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Segment Disclosures - Segment Earnings from Operations (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
Segment Reporting, Reconciling Item for Operating Profit (Loss) from Segment to Consolidated [Line Items]
Gross profit	$ 245.1	$ 227.7	$ 244.0	$ 251.6	$ 254.4	$ 239.1	$ 240.5	$ 238.2	$ 968.4	$ 972.2	$ 954.1
SG&A expenses	(216.2)	(210.6)	(221.5)	(234.8)	(221.3)	(217.2)	(220.1)	(226.2)	(883.1)	(884.8)	(870.8)
Earnings from operations									81.8	87.4	83.3
Gain (loss) on investment in Persol Holdings	$ 0.7	$ (39.3)	$ 61.2	$ 13.2	$ (83.2)	$ 15.8	$ (52.5)	$ 23.7	35.8	(96.2)	0.0
Other expense, net									(1.2)	(0.6)	(1.6)
Earnings (loss) before taxes and equity in net earnings (loss) of affiliate									116.4	(9.4)	81.7
Reporting Segments \| Americas Staffing
Segment Reporting, Reconciling Item for Operating Profit (Loss) from Segment to Consolidated [Line Items]
Gross profit									429.5	441.3	429.1
SG&A expenses									(372.7)	(364.2)	(346.4)
Earnings from operations									56.8	77.1	82.7
Reporting Segments \| GTS
Segment Reporting, Reconciling Item for Operating Profit (Loss) from Segment to Consolidated [Line Items]
Gross profit									400.5	381.1	373.7
SG&A expenses									(293.1)	(296.5)	(296.7)
Earnings from operations									107.4	84.6	77.0
Reporting Segments \| International Staffing
Segment Reporting, Reconciling Item for Operating Profit (Loss) from Segment to Consolidated [Line Items]
Gross profit									140.5	152.3	153.7
SG&A expenses									(125.3)	(132.3)	(131.6)
Earnings from operations									15.2	20.0	22.1
Intersegment Eliminations
Segment Reporting, Reconciling Item for Operating Profit (Loss) from Segment to Consolidated [Line Items]
Gross profit									(2.1)	(2.5)	(2.4)
SG&A expenses									2.1	2.5	2.4
Earnings from operations									0.0	0.0	0.0
Corporate
Segment Reporting, Reconciling Item for Operating Profit (Loss) from Segment to Consolidated [Line Items]
Earnings from operations									$ (97.6)	$ (94.3)	$ (98.5)