Revenue Recognition - Disaggregation of Revenue (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2025		Mar. 31, 2024
Disaggregation of Revenue [Line Items]
Revenue	$ 4,090.3		$ 4,403.3	[1]
Reportable subsegments
Disaggregation of Revenue [Line Items]
Revenue	4,090.3		4,403.3
Intercompany Eliminations
Disaggregation of Revenue [Line Items]
Revenue	(7.6)		(19.8)	[1]
United States | Reportable subsegments
Disaggregation of Revenue [Line Items]
Revenue	688.8		680.4	[1]
Other Americas | Reportable subsegments
Disaggregation of Revenue [Line Items]
Revenue	367.9		356.0	[1]
Americas | Reportable subsegments
Disaggregation of Revenue [Line Items]
Revenue	1,056.7		1,036.4	[1]
Americas | Services transferred over time
Disaggregation of Revenue [Line Items]
Revenue	1,037.4		1,010.8	[2]
Americas | Services transferred at a point in time
Disaggregation of Revenue [Line Items]
Revenue	19.3		25.6	[2]
Americas | United States
Disaggregation of Revenue [Line Items]
Revenue	688.8		680.4	[2]
Americas | United States | Reportable subsegments
Disaggregation of Revenue [Line Items]
Revenue	688.8	[3]	680.4	[4]
Americas | United States | Services transferred over time
Disaggregation of Revenue [Line Items]
Revenue	673.6		662.7	[2]
Americas | United States | Services transferred at a point in time
Disaggregation of Revenue [Line Items]
Revenue	15.2		17.7	[2]
Americas | Other Americas
Disaggregation of Revenue [Line Items]
Revenue	367.9		356.0	[2]
Americas | Other Americas | Reportable subsegments
Disaggregation of Revenue [Line Items]
Revenue	367.9		356.0
Americas | Other Americas | Services transferred over time
Disaggregation of Revenue [Line Items]
Revenue	363.8		348.1	[2]
Americas | Other Americas | Services transferred at a point in time
Disaggregation of Revenue [Line Items]
Revenue	4.1		7.9	[2]
Americas | Staffing and Interim
Disaggregation of Revenue [Line Items]
Revenue	958.3		935.0	[1]
Americas | Staffing and Interim | United States
Disaggregation of Revenue [Line Items]
Revenue	616.1		604.4	[1]
Americas | Staffing and Interim | Other Americas
Disaggregation of Revenue [Line Items]
Revenue	342.2		330.6	[1]
Americas | Outcome-Based Solutions and Consulting
Disaggregation of Revenue [Line Items]
Revenue	17.1		14.1	[1]
Americas | Outcome-Based Solutions and Consulting | United States
Disaggregation of Revenue [Line Items]
Revenue	2.3		3.0	[1]
Americas | Outcome-Based Solutions and Consulting | Other Americas
Disaggregation of Revenue [Line Items]
Revenue	14.8		11.1	[1]
Americas | Permanent Recruitment
Disaggregation of Revenue [Line Items]
Revenue	37.6		42.4	[1]
Americas | Permanent Recruitment | United States
Disaggregation of Revenue [Line Items]
Revenue	29.3		30.6	[1]
Americas | Permanent Recruitment | Other Americas
Disaggregation of Revenue [Line Items]
Revenue	8.3		11.8	[1]
Americas | Other
Disaggregation of Revenue [Line Items]
Revenue	43.7		44.9	[1]
Americas | Other | United States
Disaggregation of Revenue [Line Items]
Revenue	41.1		42.4	[1]
Americas | Other | Other Americas
Disaggregation of Revenue [Line Items]
Revenue	2.6		2.5	[1]
Southern Europe | Reportable subsegments
Disaggregation of Revenue [Line Items]
Revenue	1,834.0		1,981.3	[1]
Southern Europe | Services transferred over time
Disaggregation of Revenue [Line Items]
Revenue	1,801.4		1,943.4	[2]
Southern Europe | Services transferred at a point in time
Disaggregation of Revenue [Line Items]
Revenue	32.6		37.9	[2]
Southern Europe | France
Disaggregation of Revenue [Line Items]
Revenue	965.7		1,099.3	[2]
Southern Europe | France | Reportable subsegments
Disaggregation of Revenue [Line Items]
Revenue	965.7		1,099.3	[1]
Southern Europe | France | Services transferred over time
Disaggregation of Revenue [Line Items]
Revenue	955.1		1,085.7	[2]
Southern Europe | France | Services transferred at a point in time
Disaggregation of Revenue [Line Items]
Revenue	10.6		13.6	[2]
Southern Europe | Italy
Disaggregation of Revenue [Line Items]
Revenue	397.8		404.3	[2]
Southern Europe | Italy | Reportable subsegments
Disaggregation of Revenue [Line Items]
Revenue	397.8		404.3	[1]
Southern Europe | Italy | Services transferred over time
Disaggregation of Revenue [Line Items]
Revenue	386.6		391.6	[2]
Southern Europe | Italy | Services transferred at a point in time
Disaggregation of Revenue [Line Items]
Revenue	11.2		12.7	[2]
Southern Europe | Other Southern Europe
Disaggregation of Revenue [Line Items]
Revenue	470.5		477.7	[2]
Southern Europe | Other Southern Europe | Reportable subsegments
Disaggregation of Revenue [Line Items]
Revenue	470.5		477.7	[1]
Southern Europe | Other Southern Europe | Services transferred over time
Disaggregation of Revenue [Line Items]
Revenue	459.7		466.1	[2]
Southern Europe | Other Southern Europe | Services transferred at a point in time
Disaggregation of Revenue [Line Items]
Revenue	10.8		11.6	[2]
Southern Europe | Staffing and Interim
Disaggregation of Revenue [Line Items]
Revenue	1,611.8		1,751.5	[1]
Southern Europe | Staffing and Interim | France
Disaggregation of Revenue [Line Items]
Revenue	871.6		997.7	[1]
Southern Europe | Staffing and Interim | Italy
Disaggregation of Revenue [Line Items]
Revenue	368.8		376.1	[1]
Southern Europe | Staffing and Interim | Other Southern Europe
Disaggregation of Revenue [Line Items]
Revenue	371.4		377.7	[1]
Southern Europe | Outcome-Based Solutions and Consulting
Disaggregation of Revenue [Line Items]
Revenue	151.2		153.9	[1]
Southern Europe | Outcome-Based Solutions and Consulting | France
Disaggregation of Revenue [Line Items]
Revenue	64.0		66.8	[1]
Southern Europe | Outcome-Based Solutions and Consulting | Italy
Disaggregation of Revenue [Line Items]
Revenue	11.1		8.1	[1]
Southern Europe | Outcome-Based Solutions and Consulting | Other Southern Europe
Disaggregation of Revenue [Line Items]
Revenue	76.1		79.0	[1]
Southern Europe | Permanent Recruitment
Disaggregation of Revenue [Line Items]
Revenue	37.0		42.2	[1]
Southern Europe | Permanent Recruitment | France
Disaggregation of Revenue [Line Items]
Revenue	11.3		14.9	[1]
Southern Europe | Permanent Recruitment | Italy
Disaggregation of Revenue [Line Items]
Revenue	12.0		13.6	[1]
Southern Europe | Permanent Recruitment | Other Southern Europe
Disaggregation of Revenue [Line Items]
Revenue	13.7		13.7	[1]
Southern Europe | Other
Disaggregation of Revenue [Line Items]
Revenue	34.0		33.7	[1]
Southern Europe | Other | France
Disaggregation of Revenue [Line Items]
Revenue	18.8		19.9	[1]
Southern Europe | Other | Italy
Disaggregation of Revenue [Line Items]
Revenue	5.9		6.5	[1]
Southern Europe | Other | Other Southern Europe
Disaggregation of Revenue [Line Items]
Revenue	9.3		7.3	[1]
Northern Europe | Reportable subsegments
Disaggregation of Revenue [Line Items]
Revenue	730.8		870.3	[1]
Northern Europe | Services transferred over time
Disaggregation of Revenue [Line Items]
Revenue	710.3		843.5	[2]
Northern Europe | Services transferred at a point in time
Disaggregation of Revenue [Line Items]
Revenue	20.5		26.8	[2]
Northern Europe | Staffing and Interim
Disaggregation of Revenue [Line Items]
Revenue	621.0		738.1	[1]
Northern Europe | Outcome-Based Solutions and Consulting
Disaggregation of Revenue [Line Items]
Revenue	58.7		72.9	[1]
Northern Europe | Permanent Recruitment
Disaggregation of Revenue [Line Items]
Revenue	26.7		33.8	[1]
Northern Europe | Other
Disaggregation of Revenue [Line Items]
Revenue	24.4		25.5	[1]
APME | Reportable subsegments
Disaggregation of Revenue [Line Items]
Revenue	476.4		535.1	[1]
APME | Services transferred over time
Disaggregation of Revenue [Line Items]
Revenue	466.8		524.5	[2]
APME | Services transferred at a point in time
Disaggregation of Revenue [Line Items]
Revenue	9.6		10.6	[2]
APME | Staffing and Interim
Disaggregation of Revenue [Line Items]
Revenue	396.0		426.2	[1]
APME | Outcome-Based Solutions and Consulting
Disaggregation of Revenue [Line Items]
Revenue	60.5		86.1	[1]
APME | Permanent Recruitment
Disaggregation of Revenue [Line Items]
Revenue	11.3		12.6	[1]
APME | Other
Disaggregation of Revenue [Line Items]
Revenue	8.6		10.2	[1]
Northern Europe and APME | Reportable subsegments
Disaggregation of Revenue [Line Items]
Revenue	4,097.9		4,423.1	[1]
Northern Europe and APME | Services transferred over time
Disaggregation of Revenue [Line Items]
Revenue	4,015.9		4,322.2	[2]
Northern Europe and APME | Services transferred at a point in time
Disaggregation of Revenue [Line Items]
Revenue	82.0		100.9	[2]
Northern Europe and APME | Staffing and Interim
Disaggregation of Revenue [Line Items]
Revenue	3,587.1		3,850.8	[1]
Northern Europe and APME | Outcome-Based Solutions and Consulting
Disaggregation of Revenue [Line Items]
Revenue	287.5		327.0	[1]
Northern Europe and APME | Permanent Recruitment
Disaggregation of Revenue [Line Items]
Revenue	112.6		131.0	[1]
Northern Europe and APME | Other
Disaggregation of Revenue [Line Items]
Revenue	$ 110.7		$ 114.3	[1]

[1] Effective January 1, 2025, our segment reporting was realigned to include our Morocco business within Other Southern Europe. Accordingly, France is now adjusted to exclude Morocco. All previously reported results have been recast to conform to the current year presentation.

[2] Effective January 1, 2025, our segment reporting was realigned to include our Morocco business within Other Southern Europe. Accordingly, France is now adjusted to exclude Morocco. All previously reported results have been recast to conform to the current year presentation.

[3] The United States revenues above represent revenues from our company-owned branches and franchise fees received from our franchise operations, which were $2.2 for the three months ended March 31, 2025.

[4] The United States revenues above represent revenues from our company-owned branches and franchise fees received from our franchise operations, which were $2.4 for the three months ended March 31, 2024.