Goodwill and Other Intangible Assets - Changes in Carrying Value of Goodwill by Reportable Segment (Parenthetical) (Details) - USD ($) $ in Millions		Mar. 31, 2025	Dec. 31, 2024
Goodwill [Roll Forward]
Goodwill	[1]	$ 1,577.9	$ 1,563.4
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		74.1	70.9
Americas | United States
Goodwill [Roll Forward]
Goodwill		1,007.2	1,007.2
Southern Europe | Italy
Goodwill [Roll Forward]
Goodwill		$ 3.7	$ 3.5

[1] Balances were net of accumulated impairment loss of $749.3 as of both March 31, 2025 and December 31, 2024.