Segment Disclosures - Segment Revenue Per Service (Details) - USD ($) $ in Millions	3 Months Ended								12 Months Ended
	Dec. 29, 2019	Sep. 29, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 30, 2018	Sep. 30, 2018	Jul. 01, 2018	Apr. 01, 2018	Dec. 29, 2019	Dec. 30, 2018	Dec. 31, 2017
Revenues [Abstract]
Revenue from services	$ 1,337.8	$ 1,267.7	$ 1,367.5	$ 1,382.6	$ 1,414.7	$ 1,342.4	$ 1,386.9	$ 1,369.9	$ 5,355.6	$ 5,513.9
Service
Revenues [Abstract]
Revenue from services									5,355.6	5,513.9	$ 5,374.4
Service | Reporting Segments | Americas Staffing
Revenues [Abstract]
Revenue from services									2,320.1	2,417.7	2,345.9
Service | Reporting Segments | GTS
Revenues [Abstract]
Revenue from services									2,024.5	1,997.4	1,998.9
Service | Reporting Segments | International Staffing
Revenues [Abstract]
Revenue from services									1,025.9	1,116.6	1,048.2
Service | Intersegment Eliminations
Revenues [Abstract]
Revenue from services									$ (14.9)	$ (17.8)	$ (18.6)