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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	12 Months Ended
	Oct. 01, 2021	Oct. 02, 2020	Sep. 27, 2019
Restructuring Cost and Reserve [Line Items]
Restructuring charges	$ 99,590
Gain (loss) on litigation settlement	19,500
AWE ML
Restructuring Cost and Reserve [Line Items]
Impairment of equity method investment	(38,500)
CH2M HILL Companies, Ltd.
Restructuring Cost and Reserve [Line Items]
Restructuring charges	99,590	$ 324,183	$ 311,332
CH2M HILL Companies, Ltd. \| Write off of Deferred Tax Asset
Restructuring Cost and Reserve [Line Items]
Restructuring charges	10,000
CH2M HILL Companies, Ltd. \| Continuing Operations
Restructuring Cost and Reserve [Line Items]
Restructuring charges	99,590	324,183	311,470
CH2M HILL Companies, Ltd. \| Other Expense \| Other
Restructuring Cost and Reserve [Line Items]
Gain (loss) on litigation settlement	(2,100)		35,000
CH2M HILL Companies, Ltd. \| Other Expense \| Continuing Operations
Restructuring Cost and Reserve [Line Items]
Restructuring charges	61,000	321,600	337,000
CH2M HILL Companies, Ltd. \| Operating Segments \| Critical Mission Solutions
Restructuring Cost and Reserve [Line Items]
Restructuring charges	5,079	24,083	17,989
CH2M HILL Companies, Ltd. \| Operating Segments \| People & Places Solutions
Restructuring Cost and Reserve [Line Items]
Restructuring charges	7,077	170,631	108,835
CH2M HILL Companies, Ltd. \| Operating Segments \| PA Consulting
Restructuring Cost and Reserve [Line Items]
Restructuring charges	15,566	0	0
CH2M HILL Companies, Ltd. \| Operating Segments \| Energy, Chemicals and Resources (included in Discontinued Operations)
Restructuring Cost and Reserve [Line Items]
Restructuring charges	0	0	138
CH2M HILL Companies, Ltd. \| Corporate
Restructuring Cost and Reserve [Line Items]
Restructuring charges	$ 71,868	$ 129,469	$ 184,646