Goodwill - Schedule of Goodwill Balances by Reporting Unit (Details) - USD ($) $ in Millions		Dec. 31, 2023		Dec. 31, 2022		Jan. 01, 2022	Dec. 31, 2021
Goodwill [Line Items]
Goodwill	[2]	$ 1,586.8	[1]	$ 1,628.1	[1]		$ 1,722.2
Jefferson Wells
Goodwill [Line Items]
Goodwill		55.5
Netherlands | Jefferson Wells
Goodwill [Line Items]
Goodwill		0.0		55.1
United Kingdom | Jefferson Wells
Goodwill [Line Items]
Goodwill		105.7		100.2
Canada
Goodwill [Line Items]
Goodwill		42.6		41.6
Americas | United States
Goodwill [Line Items]
Goodwill		1,006.5		1,006.5		$ 1,013.0
Americas | United States | Jefferson Wells
Goodwill [Line Items]
Goodwill		1,085.3		1,085.3
Southern Europe | France
Goodwill [Line Items]
Goodwill		81.7		79.5
Other Reporting Units
Goodwill [Line Items]
Goodwill		$ 271.5		$ 266.4

[1] Balances were net of accumulated impairment loss of $749.3 and $694.2 as of December 31, 2023 and 2022, respectively.

[2] Balances were net of accumulated impairment loss of $694.2 ($177.0 related to Northern Europe, $3.8 related to APME, $235.2 related to Right Management and $278.2 related to Corporate) as of December 31, 2022; and $749.3 ($232.1 related to Northern Europe, $3.8 related to APME, $235.2 related to Right Management and $278.2 related to Corporate) as of December 31, 2023.