Goodwill and Other Intangible Assets - Changes in Carrying Value of Goodwill by Reportable Segment (Parenthetical) (Details) - USD ($) $ in Millions		Mar. 31, 2024	Dec. 31, 2023
Goodwill [Roll Forward]
Goodwill	[1]	$ 1,574.5	$ 1,586.8
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		74.0	75.6
Americas | United States
Goodwill [Roll Forward]
Goodwill		1,005.8	1,005.8
Southern Europe | Italy
Goodwill [Roll Forward]
Goodwill		$ 3.7	$ 3.8

[1] Balances were net of accumulated impairment loss of $749.3 as of both March 31, 2024 and December 31, 2023.