Goodwill and Other Intangible Assets - Changes in Carrying Value of Goodwill by Reportable Segment (Parenthetical) (Details) - USD ($) $ in Millions		Jun. 30, 2022	Dec. 31, 2021
Goodwill [Roll Forward]
Goodwill	[1]	$ 1,669.9	$ 1,722.2
Jefferson Wells
Goodwill [Roll Forward]
Goodwill		55.5
Right Management
Goodwill [Roll Forward]
Goodwill		62.1
France
Goodwill [Roll Forward]
Goodwill		62.9	68.2
Americas | United States
Goodwill [Roll Forward]
Goodwill		1,008.3	1,013.0
Americas | United States | Jefferson Wells
Goodwill [Roll Forward]
Goodwill		1,087.0	1,091.7
Southern Europe | France
Goodwill [Roll Forward]
Goodwill		69.0	74.3
Southern Europe | Italy
Goodwill [Roll Forward]
Goodwill		$ 3.6	$ 3.9

[1] Balances were net of accumulated impairment loss of $644.2 as of both June 30, 2022 and December 31, 2021.