Revenue - Disaggregation of Revenues by Geographic Region (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Oct. 03, 2021	Sep. 27, 2020	Oct. 03, 2021	Sep. 27, 2020
Disaggregation of Revenue [Line Items]
Revenue	$ 1,195.4	$ 1,038.2	$ 3,659.4	$ 3,274.6
Americas
Disaggregation of Revenue [Line Items]
Revenue	934.9	818.5	2,880.4	2,609.6
Asia-Pacific
Disaggregation of Revenue [Line Items]
Revenue	10.7	7.6	28.3	21.1
Science, Engineering & Technology
Disaggregation of Revenue [Line Items]
Revenue	306.2	244.0	859.1	761.5
Science, Engineering & Technology | Americas
Disaggregation of Revenue [Line Items]
Revenue	304.3	242.8	854.1	757.3
Science, Engineering & Technology | Europe
Disaggregation of Revenue [Line Items]
Revenue	1.9	1.2	5.0	4.2
Outsourcing & Consulting
Disaggregation of Revenue [Line Items]
Revenue	113.4	87.9	320.0	261.0
Outsourcing & Consulting | Americas
Disaggregation of Revenue [Line Items]
Revenue	97.5	72.9	274.9	215.9
Outsourcing & Consulting | Europe
Disaggregation of Revenue [Line Items]
Revenue	5.2	7.4	16.8	24.0
Outsourcing & Consulting | Asia-Pacific
Disaggregation of Revenue [Line Items]
Revenue	10.7	7.6	28.3	21.1
International
Disaggregation of Revenue [Line Items]
Revenue	256.8	232.4	810.1	710.6
International | Americas
Disaggregation of Revenue [Line Items]
Revenue	14.1	28.9	81.2	94.9
International | Europe
Disaggregation of Revenue [Line Items]
Revenue	$ 242.7	$ 203.5	$ 728.9	$ 615.7