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Restructuring and Other Charges - Summary of Restructuring and Other Activities by Major Type of Costs (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Jul. 01, 2022	Jul. 02, 2021	Jul. 01, 2022	Jul. 02, 2021
Restructuring Cost and Reserve [Line Items]
Impairment of equity method investment			$ 74,585	$ 40,138
People & Places Solutions
Restructuring Cost and Reserve [Line Items]
Real estate impairment and other transformation activities			71,200
AWE Management Ltd
Restructuring Cost and Reserve [Line Items]
Impairment of equity method investment		$ 38,900		38,900
Other \| AWE Management Ltd
Restructuring Cost and Reserve [Line Items]
Impairment of equity method investment				38,900
CH2M Hill, KeyM, John Wood Group Acquisitions and ECR Sale
Restructuring Cost and Reserve [Line Items]
Restructuring costs	$ 4,577	13,768	182,100	92,509
CH2M Hill, KeyM, John Wood Group Acquisitions and ECR Sale \| Lease Abandonments and Impairments
Restructuring Cost and Reserve [Line Items]
Restructuring costs	(32)	354	67,805	2,565
Real estate impairment and other transformation activities			74,900
CH2M Hill, KeyM, John Wood Group Acquisitions and ECR Sale \| Voluntary and Involuntary Terminations
Restructuring Cost and Reserve [Line Items]
Restructuring costs	(76)	1,692	5,035	14,227
CH2M Hill, KeyM, John Wood Group Acquisitions and ECR Sale \| Outside Services
Restructuring Cost and Reserve [Line Items]
Restructuring costs	4,337	5,463	20,513	31,516
CH2M Hill, KeyM, John Wood Group Acquisitions and ECR Sale \| Other
Restructuring Cost and Reserve [Line Items]
Restructuring costs	$ 348	$ 6,259	88,747	$ 44,201
CH2M HILL Companies, Ltd.
Restructuring Cost and Reserve [Line Items]
Real estate impairment and other transformation activities			77,000
Loss related to settlement			$ 91,300