Revenue - Narrative (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 28, 2020	Jun. 30, 2019	Jun. 28, 2020	Jun. 30, 2019	Dec. 29, 2019
Revenue from Contract with Customer [Line Items]
Revenue	$ 975.3	$ 1,367.5	$ 2,236.4	$ 2,750.1
Americas
Revenue from Contract with Customer [Line Items]
Revenue	774.3	1,082.0	1,791.1	2,189.1
Americas | Global Talent Solutions
Revenue from Contract with Customer [Line Items]
Revenue	450.5	488.4	937.0	972.8
EMEA
Revenue from Contract with Customer [Line Items]
Revenue	194.2	278.9	431.8	548.9
EMEA | Global Talent Solutions
Revenue from Contract with Customer [Line Items]
Revenue	9.5	10.9	19.5	22.0
Deferred Sales Commissions
Revenue from Contract with Customer [Line Items]
Capitalized contract cost	1.1		1.1		$ 1.5
Capitalized contract cost, amortization	0.3	0.4	0.6	0.9
Deferred Fulfillment Costs
Revenue from Contract with Customer [Line Items]
Capitalized contract cost	3.4		3.4		$ 3.6
Capitalized contract cost, amortization	$ 4.8	$ 3.1	$ 9.6	$ 6.5