Segment Disclosures - Segment Revenue From Service (Details) - Service - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Oct. 01, 2017	Sep. 30, 2018	Oct. 01, 2017
Revenue from Services
Segment revenue from services	$ 1,342.4	$ 1,328.8	$ 4,099.2	$ 3,952.1
Less: Intersegment revenue
Revenue from Services
Segment revenue from services	(4.2)	(4.6)	(13.5)	(13.2)
Americas Staffing | Reporting Segments
Revenue from Services
Segment revenue from services	561.8	554.8	1,770.1	1,703.5
Global Talent Solutions | Reporting Segments
Revenue from Services
Segment revenue from services	507.6	503.0	1,494.1	1,495.8
International Staffing | Reporting Segments
Revenue from Services
Segment revenue from services	$ 277.2	$ 275.6	$ 848.5	$ 766.0