Segment Disclosures - Segment Revenue Per Service (Details) - Service - USD ($) $ in Millions	12 Months Ended
	Jan. 03, 2021	Dec. 29, 2019	Dec. 30, 2018
Segment Reporting, Revenue Reconciling Item [Line Items]
Segment revenue from services	$ 4,516.0	$ 5,355.6	$ 5,513.9
Less: Intersegment revenue
Segment Reporting, Revenue Reconciling Item [Line Items]
Segment revenue from services	(0.5)	(0.5)	(0.4)
Professional & Industrial | Reporting Segments
Segment Reporting, Revenue Reconciling Item [Line Items]
Segment revenue from services	1,858.4	2,213.4	2,430.9
Science, Engineering & Technology | Reporting Segments
Segment Reporting, Revenue Reconciling Item [Line Items]
Segment revenue from services	1,019.1	1,131.8	1,002.6
Education | Reporting Segments
Segment Reporting, Revenue Reconciling Item [Line Items]
Segment revenue from services	286.9	450.7	428.5
Outsourcing & Consulting | Reporting Segments
Segment Reporting, Revenue Reconciling Item [Line Items]
Segment revenue from services	363.5	377.7	377.1
International | Reporting Segments
Segment Reporting, Revenue Reconciling Item [Line Items]
Segment revenue from services	$ 988.6	$ 1,182.5	$ 1,275.2