PA Consulting Business Combinations - Schedule of Unaudited Proforma Operating Results (Details) - PA Consulting Group Limited $ / shares in Units, $ in Millions	12 Months Ended
	Oct. 01, 2021 USD ($) $ / shares
Business Acquisition [Line Items]
Revenues	$ 14,504.3
Net earnings of the Group	695.1
Net earnings attributable to Jacobs	$ 548.0
Net earnings attributable to Jacobs per share:
Basic earnings (loss) per share (in dollars per share) | $ / shares	$ 4.21
Diluted earnings (loss) per share (in dollars per share) | $ / shares	$ 4.17
Business acquisitions pro forma income tax expense (benefit)	$ 330.7