Revenue Recognition - Disaggregation of Revenue (Details) - USD ($) $ in Millions		3 Months Ended			9 Months Ended
		Sep. 30, 2024	Sep. 30, 2023		Sep. 30, 2024	Sep. 30, 2023
Disaggregation of Revenue [Line Items]
Revenue	[1]	$ 4,530.2	$ 4,675.6	[2]	$ 13,454.2	$ 14,284.0	[3]
Reportable subsegments
Disaggregation of Revenue [Line Items]
Revenue		1,050.5
Intercompany Eliminations
Disaggregation of Revenue [Line Items]
Revenue		(7.0)	(23.4)	[2]	(47.2)	(64.1)	[3]
United States | Reportable subsegments
Disaggregation of Revenue [Line Items]
Revenue		697.4				2,180.9	[3]
Other Americas | Reportable subsegments
Disaggregation of Revenue [Line Items]
Revenue		353.1				1,159.3	[3]
Americas | Reportable subsegments
Disaggregation of Revenue [Line Items]
Revenue		1,050.5	1,111.3	[2]	3,151.3	3,340.2	[3]
Americas | Services transferred over time
Disaggregation of Revenue [Line Items]
Revenue		1,026.3	1,083.8	[4]	3,077.7	13,995.6	[5]
Americas | Services transferred at a point in time
Disaggregation of Revenue [Line Items]
Revenue		24.2	27.5	[4]	285.4	352.5	[5]
Americas | United States
Disaggregation of Revenue [Line Items]
Revenue		697.4	730.2	[4]	2,074.8	2,180.9	[5]
Americas | United States | Reportable subsegments
Disaggregation of Revenue [Line Items]
Revenue	[6]	697.4	730.2	[2]	2,074.8	2,180.9
Americas | United States | Services transferred over time
Disaggregation of Revenue [Line Items]
Revenue		678.5	710.5	[4]	2,022.4	2,120.4	[5]
Americas | United States | Services transferred at a point in time
Disaggregation of Revenue [Line Items]
Revenue		18.9	19.7	[4]	52.4	60.5	[5]
Americas | Other Americas
Disaggregation of Revenue [Line Items]
Revenue		353.1	381.1	[4]	1,076.5	1,159.3	[5]
Americas | Other Americas | Reportable subsegments
Disaggregation of Revenue [Line Items]
Revenue		353.1	381.1	[2]	1,076.5	1,159.3
Americas | Other Americas | Services transferred over time
Disaggregation of Revenue [Line Items]
Revenue		347.8	373.3	[4]	1,055.3	1,136.5	[5]
Americas | Other Americas | Services transferred at a point in time
Disaggregation of Revenue [Line Items]
Revenue		5.3	7.8	[4]	21.2	22.8	[5]
Americas | Staffing and Interim
Disaggregation of Revenue [Line Items]
Revenue		943.0	1,006.3	[2]	2,844.1	3,023.5	[3]
Americas | Staffing and Interim | United States
Disaggregation of Revenue [Line Items]
Revenue		615.0	651.2	[2]	1,846.2	1,940.6	[3]
Americas | Staffing and Interim | Other Americas
Disaggregation of Revenue [Line Items]
Revenue		328.0	355.1	[2]	997.9	1,082.9	[3]
Americas | Outcome-Based Solutions and Consulting
Disaggregation of Revenue [Line Items]
Revenue		16.3	16.8	[2]	45.7	48.6	[3]
Americas | Outcome-Based Solutions and Consulting | United States
Disaggregation of Revenue [Line Items]
Revenue		2.8	5.3	[2]	8.6	14.5	[3]
Americas | Outcome-Based Solutions and Consulting | Other Americas
Disaggregation of Revenue [Line Items]
Revenue		13.5	11.5	[2]	37.1	34.1	[3]
Americas | Permanent Recruitment
Disaggregation of Revenue [Line Items]
Revenue		43.5	45.7	[2]	124.8	138.9	[3]
Americas | Permanent Recruitment | United States
Disaggregation of Revenue [Line Items]
Revenue		34.0	33.7	[2]	91.2	103.4	[3]
Americas | Permanent Recruitment | Other Americas
Disaggregation of Revenue [Line Items]
Revenue		9.5	12.0	[2]	33.6	35.5	[3]
Americas | Other
Disaggregation of Revenue [Line Items]
Revenue		47.7	42.5	[2]	136.7	129.2	[3]
Americas | Other | United States
Disaggregation of Revenue [Line Items]
Revenue		45.6	40.0	[2]	128.8	122.4	[3]
Americas | Other | Other Americas
Disaggregation of Revenue [Line Items]
Revenue		2.1	2.5	[2]	7.9	6.8	[3]
Southern Europe | Reportable subsegments
Disaggregation of Revenue [Line Items]
Revenue		2,095.6	2,108.7	[2]	6,174.9	6,403.5	[3]
Southern Europe | Services transferred over time
Disaggregation of Revenue [Line Items]
Revenue		2,065.9	2,074.4	[4]	6,072.1	3,256.9	[5]
Southern Europe | Services transferred at a point in time
Disaggregation of Revenue [Line Items]
Revenue		29.7	34.3	[4]	73.6	83.3	[5]
Southern Europe | France
Disaggregation of Revenue [Line Items]
Revenue		1,179.7	1,209.9	[4]	3,483.9	3,657.4	[5]
Southern Europe | France | Reportable subsegments
Disaggregation of Revenue [Line Items]
Revenue		1,179.7	1,209.9	[2]	3,483.9	3,657.4	[3]
Southern Europe | France | Services transferred over time
Disaggregation of Revenue [Line Items]
Revenue		1,169.5	1,198.6	[4]	3,447.7	3,616.2	[5]
Southern Europe | France | Services transferred at a point in time
Disaggregation of Revenue [Line Items]
Revenue		10.2	11.3	[4]	36.2	41.2	[5]
Southern Europe | Italy
Disaggregation of Revenue [Line Items]
Revenue		419.1	413.7	[4]	1,258.3	1,293.7	[5]
Southern Europe | Italy | Reportable subsegments
Disaggregation of Revenue [Line Items]
Revenue		419.1	413.7	[2]	1,258.3	1,293.7	[3]
Southern Europe | Italy | Services transferred over time
Disaggregation of Revenue [Line Items]
Revenue		409.7	402.7	[4]	1,224.1	1,254.4	[5]
Southern Europe | Italy | Services transferred at a point in time
Disaggregation of Revenue [Line Items]
Revenue		9.4	11.0	[4]	34.2	39.3	[5]
Southern Europe | Other Southern Europe
Disaggregation of Revenue [Line Items]
Revenue		496.8	485.1	[4]	1,432.7	1,452.4	[5]
Southern Europe | Other Southern Europe | Reportable subsegments
Disaggregation of Revenue [Line Items]
Revenue		496.8	485.1	[2]	1,432.7	1,452.4	[3]
Southern Europe | Other Southern Europe | Services transferred over time
Disaggregation of Revenue [Line Items]
Revenue		486.7	473.1	[4]	1,400.3	1,414.7	[5]
Southern Europe | Other Southern Europe | Services transferred at a point in time
Disaggregation of Revenue [Line Items]
Revenue		10.1	12.0	[4]	32.4	37.7	[5]
Southern Europe | Staffing and Interim
Disaggregation of Revenue [Line Items]
Revenue		1,873.3	1,893.0	[2]	5,490.3	5,709.0	[3]
Southern Europe | Staffing and Interim | France
Disaggregation of Revenue [Line Items]
Revenue		1,077.0	1,113.8	[2]	3,170.2	3,348.3	[3]
Southern Europe | Staffing and Interim | Italy
Disaggregation of Revenue [Line Items]
Revenue		394.1	388.8	[2]	1,171.9	1,207.1	[3]
Southern Europe | Staffing and Interim | Other Southern Europe
Disaggregation of Revenue [Line Items]
Revenue		402.2	390.4	[2]	1,148.2	1,153.6	[3]
Southern Europe | Outcome-Based Solutions and Consulting
Disaggregation of Revenue [Line Items]
Revenue		153.4	149.4	[2]	461.0	471.3	[3]
Southern Europe | Outcome-Based Solutions and Consulting | France
Disaggregation of Revenue [Line Items]
Revenue		70.4	67.9	[2]	211.4	212.3	[3]
Southern Europe | Outcome-Based Solutions and Consulting | Italy
Disaggregation of Revenue [Line Items]
Revenue		8.5	8.0	[2]	26.0	27.6	[3]
Southern Europe | Outcome-Based Solutions and Consulting | Other Southern Europe
Disaggregation of Revenue [Line Items]
Revenue		74.5	73.5	[2]	223.6	231.4	[3]
Southern Europe | Permanent Recruitment
Disaggregation of Revenue [Line Items]
Revenue		33.8	39.2	[2]	115.6	133.6	[3]
Southern Europe | Permanent Recruitment | France
Disaggregation of Revenue [Line Items]
Revenue		11.3	12.7	[2]	39.9	45.4	[3]
Southern Europe | Permanent Recruitment | Italy
Disaggregation of Revenue [Line Items]
Revenue		10.3	12.0	[2]	37.0	42.3	[3]
Southern Europe | Permanent Recruitment | Other Southern Europe
Disaggregation of Revenue [Line Items]
Revenue		12.2	14.5	[2]	38.7	45.9	[3]
Southern Europe | Other
Disaggregation of Revenue [Line Items]
Revenue		35.1	27.1	[2]	108.0	89.6	[3]
Southern Europe | Other | France
Disaggregation of Revenue [Line Items]
Revenue		21.0	15.5	[2]	62.4	51.4	[3]
Southern Europe | Other | Italy
Disaggregation of Revenue [Line Items]
Revenue		6.2	4.9	[2]	23.4	16.7	[3]
Southern Europe | Other | Other Southern Europe
Disaggregation of Revenue [Line Items]
Revenue		7.9	6.7	[2]	22.2	21.5	[3]
Northern Europe | Reportable subsegments
Disaggregation of Revenue [Line Items]
Revenue		828.3	914.2	[2]	2,535.9	2,834.3	[3]
Northern Europe | Services transferred over time
Disaggregation of Revenue [Line Items]
Revenue		806.3	885.7	[4]	2,461.8	2,740.1	[5]
Northern Europe | Services transferred at a point in time
Disaggregation of Revenue [Line Items]
Revenue		22.0	28.5	[4]	74.1	94.2	[5]
Northern Europe | Staffing and Interim
Disaggregation of Revenue [Line Items]
Revenue		709.4	773.8	[2]	2,161.6	2,389.2	[3]
Northern Europe | Outcome-Based Solutions and Consulting
Disaggregation of Revenue [Line Items]
Revenue		58.3	78.4	[2]	196.0	250.7	[3]
Northern Europe | Permanent Recruitment
Disaggregation of Revenue [Line Items]
Revenue		28.7	36.5	[2]	94.3	119.5	[3]
Northern Europe | Other
Disaggregation of Revenue [Line Items]
Revenue		31.9	25.5	[2]	84.0	74.9	[3]
APME | Reportable subsegments
Disaggregation of Revenue [Line Items]
Revenue		562.8	564.8	[2]	1,639.3	1,770.1	[3]
APME | Services transferred over time
Disaggregation of Revenue [Line Items]
Revenue		551.0	550.3	[4]	1,604.4	1,713.3	[5]
APME | Services transferred at a point in time
Disaggregation of Revenue [Line Items]
Revenue		11.8	14.5	[4]	34.9	56.8	[5]
APME | Staffing and Interim
Disaggregation of Revenue [Line Items]
Revenue		455.7	438.3	[2]	1,313.5	1,346.4	[3]
APME | Outcome-Based Solutions and Consulting
Disaggregation of Revenue [Line Items]
Revenue		82.4	93.7	[2]	253.1	292.1	[3]
APME | Permanent Recruitment
Disaggregation of Revenue [Line Items]
Revenue		13.6	21.4	[2]	41.0	96.9	[3]
APME | Other
Disaggregation of Revenue [Line Items]
Revenue		11.1	11.4	[2]	31.7	34.7	[3]
Northern Europe and APME | Reportable subsegments
Disaggregation of Revenue [Line Items]
Revenue		4,537.2	4,699.0	[2]	13,501.4	14,348.1	[3]
Northern Europe and APME | Services transferred over time
Disaggregation of Revenue [Line Items]
Revenue		4,449.5	4,594.2	[4]	13,216.0	6,285.3	[5]
Northern Europe and APME | Services transferred at a point in time
Disaggregation of Revenue [Line Items]
Revenue		87.7	104.8	[4]	102.8	118.2	[5]
Northern Europe and APME | Staffing and Interim
Disaggregation of Revenue [Line Items]
Revenue		3,981.4	4,111.4	[2]	11,809.5	12,468.1	[3]
Northern Europe and APME | Outcome-Based Solutions and Consulting
Disaggregation of Revenue [Line Items]
Revenue		310.4	338.3	[2]	955.8	1,062.7	[3]
Northern Europe and APME | Permanent Recruitment
Disaggregation of Revenue [Line Items]
Revenue		119.6	142.8	[2]	375.7	488.9	[3]
Northern Europe and APME | Other
Disaggregation of Revenue [Line Items]
Revenue		$ 125.8	$ 106.5	[2]	$ 360.4	$ 328.4	[3]

[1] Our consolidated revenues from services include fees received from our franchise offices of $3.3 and $3.8 for the three months ended September 30, 2024 and 2023, respectively, and $10.6 and $11.0 for the nine months ended September 30, 2024 and 2023, respectively. These fees are primarily based on revenues generated by the franchise offices, which were $282.5 and $243.5 for the three months ended September 30, 2024 and 2023, respectively, and $847.4 and $744.3 for the nine months ended September 30, 2024 and 2023, respectively.

[2] Effective January 1, 2024, our segment reporting was realigned to include our Puerto Rico business within Other Americas. Accordingly, United States is now adjusted to exclude Puerto Rico. All previously reported results have been restated to conform to the current year presentation.

[3] Effective January 1, 2024, our segment reporting was realigned to include our Puerto Rico business within Other Americas. Accordingly, United States is now adjusted to exclude Puerto Rico. All previously reported results have been restated to conform to the current year presentation.

[4] Effective January 1, 2024, our segment reporting was realigned to include our Puerto Rico business within Other Americas. Accordingly, United States is now adjusted to exclude Puerto Rico. All previously reported results have been restated to conform to the current year presentation.

[5] Effective January 1, 2024, our segment reporting was realigned to include our Puerto Rico business within Other Americas. Accordingly, United States is now adjusted to exclude Puerto Rico. All previously reported results have been restated to conform to the current year presentation.

[6] In the United States, revenues from services included fees received from the related franchise offices of $2.5 and $3.1 for the three months ended September 30, 2024 and 2023, respectively, and $8.1 and $8.9 for the nine months ended September 30, 2024 and 2023, respectively. These fees are primarily based on revenues generated by the franchise offices, which were $91.2 and $98.6 for the three months ended September 30, 2024 and 2023, respectively, and $278.4 and $298.7 for the nine months ended September 30, 2024 and 2023, respectively.