Segment Disclosures - Segment Revenue From Service (Details) - Service - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 28, 2020	Jun. 30, 2019	Jun. 28, 2020	Jun. 30, 2019
Revenue from Services
Segment revenue from services	$ 975.3	$ 1,367.5	$ 2,236.4	$ 2,750.1
Less: Intersegment revenue
Revenue from Services
Segment revenue from services	(2.9)	(4.1)	(6.0)	(7.9)
Americas Staffing | Reporting Segments
Revenue from Services
Segment revenue from services	326.7	597.6	860.1	1,224.1
Global Talent Solutions | Reporting Segments
Revenue from Services
Segment revenue from services	466.9	505.9	970.1	1,006.9
International Staffing | Reporting Segments
Revenue from Services
Segment revenue from services	$ 184.6	$ 268.1	$ 412.2	$ 527.0