Business Combinations (Pro-forma Results) (Details) (Sinclair Knight Merz [Member], USD $) In Millions, except Per Share data, unless otherwise specified	6 Months Ended
Mar. 28, 2014	Mar. 29, 2013
Pro Forma Results [Abstract]
Revenues	$ 6,495	$ 6,328
Net earnings attributable to Jacobs	183.0	220.0
Basic earnings per share (in dollars per share)	$ 1.40	$ 1.71
Diluted earnings per share (in dollars per share)	$ 1.38	$ 1.69
Acquisition-related Costs [Member]
Pro Forma Results [Abstract]
Net earnings attributable to Jacobs	$ 21.1	$ (22.7)

The pro forma basic net income per share for a period as if the business combination or combinations had been completed at the beginning of a period.

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 805

-SubTopic 10

-Section 50

-Paragraph 2

-Subparagraph (h)(2)-(3)

-URI http://asc.fasb.org/extlink&oid=25497992&loc=d3e1392-128463

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The pro forma diluted net income per share for a period as if the business combination or combinations had been completed at the beginning of a period.

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The pro forma net Income or Loss for the period as if the business combination or combinations had been completed at the beginning of a period.

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The pro forma revenue for a period as if the business combination or combinations had been completed at the beginning of the period.

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