Revenue - Disaggregation of Revenues by Service Type (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 28, 2026	Jun. 29, 2025	Jun. 28, 2026	Jun. 29, 2025
Disaggregation of Revenue [Line Items]
Revenue	$ 1,038.2	$ 1,101.8	$ 2,078.9	$ 2,266.7
Reporting Segments
Disaggregation of Revenue [Line Items]
Revenue	1,040.6	1,102.8	2,083.1	2,268.2
Reporting Segments \| Enterprise Talent Management
Disaggregation of Revenue [Line Items]
Revenue	485.5	516.4	944.7	1,045.5
Reporting Segments \| Science, Engineering & Technology
Disaggregation of Revenue [Line Items]
Revenue	301.6	321.1	590.8	648.4
Reporting Segments \| Education
Disaggregation of Revenue [Line Items]
Revenue	253.5	265.3	547.6	574.3
Reporting Segments \| Staffing Services
Disaggregation of Revenue [Line Items]
Revenue	663.7	733.0	1,355.0	1,526.5
Reporting Segments \| Staffing Services \| Enterprise Talent Management
Disaggregation of Revenue [Line Items]
Revenue	239.3	265.8	468.6	541.6
Reporting Segments \| Staffing Services \| Science, Engineering & Technology
Disaggregation of Revenue [Line Items]
Revenue	172.9	204.5	341.5	414.3
Reporting Segments \| Staffing Services \| Education
Disaggregation of Revenue [Line Items]
Revenue	251.5	262.7	544.9	570.6
Reporting Segments \| Outcome-based Services
Disaggregation of Revenue [Line Items]
Revenue	228.3	228.1	447.3	470.7
Reporting Segments \| Outcome-based Services \| Enterprise Talent Management
Disaggregation of Revenue [Line Items]
Revenue	109.6	120.8	216.4	254.0
Reporting Segments \| Outcome-based Services \| Science, Engineering & Technology
Disaggregation of Revenue [Line Items]
Revenue	118.7	107.3	230.9	216.7
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	134.9	126.9	256.2	244.7
Reporting Segments \| Talent Solutions \| Enterprise Talent Management
Disaggregation of Revenue [Line Items]
Revenue	134.9	126.9	256.2	244.7
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	13.7	14.8	24.6	26.3
Reporting Segments \| Permanent Placement \| Enterprise Talent Management
Disaggregation of Revenue [Line Items]
Revenue	1.7	2.9	3.5	5.2
Reporting Segments \| Permanent Placement \| Science, Engineering & Technology
Disaggregation of Revenue [Line Items]
Revenue	10.0	9.3	18.4	17.4
Reporting Segments \| Permanent Placement \| Education
Disaggregation of Revenue [Line Items]
Revenue	2.0	2.6	2.7	3.7
Intersegment
Disaggregation of Revenue [Line Items]
Revenue	$ (2.4)	$ (1.0)	$ (4.2)	$ (1.5)