Restructuring and Other Charges - Summary of Restructuring and Other Activities by Major Type of Costs (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Apr. 01, 2022	Apr. 02, 2021	Apr. 01, 2022	Apr. 02, 2021
Restructuring Cost and Reserve [Line Items]
Impairment of equity method investment			$ 74,585	$ 33,197
People & Places Solutions
Restructuring Cost and Reserve [Line Items]
Real estate impairment and other transformation activities			71,000
AWE Management Ltd
Restructuring Cost and Reserve [Line Items]
Impairment of equity method investment		$ 33,200		33,200
Other | AWE Management Ltd
Restructuring Cost and Reserve [Line Items]
Impairment of equity method investment				33,200
CH2M Hill, KeyM, John Wood Group Acquisitions and ECR Sale
Restructuring Cost and Reserve [Line Items]
Restructuring costs	$ 108,164	30,347	177,524	78,741
CH2M Hill, KeyM, John Wood Group Acquisitions and ECR Sale | Lease Abandonments and Impairments
Restructuring Cost and Reserve [Line Items]
Restructuring costs	2,294	2,062	67,837	2,211
CH2M Hill, KeyM, John Wood Group Acquisitions and ECR Sale | Voluntary and Involuntary Terminations
Restructuring Cost and Reserve [Line Items]
Restructuring costs	4,548	3,032	5,111	12,536
CH2M Hill, KeyM, John Wood Group Acquisitions and ECR Sale | Outside Services
Restructuring Cost and Reserve [Line Items]
Restructuring costs	11,500	18,314	16,176	25,713
CH2M Hill, KeyM, John Wood Group Acquisitions and ECR Sale | Other
Restructuring Cost and Reserve [Line Items]
Restructuring costs	89,822	$ 6,939	88,400	$ 38,281
CH2M HILL Companies, Ltd.
Restructuring Cost and Reserve [Line Items]
Loss related to settlement	$ 91,300		$ 91,300