Goodwill - Schedule of Goodwill Balances by Reporting Unit (Details) - USD ($) $ in Millions		Dec. 31, 2022		Dec. 31, 2021		Jan. 01, 2021	Dec. 31, 2020
Goodwill [Line Items]
Goodwill	[2]	$ 1,628.1	[1]	$ 1,722.2	[1]		$ 1,225.8
Jefferson Wells
Goodwill [Line Items]
Goodwill		55.5
Netherlands | Jefferson Wells
Goodwill [Line Items]
Goodwill		55.1		74.3
United Kingdom | Jefferson Wells
Goodwill [Line Items]
Goodwill		100.2		112.2
Canada
Goodwill [Line Items]
Goodwill		41.6		44.5
Americas | United States
Goodwill [Line Items]
Goodwill		1,006.5		1,013.0		$ 490.2
Americas | United States | Jefferson Wells
Goodwill [Line Items]
Goodwill		1,085.3		1,091.7
Northern Europe | Netherlands
Goodwill [Line Items]
Goodwill		55.1
Southern Europe | France
Goodwill [Line Items]
Goodwill		79.5		110.7
Other Reporting Units
Goodwill [Line Items]
Goodwill		$ 266.4		$ 288.8

[1] Balances were net of accumulated impairment loss of $694.2 and $644.2 as of December 31, 2022 and 2021, respectively.

[2] Balances were net of accumulated impairment loss of $644.2 ($127.0 related to Northern Europe, $3.8 related to APME, $235.2 related to Right Management and $278.2 related to corporate) as of both January 1, 2021 and December 31, 2021; and $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.