Discontinued Operations- Schedule of Earnings (Loss) From Discontinued Operations, Net of tax (Details) - USD ($) $ in Thousands	12 Months Ended
	Sep. 26, 2025	Sep. 27, 2024	Sep. 29, 2023
Disposal Group, Including Discontinued Operation, Income Statement Disclosures [Abstract]
Net (Loss) Earnings of the Group from Discontinued Operations	$ (23,966)	$ 206,850	$ 300,017
Net Earnings Attributable to Noncontrolling Interests from Discontinued Operations	0	(13,561)	(13,365)
Net (Loss) Earnings Attributable to Jacobs from Discontinued Operations	(23,966)	193,289	286,652
Disposal group, including discontinued operation, liabilities	30,800
Professional services and other transaction related expenses		97,600
Discontinued Operations, Spinoff | SpinCo Business
Disposal Group, Including Discontinued Operation, Income Statement Disclosures [Abstract]
Revenues	(3,200)	5,472,979	5,500,994
Direct cost of contracts	3,528	(4,692,921)	(4,738,539)
Gross profit	328	780,058	762,455
Selling, general and administrative expense	(34,716)	(479,582)	(363,703)
Operating (Loss) Profit	(34,388)	300,476	398,752
Other loss, net	0	(3,301)	(3,049)
(Loss) Earnings Before Taxes from Discontinued Operations	(34,388)	297,175	395,703
Income Tax Benefit (Expense)	7,742	(89,737)	(94,845)
Net (Loss) Earnings of the Group from Discontinued Operations	(26,646)	207,438	300,858
Net Earnings Attributable to Noncontrolling Interests from Discontinued Operations	0	(13,561)	(13,365)
Net (Loss) Earnings Attributable to Jacobs from Discontinued Operations	$ (26,646)	$ 193,877	$ 287,493