef
-Publisher SEC
-Name Regulation S-X (SX)
-Number 210
-Section 02
-Paragraph 19, 20, 22
-Article 5

+ Details

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Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

The fee, expressed as a percentage of the line of credit facility, for the line of credit facility regardless of whether the facility has been used.

+ References

No definition available.

+ Details

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Namespace Prefix:	us-gaap_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

- Definition

Amount of current borrowing capacity under the credit facility considering any current restrictions on the amount that could be borrowed (for example, borrowings may be limited by the amount of current assets), but without considering any amounts currently outstanding under the facility.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02.19(b),22(b))
-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher SEC
-Name Regulation S-X (SX)
-Number 210
-Section 02
-Paragraph 19, 22
-Article 5

+ Details

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Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- 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

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Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Definition

Maximum borrowing capacity under the credit facility without consideration of any current restrictions on the amount that could be borrowed or the amounts currently outstanding under the facility.

+ References

+ Details

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Namespace Prefix:	us-gaap_
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Period Type:	instant

- Details

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- Details

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- Details

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