Business Combinations - Narrative (Details) - USD ($) shares in Millions			3 Months Ended	6 Months Ended
	Dec. 29, 2017	Dec. 15, 2017	Mar. 30, 2018	Mar. 30, 2018
Business Acquisition [Line Items]
Decrease in intangible assets				$ 151,957,000
Customer relationships, contracts and backlog
Business Acquisition [Line Items]
Decrease in intangible assets				$ 106,800,000
CH2M HILL Companies, Ltd.
Business Acquisition [Line Items]
Percentage of outstanding shares of common and preferred stock acquired		100.00%
Business combination consideration paid in cash		$ 1,800,000,000
Business combination, cash acquired		315,200,000
Business combination consideration equity issued		$ 1,400,000,000
Business combination consideration equity issued, shares		20.7
Business combination assumed revolving credit facility and second lien notes		$ 702,300,000
Goodwill recognized expected to be deductible for tax purposes		0
Decrease in intangible assets			$ 148,500,000
Decrease in property, plant and equipment			50,500,000
Decrease in amortization of intangible assets			$ (1,500,000)
Business combination assumed pensions and other long-term employee related liabilities included in deferred liabilities		291,000,000
Revenue contributed by acquiree from acquisition date	$ 1,300,000,000
Net earnings contributed by acquiree from acquisition date	(6,500,000)
Pre-tax restructuring and transaction costs	$ 78,000,000
CH2M HILL Companies, Ltd. | Customer relationships, contracts and backlog
Business Acquisition [Line Items]
Acquired finite-lived intangible assets, weighted average useful life				11 years
CH2M HILL Companies, Ltd. | Customer relationships, contracts and backlog | Minimum
Business Acquisition [Line Items]
Finite-lived intangible asset, useful life				10 years
CH2M HILL Companies, Ltd. | Customer relationships, contracts and backlog | Maximum
Business Acquisition [Line Items]
Finite-lived intangible asset, useful life				12 years
CH2M HILL Companies, Ltd. | Other Intangible Assets and Liabilities
Business Acquisition [Line Items]
Acquired finite-lived intangible assets, weighted average useful life				10 years
CH2M HILL Companies, Ltd. | Revolving Credit Facility and Second Lien Notes
Business Acquisition [Line Items]
Business combination prepayment penalty		20,000,000
Business combination assumed revolving credit facility and second lien notes		$ 700,000,000