Business Combinations - Schedule of Transaction Costs Associated with Acquisition (Details) - CH2M HILL Companies, Ltd. - USD ($) $ in Millions	3 Months Ended	6 Months Ended
Mar. 30, 2018	Mar. 30, 2018
Business Acquisition [Line Items]
Personnel costs	$ 4.7	$ 45.9
Professional services and other expenses	0.2	26.9
Total	$ 4.9	$ 72.8

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