Goodwill and Other Intangible Assets - Changes in Carrying Value of Goodwill by Reportable Segment (Parenthetical) (Details) - USD ($) $ in Millions		Sep. 30, 2023	Dec. 31, 2022
Goodwill [Roll Forward]
Goodwill	[1]	$ 1,620.1	$ 1,628.1
Jefferson Wells
Goodwill [Roll Forward]
Goodwill		(55.5)	(55.5)
Right Management
Goodwill [Roll Forward]
Goodwill		(62.1)	(62.1)
France
Goodwill [Roll Forward]
Goodwill		72.4	73.3
Americas | United States
Goodwill [Roll Forward]
Goodwill		1,006.5	1,006.5
Southern Europe | Italy
Goodwill [Roll Forward]
Goodwill		$ 3.7	$ 3.7

[1] Balances were net of accumulated impairment loss of $694.2 as of both September 30, 2023 and December 31, 2022.