Revenue Recognition - Disaggregation of Revenue (Details) - USD ($) $ in Millions	3 Months Ended				9 Months Ended
	Sep. 30, 2025		Sep. 30, 2024		Sep. 30, 2025		Sep. 30, 2024
Disaggregation of Revenue [Line Items]
Revenue	$ 4,634.4		$ 4,530.2	[1]	$ 13,244.0		$ 13,454.2	[2]
Reportable subsegments
Disaggregation of Revenue [Line Items]
Revenue	4,634.4		4,530.2		13,244.0		13,454.2
Intercompany Eliminations
Disaggregation of Revenue [Line Items]
Revenue	(7.1)		(7.0)	[1]	(24.4)		(47.2)	[2]
Americas | Reportable subsegments
Disaggregation of Revenue [Line Items]
Revenue	1,098.7		1,050.5	[1]	3,215.4		3,151.3	[2]
Americas | Services transferred over time
Disaggregation of Revenue [Line Items]
Revenue	1,079.5		1,026.3	[3]	3,157.5		3,077.7	[4]
Americas | Services transferred at a point in time
Disaggregation of Revenue [Line Items]
Revenue	19.2		24.2	[3]	57.9		73.6	[4]
Americas | United States
Disaggregation of Revenue [Line Items]
Revenue			697.4	[3]			2,074.8	[4]
Americas | United States | Reportable subsegments
Disaggregation of Revenue [Line Items]
Revenue	690.8	[5]	697.4	[1],[6]	2,053.7	[7]	2,074.8	[2],[8]
Americas | United States | Services transferred over time
Disaggregation of Revenue [Line Items]
Revenue	676.6		678.5	[3]	2,010.4		2,022.4	[4]
Americas | United States | Services transferred at a point in time
Disaggregation of Revenue [Line Items]
Revenue	14.2		18.9	[3]	43.3		52.4	[4]
Americas | Other Americas
Disaggregation of Revenue [Line Items]
Revenue			353.1	[3]			1,076.5	[4]
Americas | Other Americas | Reportable subsegments
Disaggregation of Revenue [Line Items]
Revenue	407.9		353.1	[1]	1,161.7		1,076.5	[2]
Americas | Other Americas | Services transferred over time
Disaggregation of Revenue [Line Items]
Revenue	402.9		347.8	[3]	1,147.1		1,055.3	[4]
Americas | Other Americas | Services transferred at a point in time
Disaggregation of Revenue [Line Items]
Revenue	5.0		5.3	[3]	14.6		21.2	[4]
Americas | Staffing and Interim
Disaggregation of Revenue [Line Items]
Revenue	996.1		943.0	[1]	2,910.8		2,844.1	[2]
Americas | Staffing and Interim | United States
Disaggregation of Revenue [Line Items]
Revenue	617.4		615.0	[1]	1,833.1		1,846.2	[2]
Americas | Staffing and Interim | Other Americas
Disaggregation of Revenue [Line Items]
Revenue	378.7		328.0	[1]	1,077.7		997.9	[2]
Americas | Outcome-Based Solutions and Consulting
Disaggregation of Revenue [Line Items]
Revenue	19.6		16.3	[1]	56.2		45.7	[2]
Americas | Outcome-Based Solutions and Consulting | United States
Disaggregation of Revenue [Line Items]
Revenue	2.8		2.8	[1]	8.2		8.6	[2]
Americas | Outcome-Based Solutions and Consulting | Other Americas
Disaggregation of Revenue [Line Items]
Revenue	16.8		13.5	[1]	48.0		37.1	[2]
Americas | Permanent Recruitment
Disaggregation of Revenue [Line Items]
Revenue	36.6		43.5	[1]	110.1		124.8	[2]
Americas | Permanent Recruitment | United States
Disaggregation of Revenue [Line Items]
Revenue	27.4		34.0	[1]	83.0		91.2	[2]
Americas | Permanent Recruitment | Other Americas
Disaggregation of Revenue [Line Items]
Revenue	9.2		9.5	[1]	27.1		33.6	[2]
Americas | Other
Disaggregation of Revenue [Line Items]
Revenue	46.4		47.7	[1]	138.3		136.7	[2]
Americas | Other | United States
Disaggregation of Revenue [Line Items]
Revenue	43.2		45.6	[1]	129.4		128.8	[2]
Americas | Other | Other Americas
Disaggregation of Revenue [Line Items]
Revenue	3.2		2.1	[1]	8.9		7.9	[2]
Southern Europe | Reportable subsegments
Disaggregation of Revenue [Line Items]
Revenue	2,205.5		2,095.6	[1]	6,188.8		6,174.9	[2]
Southern Europe | Services transferred over time
Disaggregation of Revenue [Line Items]
Revenue	2,175.4		2,065.9	[3]	6,092.8		6,072.1	[4]
Southern Europe | Services transferred at a point in time
Disaggregation of Revenue [Line Items]
Revenue	30.1		29.7	[3]	96.0		102.8	[4]
Southern Europe | France
Disaggregation of Revenue [Line Items]
Revenue			1,156.8	[3]			3,420.2	[4]
Southern Europe | France | Reportable subsegments
Disaggregation of Revenue [Line Items]
Revenue	1,173.5		1,156.8	[1]	3,288.5		3,420.2	[2]
Southern Europe | France | Services transferred over time
Disaggregation of Revenue [Line Items]
Revenue	1,164.3		1,146.7	[3]	3,258.5		3,384.2	[4]
Southern Europe | France | Services transferred at a point in time
Disaggregation of Revenue [Line Items]
Revenue	9.2		10.1	[3]	30.0		36.0	[4]
Southern Europe | Italy
Disaggregation of Revenue [Line Items]
Revenue			419.1	[3]			1,258.3	[4]
Southern Europe | Italy | Reportable subsegments
Disaggregation of Revenue [Line Items]
Revenue	462.5		419.1	[1]	1,336.2		1,258.3	[2]
Southern Europe | Italy | Services transferred over time
Disaggregation of Revenue [Line Items]
Revenue	452.2		409.7	[3]	1,302.7		1,224.1	[4]
Southern Europe | Italy | Services transferred at a point in time
Disaggregation of Revenue [Line Items]
Revenue	10.3		9.4	[3]	33.5		34.2	[4]
Southern Europe | Other Southern Europe
Disaggregation of Revenue [Line Items]
Revenue			519.7	[3]			1,496.4	[4]
Southern Europe | Other Southern Europe | Reportable subsegments
Disaggregation of Revenue [Line Items]
Revenue	569.5		519.7	[1]	1,564.1		1,496.4	[2]
Southern Europe | Other Southern Europe | Services transferred over time
Disaggregation of Revenue [Line Items]
Revenue	558.9		509.5	[3]	1,531.6		1,463.8	[4]
Southern Europe | Other Southern Europe | Services transferred at a point in time
Disaggregation of Revenue [Line Items]
Revenue	10.6		10.2	[3]	32.5		32.6	[4]
Southern Europe | Staffing and Interim
Disaggregation of Revenue [Line Items]
Revenue	1,976.1		1,873.3	[1]	5,502.1		5,490.3	[2]
Southern Europe | Staffing and Interim | France
Disaggregation of Revenue [Line Items]
Revenue	1,077.6		1,058.7	[1]	2,999.7		3,120.0	[2]
Southern Europe | Staffing and Interim | Italy
Disaggregation of Revenue [Line Items]
Revenue	434.1		394.1	[1]	1,244.6		1,171.9	[2]
Southern Europe | Staffing and Interim | Other Southern Europe
Disaggregation of Revenue [Line Items]
Revenue	464.4		420.5	[1]	1,257.8		1,198.4	[2]
Southern Europe | Outcome-Based Solutions and Consulting
Disaggregation of Revenue [Line Items]
Revenue	158.7		153.4	[1]	465.6		461.0	[2]
Southern Europe | Outcome-Based Solutions and Consulting | France
Disaggregation of Revenue [Line Items]
Revenue	65.8		66.0	[1]	195.4		198.2	[2]
Southern Europe | Outcome-Based Solutions and Consulting | Italy
Disaggregation of Revenue [Line Items]
Revenue	11.2		8.5	[1]	35.2		26.0	[2]
Southern Europe | Outcome-Based Solutions and Consulting | Other Southern Europe
Disaggregation of Revenue [Line Items]
Revenue	81.7		78.9	[1]	235.0		236.8	[2]
Southern Europe | Permanent Recruitment
Disaggregation of Revenue [Line Items]
Revenue	34.9		33.8	[1]	110.6		115.6	[2]
Southern Europe | Permanent Recruitment | France
Disaggregation of Revenue [Line Items]
Revenue	10.1		11.2	[1]	32.9		39.7	[2]
Southern Europe | Permanent Recruitment | Italy
Disaggregation of Revenue [Line Items]
Revenue	11.0		10.3	[1]	35.9		37.0	[2]
Southern Europe | Permanent Recruitment | Other Southern Europe
Disaggregation of Revenue [Line Items]
Revenue	13.8		12.3	[1]	41.8		38.9	[2]
Southern Europe | Other
Disaggregation of Revenue [Line Items]
Revenue	35.8				110.5		108.0	[2]
Southern Europe | Other | France
Disaggregation of Revenue [Line Items]
Revenue	20.0		20.9	[1]	60.5		62.3	[2]
Southern Europe | Other | Italy
Disaggregation of Revenue [Line Items]
Revenue	6.2		6.2	[1]	20.5		23.4	[2]
Southern Europe | Other | Other Southern Europe
Disaggregation of Revenue [Line Items]
Revenue	9.6		8.0	[1]	29.5		22.3	[2]
Northern Europe | Reportable subsegments
Disaggregation of Revenue [Line Items]
Revenue	816.8		828.3	[1]	2,342.0	[2]	2,535.9	[2]
Northern Europe | Services transferred over time
Disaggregation of Revenue [Line Items]
Revenue	799.2		806.3	[3]	2,283.3		2,461.8	[4]
Northern Europe | Services transferred at a point in time
Disaggregation of Revenue [Line Items]
Revenue	17.6		22.0	[3]	58.7		74.1	[4]
Northern Europe | Staffing and Interim
Disaggregation of Revenue [Line Items]
Revenue	712.1		709.4	[1]	2,016.0		2,161.6	[2]
Northern Europe | Outcome-Based Solutions and Consulting
Disaggregation of Revenue [Line Items]
Revenue	56.7		58.3	[1]	172.3		196.0	[2]
Northern Europe | Permanent Recruitment
Disaggregation of Revenue [Line Items]
Revenue	23.5		28.7	[1]	77.5		94.3	[2]
Northern Europe | Other
Disaggregation of Revenue [Line Items]
Revenue	24.5		31.9	[1]	76.2	[2]	84.0	[2]
APME | Reportable subsegments
Disaggregation of Revenue [Line Items]
Revenue	520.5		562.8	[1]	1,522.2		1,639.3	[2]
APME | Services transferred over time
Disaggregation of Revenue [Line Items]
Revenue	509.4		551.0	[3]	1,489.5		1,604.4	[4]
APME | Services transferred at a point in time
Disaggregation of Revenue [Line Items]
Revenue	11.1		11.8	[3]	32.7		34.9	[4]
APME | Staffing and Interim
Disaggregation of Revenue [Line Items]
Revenue	433.9		455.7	[1]	1,267.4		1,313.5	[2]
APME | Outcome-Based Solutions and Consulting
Disaggregation of Revenue [Line Items]
Revenue	62.9		82.4	[1]	187.6		253.1	[2]
APME | Permanent Recruitment
Disaggregation of Revenue [Line Items]
Revenue	12.8		13.6	[1]	37.8		41.0	[2]
APME | Other
Disaggregation of Revenue [Line Items]
Revenue	10.9		11.1	[1]	29.4		31.7	[2]
Northern Europe and APME | Reportable subsegments
Disaggregation of Revenue [Line Items]
Revenue	4,641.5		4,537.2	[1]	13,268.4		13,501.4	[2]
Northern Europe and APME | Services transferred over time
Disaggregation of Revenue [Line Items]
Revenue	4,563.5		4,449.5	[3]	13,023.1		13,216.0	[4]
Northern Europe and APME | Services transferred at a point in time
Disaggregation of Revenue [Line Items]
Revenue	78.0		87.7	[3]	245.3		285.4	[4]
Northern Europe and APME | Staffing and Interim
Disaggregation of Revenue [Line Items]
Revenue	4,118.2		3,981.4	[1]	11,696.3		11,809.5	[2]
Northern Europe and APME | Outcome-Based Solutions and Consulting
Disaggregation of Revenue [Line Items]
Revenue	297.9		310.4	[1]	881.7		955.8	[2]
Northern Europe and APME | Permanent Recruitment
Disaggregation of Revenue [Line Items]
Revenue	107.8		119.6	[1]	336.0		375.7	[2]
Northern Europe and APME | Other
Disaggregation of Revenue [Line Items]
Revenue	$ 117.6		$ 125.8	[1]	$ 354.4		$ 360.4	[2]

[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] 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.

[4] 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.

[5] The United States revenues above represent revenues from our company-owned branches and franchise fees received from our franchise operations, which were $2.7 for the three months ended September 30, 2025.

[6] The United States revenues above represent revenues from our company-owned branches and franchise fees received from our franchise operations, which were $2.5 for the three months ended September 30, 2024.

[7] The United States revenues above represent revenues from our company-owned branches and franchise fees received from our franchise operations, which were $7.5 for the nine months ended September 30, 2025.

[8] The United States revenues above represent revenues from our company-owned branches and franchise fees received from our franchise operations, which were $8.1 for the nine months ended September 30, 2024.