Revenue - Disaggregation of Revenues (Details) - USD ($) $ in Millions	3 Months Ended
	Apr. 01, 2018	Apr. 02, 2017
Disaggregation of Revenue [Line Items]
Revenue	$ 1,369.9	$ 1,289.7
Outcome-Based Services
Disaggregation of Revenue [Line Items]
Revenue	116.2
Global Talent Solutions
Disaggregation of Revenue [Line Items]
Revenue	485.8
Americas Staffing
Disaggregation of Revenue [Line Items]
Revenue	604.3
International Staffing
Disaggregation of Revenue [Line Items]
Revenue	284.7
Talent Fulfillment
Disaggregation of Revenue [Line Items]
Revenue	369.6
Commercial | Americas Staffing
Disaggregation of Revenue [Line Items]
Revenue	398.4
Educational Staffing | Americas Staffing
Disaggregation of Revenue [Line Items]
Revenue	130.1
PT | Americas Staffing
Disaggregation of Revenue [Line Items]
Revenue	67.4
Permanent Placement | Americas Staffing
Disaggregation of Revenue [Line Items]
Revenue	8.4
Permanent Placement | International Staffing
Disaggregation of Revenue [Line Items]
Revenue	7.8
Permanent Placement | Talent Fulfillment
Disaggregation of Revenue [Line Items]
Revenue	0.4
Staffing Solutions | International Staffing
Disaggregation of Revenue [Line Items]
Revenue	276.9
Staffing Solutions | Talent Fulfillment
Disaggregation of Revenue [Line Items]
Revenue	284.2
Talent Solutions | Talent Fulfillment
Disaggregation of Revenue [Line Items]
Revenue	85.0
Less: Intersegment
Disaggregation of Revenue [Line Items]
Revenue	$ (4.9)