Revenue Recognition - Disaggregation of Revenue (Details) - USD ($) $ in Millions	3 Months Ended				6 Months Ended
	Jun. 30, 2025		Jun. 30, 2024		Jun. 30, 2025		Jun. 30, 2024
Disaggregation of Revenue [Line Items]
Revenue	$ 4,519.3		$ 4,520.7	[1]	$ 8,609.6		$ 8,924.0	[2]
Reportable subsegments
Disaggregation of Revenue [Line Items]
Revenue	4,519.3		4,520.7		8,609.6		8,924.0
Intercompany Eliminations
Disaggregation of Revenue [Line Items]
Revenue	(9.7)		(20.4)	[1]	(17.3)		(40.2)	[2]
Americas | Reportable subsegments
Disaggregation of Revenue [Line Items]
Revenue	1,060.0		1,064.4	[1]	2,116.7		2,100.8	[2]
Americas | Services transferred over time
Disaggregation of Revenue [Line Items]
Revenue	1,040.6		1,040.6	[3]	2,078.0		2,051.4	[4]
Americas | Services transferred at a point in time
Disaggregation of Revenue [Line Items]
Revenue	19.4		23.8	[3]	38.7		49.4	[4]
Americas | United States
Disaggregation of Revenue [Line Items]
Revenue			697.0	[3]			1,377.4	[4]
Americas | United States | Reportable subsegments
Disaggregation of Revenue [Line Items]
Revenue	674.1	[5]	697.0	[1],[6]	1,362.9	[7]	1,377.4	[2],[8]
Americas | United States | Services transferred over time
Disaggregation of Revenue [Line Items]
Revenue	660.2		681.2	[3]	1,333.8		1,343.9	[4]
Americas | United States | Services transferred at a point in time
Disaggregation of Revenue [Line Items]
Revenue	13.9		15.8	[3]	29.1		33.5	[4]
Americas | Other Americas
Disaggregation of Revenue [Line Items]
Revenue			367.4	[3]			723.4	[4]
Americas | Other Americas | Reportable subsegments
Disaggregation of Revenue [Line Items]
Revenue	385.9		367.4	[1]	753.8		723.4	[2]
Americas | Other Americas | Services transferred over time
Disaggregation of Revenue [Line Items]
Revenue	380.4		359.4	[3]	744.2		707.5	[4]
Americas | Other Americas | Services transferred at a point in time
Disaggregation of Revenue [Line Items]
Revenue	5.5		8.0	[3]	9.6		15.9	[4]
Americas | Staffing and Interim
Disaggregation of Revenue [Line Items]
Revenue	956.4		966.1	[1]	1,914.7		1,901.1	[2]
Americas | Staffing and Interim | United States
Disaggregation of Revenue [Line Items]
Revenue	599.6		626.8	[1]	1,215.7		1,231.2	[2]
Americas | Staffing and Interim | Other Americas
Disaggregation of Revenue [Line Items]
Revenue	356.8		339.3	[1]	699.0		669.9	[2]
Americas | Outcome-Based Solutions and Consulting
Disaggregation of Revenue [Line Items]
Revenue	19.5		15.3	[1]	36.6		29.4	[2]
Americas | Outcome-Based Solutions and Consulting | United States
Disaggregation of Revenue [Line Items]
Revenue	3.1		2.8	[1]	5.4		5.8	[2]
Americas | Outcome-Based Solutions and Consulting | Other Americas
Disaggregation of Revenue [Line Items]
Revenue	16.4		12.5	[1]	31.2		23.6	[2]
Americas | Permanent Recruitment
Disaggregation of Revenue [Line Items]
Revenue	35.9		38.9	[1]	73.5		81.3	[2]
Americas | Permanent Recruitment | United States
Disaggregation of Revenue [Line Items]
Revenue	26.3		26.6	[1]	55.6		57.2	[2]
Americas | Permanent Recruitment | Other Americas
Disaggregation of Revenue [Line Items]
Revenue	9.6		12.3	[1]	17.9		24.1	[2]
Americas | Other
Disaggregation of Revenue [Line Items]
Revenue	48.2		44.1	[1]	91.9		89.0	[2]
Americas | Other | United States
Disaggregation of Revenue [Line Items]
Revenue	45.1		40.8	[1]	86.2		83.2	[2]
Americas | Other | Other Americas
Disaggregation of Revenue [Line Items]
Revenue	3.1		3.3	[1]	5.7		5.8	[2]
Southern Europe | Reportable subsegments
Disaggregation of Revenue [Line Items]
Revenue	2,149.3		2,098.0	[3]	3,983.3		4,079.3	[2]
Southern Europe | Services transferred over time
Disaggregation of Revenue [Line Items]
Revenue	2,116.0		2,062.8	[3]	3,917.4		4,006.2	[4]
Southern Europe | Services transferred at a point in time
Disaggregation of Revenue [Line Items]
Revenue	33.3		35.2	[3]	65.9		73.1	[4]
Southern Europe | France
Disaggregation of Revenue [Line Items]
Revenue			1,164.1	[3]			2,263.4	[4]
Southern Europe | France | Reportable subsegments
Disaggregation of Revenue [Line Items]
Revenue	1,149.3		1,164.1	[1]	2,115.0		2,263.4	[2]
Southern Europe | France | Services transferred over time
Disaggregation of Revenue [Line Items]
Revenue	1,139.1		1,151.8	[3]	2,094.2		2,237.5	[4]
Southern Europe | France | Services transferred at a point in time
Disaggregation of Revenue [Line Items]
Revenue	10.2		12.3	[3]	20.8		25.9	[4]
Southern Europe | Italy
Disaggregation of Revenue [Line Items]
Revenue			434.9	[3]			839.2	[4]
Southern Europe | Italy | Reportable subsegments
Disaggregation of Revenue [Line Items]
Revenue	475.9		434.9	[1]	873.7		839.2	[2]
Southern Europe | Italy | Services transferred over time
Disaggregation of Revenue [Line Items]
Revenue	463.9		422.8	[3]	850.5		814.4	[4]
Southern Europe | Italy | Services transferred at a point in time
Disaggregation of Revenue [Line Items]
Revenue	12.0		12.1	[3]	23.2		24.8	[4]
Southern Europe | Other Southern Europe
Disaggregation of Revenue [Line Items]
Revenue			499.0	[3]			976.7	[4]
Southern Europe | Other Southern Europe | Reportable subsegments
Disaggregation of Revenue [Line Items]
Revenue	524.1		499.0	[1]	994.6		976.7	[2]
Southern Europe | Other Southern Europe | Services transferred over time
Disaggregation of Revenue [Line Items]
Revenue	513.0		488.2	[3]	972.7		954.3	[4]
Southern Europe | Other Southern Europe | Services transferred at a point in time
Disaggregation of Revenue [Line Items]
Revenue	11.1		10.8	[3]	21.9		22.4	[4]
Southern Europe | Staffing and Interim
Disaggregation of Revenue [Line Items]
Revenue	1,914.2		1,865.5		3,526.0		3,617.0	[2]
Southern Europe | Staffing and Interim | France
Disaggregation of Revenue [Line Items]
Revenue	1,050.5		1,063.6	[1]	1,922.1		2,061.3	[2]
Southern Europe | Staffing and Interim | Italy
Disaggregation of Revenue [Line Items]
Revenue	441.7		401.7	[1]	810.5		777.8	[2]
Southern Europe | Staffing and Interim | Other Southern Europe
Disaggregation of Revenue [Line Items]
Revenue	422.0		400.2	[1]	793.4		777.9	[2]
Southern Europe | Outcome-Based Solutions and Consulting
Disaggregation of Revenue [Line Items]
Revenue	155.7		153.7		306.9		307.6	[2]
Southern Europe | Outcome-Based Solutions and Consulting | France
Disaggregation of Revenue [Line Items]
Revenue	65.6		65.4	[1]	129.6		132.2	[2]
Southern Europe | Outcome-Based Solutions and Consulting | Italy
Disaggregation of Revenue [Line Items]
Revenue	12.9		9.4	[1]	24.0		17.5	[2]
Southern Europe | Outcome-Based Solutions and Consulting | Other Southern Europe
Disaggregation of Revenue [Line Items]
Revenue	77.2		78.9	[1]	153.3		157.9	[2]
Southern Europe | Permanent Recruitment
Disaggregation of Revenue [Line Items]
Revenue	38.7		39.6		75.7		81.8	[2]
Southern Europe | Permanent Recruitment | France
Disaggregation of Revenue [Line Items]
Revenue	11.5		13.7	[1]	22.8		28.5	[2]
Southern Europe | Permanent Recruitment | Italy
Disaggregation of Revenue [Line Items]
Revenue	12.9		13.1	[1]	24.9		26.7	[2]
Southern Europe | Permanent Recruitment | Other Southern Europe
Disaggregation of Revenue [Line Items]
Revenue	14.3		12.8	[1]	28.0		26.6	[2]
Southern Europe | Other
Disaggregation of Revenue [Line Items]
Revenue	40.7				74.7		72.9	[2]
Southern Europe | Other | France
Disaggregation of Revenue [Line Items]
Revenue	21.7		21.4	[1]	40.5		41.4	[2]
Southern Europe | Other | Italy
Disaggregation of Revenue [Line Items]
Revenue	8.4		10.7	[1]	14.3		17.2	[2]
Southern Europe | Other | Other Southern Europe
Disaggregation of Revenue [Line Items]
Revenue	10.6		7.1	[1]	19.9		14.3	[2]
Northern Europe | Reportable subsegments
Disaggregation of Revenue [Line Items]
Revenue	794.4		837.3	[1]	1,525.2	[2]	1,707.6	[2]
Northern Europe | Services transferred over time
Disaggregation of Revenue [Line Items]
Revenue	773.8		812.0	[3]	1,484.1		1,655.5	[4]
Northern Europe | Services transferred at a point in time
Disaggregation of Revenue [Line Items]
Revenue	20.6		25.3	[3]	41.1		52.1	[4]
Northern Europe | Staffing and Interim
Disaggregation of Revenue [Line Items]
Revenue	682.9		714.1	[1]	1,303.9		1,452.2	[2]
Northern Europe | Outcome-Based Solutions and Consulting
Disaggregation of Revenue [Line Items]
Revenue	56.9		64.8	[1]	115.6		137.7	[2]
Northern Europe | Permanent Recruitment
Disaggregation of Revenue [Line Items]
Revenue	27.3		31.8	[1]	54.0		65.6	[2]
Northern Europe | Other
Disaggregation of Revenue [Line Items]
Revenue	27.3		26.6	[1]	51.7	[2]	52.1	[2]
APME | Reportable subsegments
Disaggregation of Revenue [Line Items]
Revenue	525.3		541.4	[1]	1,001.7		1,076.5	[2]
APME | Services transferred over time
Disaggregation of Revenue [Line Items]
Revenue	513.3		528.9	[3]	980.1		1,053.4	[4]
APME | Services transferred at a point in time
Disaggregation of Revenue [Line Items]
Revenue	12.0		12.5	[3]	21.6		23.1	[4]
APME | Staffing and Interim
Disaggregation of Revenue [Line Items]
Revenue	437.5		431.6	[1]	833.5		857.8	[2]
APME | Outcome-Based Solutions and Consulting
Disaggregation of Revenue [Line Items]
Revenue	64.2		84.6	[1]	124.7		170.7	[2]
APME | Permanent Recruitment
Disaggregation of Revenue [Line Items]
Revenue	13.7		14.8	[1]	25.0		27.4	[2]
APME | Other
Disaggregation of Revenue [Line Items]
Revenue	9.9		10.4	[1]	18.5		20.6	[2]
Northern Europe and APME | Reportable subsegments
Disaggregation of Revenue [Line Items]
Revenue	4,529.0		4,541.1	[1]	8,626.9		8,964.2	[2]
Northern Europe and APME | Services transferred over time
Disaggregation of Revenue [Line Items]
Revenue	4,443.7		4,444.3	[3]	8,459.6		8,766.5	[4]
Northern Europe and APME | Services transferred at a point in time
Disaggregation of Revenue [Line Items]
Revenue	85.3		96.8	[3]	167.3		197.7	[4]
Northern Europe and APME | Staffing and Interim
Disaggregation of Revenue [Line Items]
Revenue	3,991.0		3,977.3	[1]	7,578.1		7,828.1	[2]
Northern Europe and APME | Outcome-Based Solutions and Consulting
Disaggregation of Revenue [Line Items]
Revenue	296.3		318.4	[1]	583.8		645.4	[2]
Northern Europe and APME | Permanent Recruitment
Disaggregation of Revenue [Line Items]
Revenue	115.6		125.1	[1]	228.2		256.1	[2]
Northern Europe and APME | Other
Disaggregation of Revenue [Line Items]
Revenue	$ 126.1		$ 120.3	[1]	$ 236.8		$ 234.6	[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 $2.6 for the three months ended June 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 $3.2 for the three months ended June 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 $4.8 for the six months ended June 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 $5.6 for the six months ended June 30, 2024.