Business Combinations - Schedule of Transaction Costs Associated with Acquisition (Details) - CH2M HILL Companies, Ltd. - USD ($) $ in Millions	12 Months Ended
Sep. 28, 2018	Sep. 29, 2017
Business Acquisition [Line Items]
Personnel costs	$ 50.2	$ 2.2
Professional services and other expenses	27.5	14.9
Total	$ 77.7	$ 17.1

Costs incurred to effect a business combination which have been expensed during the period. Such costs could include business integration costs, systems integration and conversion costs, and severance and other employee-related costs.

No definition available.

Name:	us-gaap_BusinessCombinationIntegrationRelatedCosts
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration