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Restructuring and Other Charges - Summary of Restructuring and Other Charges Impacts on Reportable Segment Income by Line of Business (Details) - USD ($) $ in Thousands	3 Months Ended	12 Months Ended
	Sep. 30, 2022	Sep. 30, 2022	Oct. 01, 2021	Oct. 02, 2020
Restructuring Cost and Reserve [Line Items]
Restructuring charges		$ 25,824
Recorded third-party environmental recoveries receivable	$ 27,000	27,000
Impairment of real estate		71,000	$ 2,400	$ 161,400
Gain (Loss) on Termination of Lease		(8,700)
Impairment of equity method investment				(162,000)
AWE ML
Restructuring Cost and Reserve [Line Items]
Gain (Loss) on Termination of Lease		(8,700)
Impairment of equity method investment			(38,500)
CH2M HILL Companies, Ltd.
Restructuring Cost and Reserve [Line Items]
Restructuring charges		161,063	99,590	324,183
Pre-tax settlement less insurance recoveries	91,300	91,300
Impairment of real estate	$ 78,300		2,400	161,400
Gain (Loss) on Termination of Lease		8,700
Impairment of equity method investment		(91,300)
CH2M HILL Companies, Ltd. \| Continuing Operations
Restructuring Cost and Reserve [Line Items]
Restructuring charges		161,063	99,590	324,183
CH2M HILL Companies, Ltd. \| Operating profit (mainly Selling, General and Administrative costs (“SG&A")
Restructuring Cost and Reserve [Line Items]
Restructuring charges		173,555	61,042	322,082
CH2M HILL Companies, Ltd. \| Other (Income) Expense, net
Restructuring Cost and Reserve [Line Items]
Restructuring charges		(12,492)	38,548	2,101
CH2M HILL Companies, Ltd. \| Operating Segments \| Critical Mission Solutions
Restructuring Cost and Reserve [Line Items]
Restructuring charges		5,626	5,079	24,083
CH2M HILL Companies, Ltd. \| Operating Segments \| People & Places Solutions
Restructuring Cost and Reserve [Line Items]
Restructuring charges		64,204	7,077	170,631
CH2M HILL Companies, Ltd. \| Operating Segments \| PA Consulting
Restructuring Cost and Reserve [Line Items]
Restructuring charges		4,253	15,566	0
CH2M HILL Companies, Ltd. \| Corporate
Restructuring Cost and Reserve [Line Items]
Restructuring charges		$ 86,980	$ 71,868	$ 129,469