Revenue - Disaggregation of Revenues by Service Type (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 29, 2024	Dec. 31, 2023	Jan. 01, 2023
Disaggregation of Revenue [Line Items]
Revenue from services	$ 4,331.8	$ 4,835.7	$ 4,965.4
Science, Engineering & Technology
Disaggregation of Revenue [Line Items]
Revenue from services	1,422.8	1,190.8	1,265.4
Outsourcing & Consulting
Disaggregation of Revenue [Line Items]
Revenue from services	468.3	454.7	468.0
International
Disaggregation of Revenue [Line Items]
Revenue from services	0.0	812.1	887.0
Intersegment Eliminations
Disaggregation of Revenue [Line Items]
Revenue from services	(2.3)	(3.3)	(1.1)
Reporting Segments | Professional & Industrial
Disaggregation of Revenue [Line Items]
Revenue from services	1,470.7	1,539.5	1,709.9
Reporting Segments | Professional & Industrial | Staffing services
Disaggregation of Revenue [Line Items]
Revenue from services	956.9	1,014.2	1,229.5
Reporting Segments | Professional & Industrial | Permanent placement
Disaggregation of Revenue [Line Items]
Revenue from services	9.7	14.0	30.3
Reporting Segments | Professional & Industrial | Outcome-based services
Disaggregation of Revenue [Line Items]
Revenue from services	504.1	511.3	450.1
Reporting Segments | Science, Engineering & Technology
Disaggregation of Revenue [Line Items]
Revenue from services	1,422.8	1,190.8	1,265.4
Reporting Segments | Science, Engineering & Technology | Staffing services
Disaggregation of Revenue [Line Items]
Revenue from services	945.3	792.7	869.0
Reporting Segments | Science, Engineering & Technology | Permanent placement
Disaggregation of Revenue [Line Items]
Revenue from services	29.5	17.8	29.7
Reporting Segments | Science, Engineering & Technology | Outcome-based services
Disaggregation of Revenue [Line Items]
Revenue from services	421.5	380.3	366.7
Reporting Segments | Science, Engineering & Technology | Talent solutions
Disaggregation of Revenue [Line Items]
Revenue from services	26.5	0.0	0.0
Reporting Segments | Education
Disaggregation of Revenue [Line Items]
Revenue from services	972.3	841.9	636.2
Reporting Segments | Education | Staffing services
Disaggregation of Revenue [Line Items]
Revenue from services	966.0	834.9	627.8
Reporting Segments | Education | Permanent placement
Disaggregation of Revenue [Line Items]
Revenue from services	6.3	7.0	8.4
Reporting Segments | Outsourcing & Consulting
Disaggregation of Revenue [Line Items]
Revenue from services	468.3	454.7	468.0
Reporting Segments | Outsourcing & Consulting | Talent solutions
Disaggregation of Revenue [Line Items]
Revenue from services	468.3	454.7	468.0
Reporting Segments | International
Disaggregation of Revenue [Line Items]
Revenue from services	0.0	812.1	887.0
Reporting Segments | International | Staffing services
Disaggregation of Revenue [Line Items]
Revenue from services	0.0	790.0	851.4
Reporting Segments | International | Permanent placement
Disaggregation of Revenue [Line Items]
Revenue from services	0.0	20.7	21.2
Reporting Segments | International | Talent solutions
Disaggregation of Revenue [Line Items]
Revenue from services	$ 0.0	$ 1.4	$ 14.4