Revenue Recognition - Disaggregation of Revenue (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2025		Dec. 31, 2024		Dec. 31, 2023
Disaggregation of Revenue [Line Items]
Revenue	$ 17,957.1		$ 17,853.9	[1]	$ 18,914.5
Intercompany Eliminations
Disaggregation of Revenue [Line Items]
Revenue	(31.0)		(54.9)	[1]	(85.9)
Reportable subsegments
Disaggregation of Revenue [Line Items]
Revenue	17,957.1		17,853.9		18,914.5
Americas | Services transferred over time
Disaggregation of Revenue [Line Items]
Revenue	4,270.5		4,127.4		4,308.6
Americas | Services transferred at a point in time
Disaggregation of Revenue [Line Items]
Revenue	78.3		97.5		106.2
Americas | United States | Services transferred over time
Disaggregation of Revenue [Line Items]
Revenue	2,678.0		2,695.4		2,789.8
Americas | United States | Services transferred at a point in time
Disaggregation of Revenue [Line Items]
Revenue	57.4		71.2		76.4
Americas | Other Americas | Services transferred over time
Disaggregation of Revenue [Line Items]
Revenue	1,592.5		1,432.0		1,518.8
Americas | Other Americas | Services transferred at a point in time
Disaggregation of Revenue [Line Items]
Revenue	20.9		26.3		29.8
Americas | Reportable subsegments
Disaggregation of Revenue [Line Items]
Revenue	4,348.8		4,224.9	[1]	4,414.8	[2]
Americas | Reportable subsegments | United States
Disaggregation of Revenue [Line Items]
Revenue	2,735.4	[3]	2,766.6	[1],[4]	2,866.2	[2]
Americas | Reportable subsegments | Other Americas
Disaggregation of Revenue [Line Items]
Revenue	1,613.4		1,458.3	[1]	1,548.6	[2]
Southern Europe | Services transferred over time
Disaggregation of Revenue [Line Items]
Revenue	8,309.8		8,086.5		8,363.4
Southern Europe | Services transferred at a point in time
Disaggregation of Revenue [Line Items]
Revenue	126.5		131.8		151.9
Southern Europe | France | Services transferred over time
Disaggregation of Revenue [Line Items]
Revenue	4,421.6		4,486.7		4,753.3
Southern Europe | France | Services transferred at a point in time
Disaggregation of Revenue [Line Items]
Revenue	37.8		44.8		36.8
Southern Europe | Italy | Services transferred over time
Disaggregation of Revenue [Line Items]
Revenue	1,777.2		1,632.6		1,657.8
Southern Europe | Italy | Services transferred at a point in time
Disaggregation of Revenue [Line Items]
Revenue	44.9		44.4		51.0
Southern Europe | Other Southern Europe | Services transferred over time
Disaggregation of Revenue [Line Items]
Revenue	2,111.0		1,967.2		1,952.3
Southern Europe | Other Southern Europe | Services transferred at a point in time
Disaggregation of Revenue [Line Items]
Revenue	43.8		42.6		64.1
Southern Europe | Reportable subsegments
Disaggregation of Revenue [Line Items]
Revenue	8,436.3		8,218.3	[1],[5]	8,515.3	[6]
Southern Europe | Reportable subsegments | France
Disaggregation of Revenue [Line Items]
Revenue	4,459.4		4,531.5	[1],[5]	4,790.1	[6]
Southern Europe | Reportable subsegments | Italy
Disaggregation of Revenue [Line Items]
Revenue	1,822.1		1,677.0	[1],[5]	1,708.8	[6]
Southern Europe | Reportable subsegments | Other Southern Europe
Disaggregation of Revenue [Line Items]
Revenue	2,154.8		2,009.8	[1],[5]	2,016.4	[6]
Northern Europe | Services transferred over time
Disaggregation of Revenue [Line Items]
Revenue	3,084.6		3,208.9		3,627.5
Northern Europe | Services transferred at a point in time
Disaggregation of Revenue [Line Items]
Revenue	76.5		95.4		120.5
Northern Europe | Reportable subsegments
Disaggregation of Revenue [Line Items]
Revenue	3,161.1		3,304.3	[1]	3,748.0
APME | Services transferred over time
Disaggregation of Revenue [Line Items]
Revenue	2,000.0		2,116.2		2,255.2
APME | Services transferred at a point in time
Disaggregation of Revenue [Line Items]
Revenue	41.9		45.1		67.1
APME | Reportable subsegments
Disaggregation of Revenue [Line Items]
Revenue	2,041.9		2,161.3	[1]	2,322.3
Northern Europe And APME | Services transferred over time
Disaggregation of Revenue [Line Items]
Revenue	17,664.9		17,539.0		18,554.7
Northern Europe And APME | Services transferred at a point in time
Disaggregation of Revenue [Line Items]
Revenue	323.2		369.8		445.7
Northern Europe And APME | Reportable subsegments
Disaggregation of Revenue [Line Items]
Revenue	17,988.1		17,908.8	[1]	19,000.4
Staffing and Interim | Americas
Disaggregation of Revenue [Line Items]
Revenue	3,935.2		3,805.1	[1]	3,995.1
Staffing and Interim | Americas | United States
Disaggregation of Revenue [Line Items]
Revenue	2,438.2		2,454.5	[1]	2,552.5
Staffing and Interim | Americas | Other Americas
Disaggregation of Revenue [Line Items]
Revenue	1,497.0		1,350.6	[1]	1,442.6
Staffing and Interim | Southern Europe
Disaggregation of Revenue [Line Items]
Revenue	7,507.8		7,311.4	[1]	7,592.0
Staffing and Interim | Southern Europe | France
Disaggregation of Revenue [Line Items]
Revenue	4,072.4		4,136.6	[1]	4,393.5
Staffing and Interim | Southern Europe | Italy
Disaggregation of Revenue [Line Items]
Revenue	1,694.9		1,561.5	[1]	1,590.1
Staffing and Interim | Southern Europe | Other Southern Europe
Disaggregation of Revenue [Line Items]
Revenue	1,740.5		1,613.3	[1]	1,608.4
Staffing and Interim | Northern Europe
Disaggregation of Revenue [Line Items]
Revenue	2,731.0		2,814.0	[1]	3,160.2
Staffing and Interim | APME
Disaggregation of Revenue [Line Items]
Revenue	1,704.2		1,746.1	[1]	1,781.8
Staffing and Interim | Northern Europe And APME
Disaggregation of Revenue [Line Items]
Revenue	15,878.2		15,676.6	[1]	16,529.1
Outcome-Based Solutions and Consulting | Americas
Disaggregation of Revenue [Line Items]
Revenue	76.9		65.5	[1]	67.7
Outcome-Based Solutions and Consulting | Americas | United States
Disaggregation of Revenue [Line Items]
Revenue	10.6		11.3	[1]	18.3
Outcome-Based Solutions and Consulting | Americas | Other Americas
Disaggregation of Revenue [Line Items]
Revenue	66.3		54.2	[1]	49.4
Outcome-Based Solutions and Consulting | Southern Europe
Disaggregation of Revenue [Line Items]
Revenue	634.1		614.2	[1]	625.5
Outcome-Based Solutions and Consulting | Southern Europe | France
Disaggregation of Revenue [Line Items]
Revenue	263.4		264.1	[1]	267.7
Outcome-Based Solutions and Consulting | Southern Europe | Italy
Disaggregation of Revenue [Line Items]
Revenue	50.0		36.0	[1]	36.9
Outcome-Based Solutions and Consulting | Southern Europe | Other Southern Europe
Disaggregation of Revenue [Line Items]
Revenue	320.7		314.1	[1]	320.9
Outcome-Based Solutions and Consulting | Northern Europe
Disaggregation of Revenue [Line Items]
Revenue	231.0		257.2	[1]	332.5
Outcome-Based Solutions and Consulting | APME
Disaggregation of Revenue [Line Items]
Revenue	249.0		321.9	[1]	386.3
Outcome-Based Solutions and Consulting | Northern Europe And APME
Disaggregation of Revenue [Line Items]
Revenue	1,191.0		1,258.8	[1]	1,412.0
Permanent Recruitment | Americas
Disaggregation of Revenue [Line Items]
Revenue	147.6		169.1	[1]	179.9
Permanent Recruitment | Americas | United States
Disaggregation of Revenue [Line Items]
Revenue	110.0		126.1	[1]	132.7
Permanent Recruitment | Americas | Other Americas
Disaggregation of Revenue [Line Items]
Revenue	37.6		43.0	[1]	47.2
Permanent Recruitment | Southern Europe
Disaggregation of Revenue [Line Items]
Revenue	145.8		148.2	[1]	172.8
Permanent Recruitment | Southern Europe | France
Disaggregation of Revenue [Line Items]
Revenue	41.3		49.4	[1]	58.9
Permanent Recruitment | Southern Europe | Italy
Disaggregation of Revenue [Line Items]
Revenue	48.2		48.0	[1]	55.0
Permanent Recruitment | Southern Europe | Other Southern Europe
Disaggregation of Revenue [Line Items]
Revenue	56.3		50.8	[1]	58.9
Permanent Recruitment | Northern Europe
Disaggregation of Revenue [Line Items]
Revenue	100.4		121.5	[1]	153.2
Permanent Recruitment | APME
Disaggregation of Revenue [Line Items]
Revenue	48.5		52.8	[1]	109.4
Permanent Recruitment | Northern Europe And APME
Disaggregation of Revenue [Line Items]
Revenue	442.3		491.6	[1]	615.3
Other | Americas
Disaggregation of Revenue [Line Items]
Revenue	189.1		185.2	[1]	172.1
Other | Americas | United States
Disaggregation of Revenue [Line Items]
Revenue	176.6		174.7	[1]	162.7
Other | Americas | Other Americas
Disaggregation of Revenue [Line Items]
Revenue	12.5		10.5	[1]	9.4
Other | Southern Europe
Disaggregation of Revenue [Line Items]
Revenue	148.6		144.5	[1]	125.0
Other | Southern Europe | France
Disaggregation of Revenue [Line Items]
Revenue	82.3		81.4	[1]	70.0
Other | Southern Europe | Italy
Disaggregation of Revenue [Line Items]
Revenue	29.0		31.5	[1]	26.8
Other | Southern Europe | Other Southern Europe
Disaggregation of Revenue [Line Items]
Revenue	37.3		31.6	[1]	28.2
Other | Northern Europe
Disaggregation of Revenue [Line Items]
Revenue	98.7		111.6	[1]	102.1
Other | APME
Disaggregation of Revenue [Line Items]
Revenue	40.2		40.5	[1]	44.8
Other | Northern Europe And APME
Disaggregation of Revenue [Line Items]
Revenue	$ 476.6		$ 481.8	[1]	$ 444.0

[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] The United States revenues above represent revenues from our company-owned branches and franchise fees received from our franchise operations, which were $11.9 for 2023.

[3] The United States revenues above represent revenues from our company-owned branches and franchise fees received from our franchise operations, which were $10.1 for 2025.

[4] The United States revenues above represent revenues from our company-owned branches and franchise fees received from our franchise operations, which were $10.7 for 2024.

[5] 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.

[6] 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.