Business Combinations - Narrative (Details) - USD ($) $ / shares in Units, shares in Millions		4 Months Ended	6 Months Ended	15 Months Ended
	Dec. 15, 2017	Mar. 30, 2018	Mar. 29, 2019	Dec. 28, 2018	Apr. 21, 2019	Sep. 28, 2018
Business Acquisition [Line Items]
Common stock, par value (in dollars per share)			$ 1			$ 1
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
Long-term debt	$ 706,000,000
Goodwill recognized expected to be deductible for tax purposes	0
Business Combination, Provisional Information, Initial Accounting Incomplete, Adjustment, Financial Liabilities	404,700,000
Decrease in receivables				$ 4,000,000
Increase in accrued liabilities				11,500,000
Increase in miscellaneous long-term assets				20,700,000
Goodwill increase in the period				$ 28,100,000
Revenue of acquiree since acquisition date, actual		$ 1,300,000,000
Earnings of acquiree since acquisition date, actual		6,500,000
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			10 years
CH2M HILL Companies, Ltd. | Customer relationships, contracts and backlog | Minimum
Business Acquisition [Line Items]
Finite-lived intangible asset, useful life			9 years
CH2M HILL Companies, Ltd. | Customer relationships, contracts and backlog | Maximum
Business Acquisition [Line Items]
Finite-lived intangible asset, useful life			11 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
Long-term debt	$ 700,000,000
Subsequent Event | KeyW Holding Corporation
Business Acquisition [Line Items]
Common stock, par value (in dollars per share)					$ 0.001
Acquisition share price (in dollars per share)					$ 11.25