Revenue - Disaggregation of Revenues by Service Type (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Oct. 02, 2022	Oct. 03, 2021	Oct. 02, 2022	Oct. 03, 2021
Disaggregation of Revenue [Line Items]
Revenue	$ 1,167.9	$ 1,195.4	$ 3,731.6	$ 3,659.4
Professional & Industrial
Disaggregation of Revenue [Line Items]
Revenue	408.6	452.6	1,268.7	1,386.7
Science, Engineering & Technology
Disaggregation of Revenue [Line Items]
Revenue	321.3	306.2	962.7	859.1
Education
Disaggregation of Revenue [Line Items]
Revenue	104.3	66.6	433.2	284.1
Outsourcing & Consulting
Disaggregation of Revenue [Line Items]
Revenue	118.5	113.4	352.0	320.0
International
Disaggregation of Revenue [Line Items]
Revenue	215.5	256.8	715.9	810.1
Staffing services | Professional & Industrial
Disaggregation of Revenue [Line Items]
Revenue	297.9	344.7	942.3	1,057.0
Staffing services | Science, Engineering & Technology
Disaggregation of Revenue [Line Items]
Revenue	220.6	214.0	664.3	613.1
Staffing services | Education
Disaggregation of Revenue [Line Items]
Revenue	103.0	65.7	427.4	280.6
Staffing services | International
Disaggregation of Revenue [Line Items]
Revenue	205.8	247.1	684.7	784.7
Permanent placement | Professional & Industrial
Disaggregation of Revenue [Line Items]
Revenue	6.1	6.9	24.0	17.1
Permanent placement | Science, Engineering & Technology
Disaggregation of Revenue [Line Items]
Revenue	7.1	6.5	23.6	17.4
Permanent placement | Education
Disaggregation of Revenue [Line Items]
Revenue	1.3	0.9	5.8	3.5
Permanent placement | International
Disaggregation of Revenue [Line Items]
Revenue	5.3	5.4	17.8	16.3
Outcome-based services | Professional & Industrial
Disaggregation of Revenue [Line Items]
Revenue	104.6	101.0	302.4	312.6
Outcome-based services | Science, Engineering & Technology
Disaggregation of Revenue [Line Items]
Revenue	93.6	85.7	274.8	228.6
Talent solutions | Outsourcing & Consulting
Disaggregation of Revenue [Line Items]
Revenue	118.5	113.4	352.0	320.0
Talent solutions | International
Disaggregation of Revenue [Line Items]
Revenue	4.4	4.3	13.4	9.1
Total Intersegment
Disaggregation of Revenue [Line Items]
Revenue	$ (0.3)	$ (0.2)	$ (0.9)	$ (0.6)