Goodwill and Other Intangible Assets - Changes in Carrying Value of Goodwill by Reportable Segment (Details) $ in Millions	9 Months Ended
	Sep. 30, 2023 USD ($)
Goodwill [Roll Forward]
Balance, December 31, 2022	$ 1,628.1	[1]
Currency impact	8.0
Balance, September 30, 2023	1,620.1	[1]
Reportable segments | Americas
Goodwill [Roll Forward]
Balance, December 31, 2022	1,049.6	[2]
Currency impact	0.2	[2]
Balance, September 30, 2023	1,049.4	[2]
Reportable segments | Southern Europe
Goodwill [Roll Forward]
Balance, December 31, 2022	148.2	[3]
Currency impact	1.6	[3]
Balance, September 30, 2023	146.6	[3]
Reportable segments | Northern Europe
Goodwill [Roll Forward]
Balance, December 31, 2022	234.8
Currency impact	2.2
Balance, September 30, 2023	232.6
Reportable segments | APME
Goodwill [Roll Forward]
Balance, December 31, 2022	69.5
Currency impact	(4.0)
Balance, September 30, 2023	65.5
Corporate
Goodwill [Roll Forward]
Balance, December 31, 2022	126.0	[4]
Currency impact	0.0	[4]
Balance, September 30, 2023	$ 126.0	[4]

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

[2] Balances related to the United States were $1,006.5 as of both December 31, 2022 and September 30, 2023.

[3] Balances related to France were $73.3 and $72.4 as of December 31, 2022 and September 30, 2023, respectively. Balances related to Italy were $3.7 and $3.6 as of December 31, 2022 and September 30, 2023, respectively

[4] The majority of the Corporate balance relates to goodwill attributable to our acquisitions of Right Management ($62.1) and Jefferson Wells ($55.5). Jefferson Wells is part of the United States reporting unit. Right Management is allocated to the reporting units of the countries in which Right Management operates. For purposes of monitoring our total assets by segment, we do not allocate the Corporate balances to the respective reportable segments as this is commensurate with how we operate our business. We do, however, include these balances within the appropriate reporting units for our goodwill impairment testing.