Segment Information - Schedule of Total Revenues, Segment Operating Profit and Total Asset for Reporting Segment (Details) - USD ($)	3 Months Ended		6 Months Ended
	Mar. 30, 2018	Mar. 31, 2017	Mar. 30, 2018	Mar. 31, 2017
Segment Reporting Information [Line Items]
Revenues from External Customers	$ 3,935,028,000	$ 2,302,567,000	$ 6,685,338,000	$ 4,854,171,000
Total Segment Operating Profit	146,286,000	68,173,000	193,929,000	156,801,000
Restructuring and Other Charges	(68,885,000)	(72,225,000)	(88,234,000)	(103,966,000)
Total Other (Expense) Income, net	(24,119,000)	(7,682,000)	(29,846,000)	(10,430,000)
Earnings Before Taxes	122,167,000	60,491,000	164,083,000	146,371,000
Restructuring charges excluded segment profit			88,701,000
CH2M HILL Companies, Ltd.
Segment Reporting Information [Line Items]
CH2M Transaction Costs	(4,852,000)	0	(72,493,000)	0
Restructuring charges excluded segment profit	69,351,000	52,266,000	88,701,000	84,007,000
Operating Segments
Segment Reporting Information [Line Items]
Total Segment Operating Profit	255,683,000	148,736,000	432,445,000	287,401,000
Corporate
Segment Reporting Information [Line Items]
Other Corporate Expenses	(35,660,000)	(8,338,000)	(77,789,000)	(26,634,000)
Corporate | CH2M HILL Companies, Ltd.
Segment Reporting Information [Line Items]
Restructuring charges excluded segment profit	57,243,000	20,362,000	69,768,000	27,917,000
Aerospace, Technology, Environmental and Nuclear
Segment Reporting Information [Line Items]
Revenues from External Customers	1,105,673,000	602,043,000	1,851,594,000	1,205,228,000
Aerospace, Technology, Environmental and Nuclear | Operating Segments
Segment Reporting Information [Line Items]
Revenues from External Customers	1,105,673,000	602,043,000	1,851,594,000	1,205,228,000
Total Segment Operating Profit	61,338,000	44,341,000	127,669,000	94,397,000
Litigation expenses included in segment profit	17,300,000		17,300,000
Aerospace, Technology, Environmental and Nuclear | Operating Segments | CH2M HILL Companies, Ltd.
Segment Reporting Information [Line Items]
Restructuring charges excluded segment profit	1,409,000	1,274,000	1,722,000	1,646,000
Buildings, Infrastructure and Advanced Facilities
Segment Reporting Information [Line Items]
Revenues from External Customers	1,758,412,000	897,829,000	2,790,177,000	1,836,723,000
Buildings, Infrastructure and Advanced Facilities | Operating Segments
Segment Reporting Information [Line Items]
Revenues from External Customers	1,758,412,000	897,829,000	2,790,177,000	1,836,723,000
Total Segment Operating Profit	138,017,000	63,342,000	201,986,000	118,690,000
Restructuring charges excluded segment profit	22,600,000		22,600,000
Buildings, Infrastructure and Advanced Facilities | Operating Segments | CH2M HILL Companies, Ltd.
Segment Reporting Information [Line Items]
Restructuring charges excluded segment profit	18,287,000	9,996,000	21,178,000	18,002,000
Energy, Chemicals and Resources
Segment Reporting Information [Line Items]
Revenues from External Customers	1,070,943,000	802,695,000	2,043,567,000	1,812,220,000
Energy, Chemicals and Resources | Operating Segments
Segment Reporting Information [Line Items]
Revenues from External Customers	1,070,943,000	802,695,000	2,043,567,000	1,812,220,000
Total Segment Operating Profit	56,328,000	41,053,000	102,790,000	74,314,000
Energy, Chemicals and Resources | Operating Segments | CH2M HILL Companies, Ltd.
Segment Reporting Information [Line Items]
Restructuring charges excluded segment profit	(7,588,000)	$ 20,634,000	(3,967,000)	$ 36,442,000
Other Expense | CH2M HILL Companies, Ltd.
Segment Reporting Information [Line Items]
Amortization of deferred financing fees	$ 466,000		$ 722,000