Goodwill and Other Intangible Assets - Schedule of Goodwill Balances by Reporting Unit (Details) - USD ($) $ in Millions	Sep. 30, 2019	Apr. 03, 2019	Dec. 31, 2018
Goodwill [Line Items]
Goodwill	$ 1,231.8		$ 1,297.1
Jefferson Wells
Goodwill [Line Items]
Goodwill	55.5
Americas | United States
Goodwill [Line Items]
Goodwill	485.2		476.5
Americas | United States | Jefferson Wells
Goodwill [Line Items]
Goodwill	540.7		532.0
Northern Europe | Netherlands
Goodwill [Line Items]
Goodwill	106.5		112.0
Northern Europe | United Kingdom
Goodwill [Line Items]
Goodwill	90.2		93.7
Northern Europe | Germany
Goodwill [Line Items]
Goodwill	64.8		129.2
Southern Europe
Goodwill [Line Items]
Goodwill		$ 33.8
Southern Europe | France
Goodwill [Line Items]
Goodwill	65.5		68.9
Other Reporting Units
Goodwill [Line Items]
Goodwill	302.0		299.2
Reportable segments | Americas
Goodwill [Line Items]
Goodwill	529.9		519.9
Reportable segments | Northern Europe
Goodwill [Line Items]
Goodwill	356.3		435.4
Reportable segments | Southern Europe
Goodwill [Line Items]
Goodwill	140.9		112.2
Reportable segments | Right Management
Goodwill [Line Items]
Goodwill	$ 62.1		$ 62.1