Goodwill - Changes in Carrying Value of Goodwill by Reportable Segment (Parenthetical) (Details) - USD ($) $ in Millions		12 Months Ended
		Dec. 31, 2025		Dec. 31, 2024		Dec. 31, 2023
Goodwill, Impaired, Accumulated Impairment Loss [Abstract]
Goodwill		$ 1,544.6	[1],[2]	$ 1,563.4	[1],[2]	$ 1,586.8
Goodwill, accumulated impairment loss		807.4		749.3		749.3
Impairment Charge		88.7	[3]	0.0		55.1
Corporate
Goodwill, Impaired, Accumulated Impairment Loss [Abstract]
Goodwill	[4]	125.5	[1]	125.5	[1]	126.0
Goodwill, accumulated impairment loss		278.2		278.2		278.2
Jefferson Wells
Goodwill, Impaired, Accumulated Impairment Loss [Abstract]
Goodwill		(55.5)		(55.5)
Right Management
Goodwill, Impaired, Accumulated Impairment Loss [Abstract]
Goodwill		(62.1)		(62.1)
Goodwill, accumulated impairment loss		235.2		235.2		235.2
Americas | Reportable segments
Goodwill, Impaired, Accumulated Impairment Loss [Abstract]
Goodwill	[5]	1,050.4	[1]	1,048.2	[1]	1,050.4
Americas | United States
Goodwill, Impaired, Accumulated Impairment Loss [Abstract]
Goodwill		1,007.2		1,007.2		1,005.8
Southern Europe | Reportable segments
Goodwill, Impaired, Accumulated Impairment Loss [Abstract]
Goodwill	[6]	139.9	[1]	145.3	[1]	154.7
Goodwill, accumulated impairment loss		24.7
Southern Europe | France
Goodwill, Impaired, Accumulated Impairment Loss [Abstract]
Goodwill		80.5		70.9		75.6
Southern Europe | Italy
Goodwill, Impaired, Accumulated Impairment Loss [Abstract]
Goodwill		4.0		3.5		3.8
Northern Europe | Reportable segments
Goodwill, Impaired, Accumulated Impairment Loss [Abstract]
Goodwill		164.7	[1]	181.4	[1]	188.0
Goodwill, accumulated impairment loss		265.5		232.1		232.1
APME | Reportable segments
Goodwill, Impaired, Accumulated Impairment Loss [Abstract]
Goodwill		64.1	[1]	63.0	[1]	67.7
Goodwill, accumulated impairment loss		$ 3.8		$ 3.8		$ 3.8

[1] Balances were net of accumulated impairment loss of $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 both January 1, 2024 and December 31, 2024; and $807.4 ($24.7 related to Southern Europe, $265.5 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, 2025.

[2] Balances were net of accumulated impairment loss of $807.4 and $749.3 as of December 31, 2025 and 2024, respectively.

[3] Impairment charges for the year ended December 31, 2025 consist of a goodwill impairment related to our investments in Switzerland and the United Kingdom and an impairment of an indefinite-lived intangible asset in our Switzerland business.

[4] The majority of the Corporate balance as of January 1, 2024, December 31, 2024 and 2025 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 balance 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.

[5] Balances related to United States were $1,005.8, $1,007.2 and $1,007.2 as of January 1, 2024, December 31, 2024 and December 31, 2025, respectively.

[6] Balances related to France were $75.6, $70.9 and $80.5 as of January 1, 2024, December 31, 2024 and December 31, 2025, respectively. Balances related to Italy were $3.8, $3.5 and $4.0 as of January 1, 2024, December 31, 2024 and December 31, 2025, respectively.