Goodwill and Other Intangible Assets - Schedule of Goodwill Balances by Reporting Unit (Details) - USD ($) $ in Millions	Jun. 30, 2020	Dec. 31, 2019
Goodwill [Line Items]
Goodwill	$ 1,178.2	$ 1,260.1
Jefferson Wells
Goodwill [Line Items]
Goodwill	55.5
Americas | United States
Goodwill [Line Items]
Goodwill	490.2	490.3
Americas | United States | Jefferson Wells
Goodwill [Line Items]
Goodwill	545.7	545.8
Northern Europe | Netherlands
Goodwill [Line Items]
Goodwill	109.7	109.5
Northern Europe | United Kingdom
Goodwill [Line Items]
Goodwill	90.9	97.3
Northern Europe | Germany
Goodwill [Line Items]
Goodwill		67.2
Southern Europe | France
Goodwill [Line Items]
Goodwill	67.4	67.3
Other Reporting Units
Goodwill [Line Items]
Goodwill	302.4	310.9
Reportable segments | Americas
Goodwill [Line Items]
Goodwill	533.4	535.6
Reportable segments | Northern Europe
Goodwill [Line Items]
Goodwill	296.8	374.6
Reportable segments | Southern Europe
Goodwill [Line Items]
Goodwill	144.8	144.8
Reportable segments | Right Management
Goodwill [Line Items]
Goodwill	$ 62.1	$ 62.1