Revenue - Disaggregation of Revenues (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 29, 2020	Mar. 31, 2019
Disaggregation of Revenue [Line Items]
Revenue	$ 1,261.1	$ 1,382.6
Outcome-Based Services
Disaggregation of Revenue [Line Items]
Revenue	172.2	155.4
Global Talent Solutions
Disaggregation of Revenue [Line Items]
Revenue	503.2	501.0
Americas Staffing
Disaggregation of Revenue [Line Items]
Revenue	533.4	626.5
International Staffing
Disaggregation of Revenue [Line Items]
Revenue	227.6	258.9
Talent Fulfillment
Disaggregation of Revenue [Line Items]
Revenue	331.0	345.6
Commercial | Americas Staffing
Disaggregation of Revenue [Line Items]
Revenue	308.5	392.5
Education | Americas Staffing
Disaggregation of Revenue [Line Items]
Revenue	143.1	139.6
Professional/Technical | Americas Staffing
Disaggregation of Revenue [Line Items]
Revenue	75.4	85.5
Permanent Placement | Americas Staffing
Disaggregation of Revenue [Line Items]
Revenue	6.4	8.9
Permanent Placement | International Staffing
Disaggregation of Revenue [Line Items]
Revenue	5.7	6.7
Permanent Placement | Talent Fulfillment
Disaggregation of Revenue [Line Items]
Revenue	0.3	0.3
Staffing Solutions | International Staffing
Disaggregation of Revenue [Line Items]
Revenue	221.9	252.2
Staffing Solutions | Talent Fulfillment
Disaggregation of Revenue [Line Items]
Revenue	244.5	255.6
Talent Solutions | Talent Fulfillment
Disaggregation of Revenue [Line Items]
Revenue	86.2	89.7
Less: Intersegment
Disaggregation of Revenue [Line Items]
Revenue	$ (3.1)	$ (3.8)