Revenue - Disaggregation of Revenues by Service Type (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jul. 03, 2022	Jul. 04, 2021	Jul. 03, 2022	Jul. 04, 2021
Disaggregation of Revenue [Line Items]
Revenue	$ 1,267.3	$ 1,258.1	$ 2,563.7	$ 2,464.0
Professional & Industrial
Disaggregation of Revenue [Line Items]
Revenue	415.8	466.5	860.1	934.1
Science, Engineering & Technology
Disaggregation of Revenue [Line Items]
Revenue	324.3	298.2	641.4	552.9
Education
Disaggregation of Revenue [Line Items]
Revenue	155.5	105.9	328.9	217.5
Outsourcing & Consulting
Disaggregation of Revenue [Line Items]
Revenue	124.4	107.3	233.5	206.6
International
Disaggregation of Revenue [Line Items]
Revenue	247.6	280.4	500.4	553.3
Staffing services | Professional & Industrial
Disaggregation of Revenue [Line Items]
Revenue	309.5	359.8	644.4	712.3
Staffing services | Science, Engineering & Technology
Disaggregation of Revenue [Line Items]
Revenue	223.1	212.9	443.7	399.1
Staffing services | Education
Disaggregation of Revenue [Line Items]
Revenue	152.5	104.1	324.4	214.9
Staffing services | International
Disaggregation of Revenue [Line Items]
Revenue	237.2	272.0	478.9	537.6
Permanent placement | Professional & Industrial
Disaggregation of Revenue [Line Items]
Revenue	7.7	5.3	17.9	10.2
Permanent placement | Science, Engineering & Technology
Disaggregation of Revenue [Line Items]
Revenue	8.5	6.1	16.5	10.9
Permanent placement | Education
Disaggregation of Revenue [Line Items]
Revenue	3.0	1.8	4.5	2.6
Permanent placement | International
Disaggregation of Revenue [Line Items]
Revenue	5.6	5.4	12.5	10.9
Outcome-based services | Professional & Industrial
Disaggregation of Revenue [Line Items]
Revenue	98.6	101.4	197.8	211.6
Outcome-based services | Science, Engineering & Technology
Disaggregation of Revenue [Line Items]
Revenue	92.7	79.2	181.2	142.9
Talent solutions | Outsourcing & Consulting
Disaggregation of Revenue [Line Items]
Revenue	124.4	107.3	233.5	206.6
Talent solutions | International
Disaggregation of Revenue [Line Items]
Revenue	4.8	3.0	9.0	4.8
Total Intersegment
Disaggregation of Revenue [Line Items]
Revenue	$ (0.3)	$ (0.2)	$ (0.6)	$ (0.4)