Revenue - Disaggregation of Revenues by Service Type (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 27, 2026	Sep. 28, 2025	Sep. 27, 2026	Sep. 28, 2025
Disaggregation of Revenue [Line Items]
Revenue	$ 927.2	$ 935.0	$ 3,006.1	$ 3,201.7
Reporting Segments
Disaggregation of Revenue [Line Items]
Revenue	932.4	936.1	3,015.5	3,204.3
Reporting Segments \| Enterprise Talent Management
Disaggregation of Revenue [Line Items]
Revenue	496.1	484.5	1,440.8	1,530.0
Reporting Segments \| Science, Engineering & Technology
Disaggregation of Revenue [Line Items]
Revenue	302.1	308.3	892.9	956.7
Reporting Segments \| Education
Disaggregation of Revenue [Line Items]
Revenue	134.2	143.3	681.8	717.6
Reporting Segments \| Staffing Services
Disaggregation of Revenue [Line Items]
Revenue	546.6	584.4	1,901.6	2,110.9
Reporting Segments \| Staffing Services \| Enterprise Talent Management
Disaggregation of Revenue [Line Items]
Revenue	243.8	246.7	712.4	788.3
Reporting Segments \| Staffing Services \| Science, Engineering & Technology
Disaggregation of Revenue [Line Items]
Revenue	169.9	195.2	511.4	609.5
Reporting Segments \| Staffing Services \| Education
Disaggregation of Revenue [Line Items]
Revenue	132.9	142.5	677.8	713.1
Reporting Segments \| Outcome-based Services
Disaggregation of Revenue [Line Items]
Revenue	229.6	212.8	676.9	683.5
Reporting Segments \| Outcome-based Services \| Enterprise Talent Management
Disaggregation of Revenue [Line Items]
Revenue	107.8	108.5	324.2	362.5
Reporting Segments \| Outcome-based Services \| Science, Engineering & Technology
Disaggregation of Revenue [Line Items]
Revenue	121.8	104.3	352.7	321.0
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	142.0	127.2	398.2	371.9
Reporting Segments \| Talent Solutions \| Enterprise Talent Management
Disaggregation of Revenue [Line Items]
Revenue	142.0	127.2	398.2	371.9
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	14.2	11.7	38.8	38.0
Reporting Segments \| Permanent Placement \| Enterprise Talent Management
Disaggregation of Revenue [Line Items]
Revenue	2.5	2.1	6.0	7.3
Reporting Segments \| Permanent Placement \| Science, Engineering & Technology
Disaggregation of Revenue [Line Items]
Revenue	10.4	8.8	28.8	26.2
Reporting Segments \| Permanent Placement \| Education
Disaggregation of Revenue [Line Items]
Revenue	1.3	0.8	4.0	4.5
Intersegment
Disaggregation of Revenue [Line Items]
Revenue	$ (5.2)	$ (1.1)	$ (9.4)	$ (2.6)