Revenue - Disaggregation of Revenues by Service Type (Details) - USD ($) $ in Millions	12 Months Ended
	Jan. 02, 2022	Jan. 03, 2021	Dec. 29, 2019
Disaggregation of Revenue [Line Items]
Revenue from services	$ 4,909.7	$ 4,516.0	$ 5,355.6
Professional & Industrial
Disaggregation of Revenue [Line Items]
Revenue from services	1,837.4	1,858.4	2,213.4
Science, Engineering & Technology
Disaggregation of Revenue [Line Items]
Revenue from services	1,156.8	1,019.1	1,131.8
Education
Disaggregation of Revenue [Line Items]
Revenue from services	416.5	286.9	450.7
Outsourcing & Consulting
Disaggregation of Revenue [Line Items]
Revenue from services	432.1	363.5	377.7
International
Disaggregation of Revenue [Line Items]
Revenue from services	1,067.8	988.6	1,182.5
Staffing services | Professional & Industrial
Disaggregation of Revenue [Line Items]
Revenue from services	1,402.4	1,423.3	1,838.6
Staffing services | Science, Engineering & Technology
Disaggregation of Revenue [Line Items]
Revenue from services	813.2	751.8	848.2
Staffing services | Education
Disaggregation of Revenue [Line Items]
Revenue from services	411.5	286.4	449.8
Staffing services | International
Disaggregation of Revenue [Line Items]
Revenue from services	1,032.9	971.8	1,156.8
Permanent Placement | Professional & Industrial
Disaggregation of Revenue [Line Items]
Revenue from services	24.7	9.9	17.9
Permanent Placement | Science, Engineering & Technology
Disaggregation of Revenue [Line Items]
Revenue from services	24.4	12.5	15.7
Permanent Placement | Education
Disaggregation of Revenue [Line Items]
Revenue from services	5.0	0.5	0.9
Permanent Placement | International
Disaggregation of Revenue [Line Items]
Revenue from services	21.3	16.8	25.7
Outcome-Based Services | Professional & Industrial
Disaggregation of Revenue [Line Items]
Revenue from services	410.3	425.2	356.9
Outcome-Based Services | Science, Engineering & Technology
Disaggregation of Revenue [Line Items]
Revenue from services	319.2	254.8	267.9
Talent Solutions | Outsourcing & Consulting
Disaggregation of Revenue [Line Items]
Revenue from services	432.1	363.5	377.7
Talent Solutions | International
Disaggregation of Revenue [Line Items]
Revenue from services	13.6	0.0	0.0
Intersegment Eliminations
Disaggregation of Revenue [Line Items]
Revenue from services	$ (0.9)	$ (0.5)	$ (0.5)