Segment Disclosures - Segment Revenue From Service (Details) - Service - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Jul. 01, 2018	Jun. 30, 2019	Jul. 01, 2018
Revenue from Services
Segment revenue from services	$ 1,367.5	$ 1,386.9	$ 2,750.1	$ 2,756.8
Less: Intersegment revenue
Revenue from Services
Segment revenue from services	(4.1)	(4.4)	(7.9)	(9.3)
Americas Staffing | Reporting Segments
Revenue from Services
Segment revenue from services	597.6	604.0	1,224.1	1,208.3
Global Talent Solutions | Reporting Segments
Revenue from Services
Segment revenue from services	505.9	500.7	1,006.9	986.5
International Staffing | Reporting Segments
Revenue from Services
Segment revenue from services	$ 268.1	$ 286.6	$ 527.0	$ 571.3