Revenue - Disaggregation of Revenues by Service Type (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 29, 2025	Jun. 30, 2024	Jun. 29, 2025	Jun. 30, 2024
Disaggregation of Revenue [Line Items]
Revenue	$ 1,101.8	$ 1,057.5	$ 2,266.7	$ 2,102.6
Reporting Segments
Disaggregation of Revenue [Line Items]
Revenue	1,102.8	1,058.0	2,268.2	2,103.6
Reporting Segments \| Enterprise Talent Management
Disaggregation of Revenue [Line Items]
Revenue	520.2	541.2	1,054.2	1,065.3
Reporting Segments \| Science, Engineering & Technology
Disaggregation of Revenue [Line Items]
Revenue	317.3	265.7	639.7	497.3
Reporting Segments \| Education
Disaggregation of Revenue [Line Items]
Revenue	265.3	251.1	574.3	541.0
Reporting Segments \| Staffing Services
Disaggregation of Revenue [Line Items]
Revenue	733.0	705.4	1,526.5	1,420.1
Reporting Segments \| Staffing Services \| Enterprise Talent Management
Disaggregation of Revenue [Line Items]
Revenue	269.6	292.2	550.3	578.1
Reporting Segments \| Staffing Services \| Science, Engineering & Technology
Disaggregation of Revenue [Line Items]
Revenue	200.7	164.7	405.6	304.7
Reporting Segments \| Staffing Services \| Education
Disaggregation of Revenue [Line Items]
Revenue	262.7	248.5	570.6	537.3
Reporting Segments \| Outcome-based Services
Disaggregation of Revenue [Line Items]
Revenue	228.1	224.0	470.7	442.2
Reporting Segments \| Outcome-based Services \| Enterprise Talent Management
Disaggregation of Revenue [Line Items]
Revenue	120.8	128.8	254.0	259.6
Reporting Segments \| Outcome-based Services \| Science, Engineering & Technology
Disaggregation of Revenue [Line Items]
Revenue	107.3	95.2	216.7	182.6
Reporting Segments \| Outcome-based Services \| Education
Disaggregation of Revenue [Line Items]
Revenue	0.0	0.0	0.0	0.0
Reporting Segments \| Talent Solutions
Disaggregation of Revenue [Line Items]
Revenue	126.9	117.9	244.7	222.6
Reporting Segments \| Talent Solutions \| Enterprise Talent Management
Disaggregation of Revenue [Line Items]
Revenue	126.9	117.9	244.7	222.6
Reporting Segments \| Talent Solutions \| Science, Engineering & Technology
Disaggregation of Revenue [Line Items]
Revenue	0.0	0.0	0.0	0.0
Reporting Segments \| Talent Solutions \| Education
Disaggregation of Revenue [Line Items]
Revenue	0.0	0.0	0.0	0.0
Reporting Segments \| Permanent Placement
Disaggregation of Revenue [Line Items]
Revenue	14.8	10.7	26.3	18.7
Reporting Segments \| Permanent Placement \| Enterprise Talent Management
Disaggregation of Revenue [Line Items]
Revenue	2.9	2.3	5.2	5.0
Reporting Segments \| Permanent Placement \| Science, Engineering & Technology
Disaggregation of Revenue [Line Items]
Revenue	9.3	5.8	17.4	10.0
Reporting Segments \| Permanent Placement \| Education
Disaggregation of Revenue [Line Items]
Revenue	2.6	2.6	3.7	3.7
Intersegment
Disaggregation of Revenue [Line Items]
Revenue	$ (1.0)	$ (0.5)	$ (1.5)	$ (1.0)