Commitments and Contingencies and Derivative Financial Instruments	3 Months Ended
	Dec. 30, 2022
Commitments and Contingencies Disclosure [Abstract]
Commitments and Contingencies and Derivative Financial Instruments	Commitments and Contingencies and Derivative Financial Instruments Derivative Financial Instruments The Company is exposed to interest rate risk under its variable rate borrowings and additionally, due to the nature of the Company's international operations, we are at times exposed to foreign currency risk. As such, we sometimes enter into foreign exchange hedging contracts and interest rate hedging contracts in order to limit our exposure to fluctuating foreign currencies and interest rates. During fiscal 2022, the Company entered into two treasury lock agreements with a total notional value of $500.0 million to manage its interest rate exposure to the anticipated issuance of fixed rate debt before December 2023. The fair value of the treasury locks at December 30, 2022 and September 30, 2022 was $41.5 million and $40.9 million, respectively, all of which is included in current assets within receivables and contract assets on the consolidated balance sheets. The unrealized net gain on these instruments was $31.3 million and $30.8 million, net of tax, and is included in accumulated other comprehensive income as of December 30, 2022 and September 30, 2022, respectively. Upon issuance of up to $500 million of fixed rate debt, the gain (loss) will be amortized to interest expense over the term of the debt. The Company is party to interest rate swap agreements and a cross-currency swap agreement with notional values of $766.7 million and $127.8 million, respectively, as of December 30, 2022 to manage the interest rate exposure on our variable rate loans and the foreign currency exposure on our USD borrowings by a European subsidiary. By entering into the swap agreements, the Company converted the LIBOR and SONIA rate based liabilities into fixed rate liabilities and, for the cross currency swap, our LIBOR rate based borrowing in USD to a fixed rate Euro liability, for periods ranging from three and a half to ten years. The swaps were designated as cash-flow hedges in accordance with ASC 815, Derivatives and Hedging. The fair value of the interest rate and cross currency swaps at December 30, 2022 and September 30, 2022 was $108.0 million and $128.2 million, respectively, which is included in miscellaneous other assets on the Consolidated Balance Sheets. The unrealized net gain (loss) on these interest rate and cross currency swaps was $80.2 million and $87.5 million, net of tax, and was included in accumulated other comprehensive income as of December 30, 2022 and September 30, 2022, respectively. Additionally, the Company held foreign exchange forward contracts in currencies that support our operations, including British Pound, Euro, Australian Dollar and other currencies, with notional values of $382.5 million at December 30, 2022 and $298.2 million at September 30, 2022. The length of these contracts currently ranges from one to 12 months. The fair value of the foreign exchange contracts at December 30, 2022 and September 30, 2022 was $12.1 million and $(3.2) million, respectively, which is included within receivables and contract assets for the current period and within accounts payable for the prior period on the Consolidated Balance Sheets and with associated income statement impacts included in miscellaneous income (expense) in the Consolidated Statements of Earnings. The fair value measurements of these derivatives are being made using Level 2 inputs under ASC 820, Fair Value Measurement, as the measurements are based on observable inputs other than quoted prices in active markets. We are exposed to risk from credit-related losses resulting from nonperformance by counterparties to our financial instruments. We perform credit evaluations of our counterparties under forward exchange and interest rate contracts and expect all counterparties to meet their obligations. We have not experienced credit losses from our counterparties. Contractual Guarantees and Insurance In the normal course of business, we make contractual commitments (some of which are supported by separate guarantees) and on occasion we are a party in a litigation or arbitration proceeding. The litigation or arbitration in which we are involved includes personal injury claims, professional liability claims and breach of contract claims. Where we provide a separate guarantee, it is strictly in support of the underlying contractual commitment. Guarantees take various forms including surety bonds required by law, or standby letters of credit ("LOC" and also referred to as “bank guarantees”) or corporate guarantees given to induce a party to enter into a contract with a subsidiary. Standby LOCs are also used as security for advance payments or in various other transactions. The guarantees have various expiration dates ranging from an arbitrary date to completion of our work (e.g., engineering only) to completion of the overall project. We record in the Consolidated Balance Sheets amounts representing our estimated liability relating to such guarantees, litigation and insurance claims. Guarantees are accounted for in accordance with ASC 460-10, Guarantees, at fair value at the inception of the guarantee. At December 30, 2022 and September 30, 2022, the Company had issued and outstanding approximately $292.5 million and $280.5 million, respectively, in LOCs and $2.0 billion and $2.2 billion, respectively, in surety bonds. We maintain insurance coverage for most insurable aspects of our business and operations. Our insurance programs have varying coverage limits depending upon the type of insurance and include certain conditions and exclusions which insurance companies may raise in response to any claim that is asserted by or against the Company. We have also elected to retain a portion of losses and liabilities that occur through using various deductibles, limits, and retentions under our insurance programs. As a result, we may be subject to a future liability for which we are only partially insured or completely uninsured. We intend to mitigate any such future liability by continuing to exercise prudent business judgment in negotiating the terms and conditions of the contracts which the Company enters with its clients. Our insurers are also subject to business risk and, as a result, one or more of them may be unable to fulfill their insurance obligations due to insolvency or otherwise. Additionally, as a contractor providing services to the U.S. federal government, we are subject to many types of audits, investigations, and claims by, or on behalf of, the government including with respect to contract performance, pricing, cost allocations, procurement practices, labor practices, and socioeconomic obligations. Furthermore, our income, franchise, and similar tax returns and filings are also subject to audit and investigation by the Internal Revenue Service, most states within the United States, as well as by various government agencies representing jurisdictions outside the United States. Our Consolidated Balance Sheets include amounts representing our probable estimated liability relating to such claims, guarantees, litigation, audits, and investigations. We perform an analysis to determine the level of reserves to establish for insurance-related claims that are known and have been asserted against us, as well as for insurance-related claims that are believed to have been incurred based on actuarial analysis but have not yet been reported to our claims administrators as of the respective balance sheet dates. We include any adjustments to such insurance reserves in our consolidated results of operations. Insurance recoveries are recorded as assets if recovery is probable and estimated liabilities are not reduced by expected insurance recoveries. The Company believes, after consultation with counsel, that such guarantees, litigation, U.S. government contract-related audits, investigations and claims, and income tax audits and investigations should not have a material adverse effect on our consolidated financial statements, beyond amounts currently accrued. Litigation and Investigations On December 22, 2008, a coal fly ash pond at the Kingston Power Plant of the Tennessee Valley Authority ("TVA") was breached, releasing fly ash waste into the Emory River and surrounding community. In February 2009, TVA awarded a contract to the Company to provide project management services associated with the clean-up. All remediation and dredging were completed in August 2013 by other contractors under direct contracts with TVA. The Company did not perform the remediation, and its scope was limited to program management services. Certain employees of the contractors performing the cleanup work on the project filed lawsuits against the Company beginning in August 2013, alleging they were injured due to the Company's failure to protect the plaintiffs from exposure to fly ash, and asserting related personal injuries. The primary case, Greg Adkisson, et al. v. Jacobs Engineering Group Inc., case No. 3:13-CV-505-TAV-HBG, filed in the U.S. District Court for the Eastern District of Tennessee, consists of 10 consolidated cases. This case and the related cases involve several hundred plaintiffs that were employees of the contractors that completed the remediation and dredging work. The cases are at various stages of litigation and are currently stayed pending a ruling from the Tennessee Supreme Court. Additionally, in May 2019, Roane County and the cities of Kingston and Harriman filed a lawsuit against TVA and the Company alleging that they misled the public about risks associated with the released fly ash. In October 2020, the Court granted Jacobs and TVA’s motion to dismiss the Roane County litigation and closed the case. In addition, in November 2019, a resident of Roane County, Margie Delozier, filed a putative class action against TVA and the Company alleging they failed to adequately warn local residents about risks associated with the released fly ash. The Company and TVA filed separate motions to dismiss the Delozier case in April 2020. In February 2021, the Court granted dismissal of the Delozier Complaint with prejudice, with the exception of plaintiffs’ nuisance cause of action, which plaintiffs voluntarily dismissed in June 2021. In August 2021, Thomas Ryan, a resident of Roane County, filed an action against Jacobs and TVA claiming personal injury and property damage. In June 2022, the Court granted Jacobs' motion to dismiss Ryan’s action in its entirety, closing the case. Separately, in February 2020, the Company learned that the district attorney in Roane County recommended that the Tennessee Bureau of Investigation investigate issues pertaining to clean up worker safety at Kingston. On November 16, 2021, the Roane County district attorney announced that it had concluded its investigation into issues pertaining to the Kingston coal ash spill cleanup. No indictments were issued. There has been no finding of liability against the Company or that any of the alleged illnesses are the result of exposure to fly ash in any of the above matters. The Company disputes the allegations asserted in all of the above matters and is vigorously defending these matters. The Company does not expect the resolution of these matters to have a material adverse effect on the Company's business, financial condition, results of operations or cash flows.