Revenue Recognition - Disaggregation of Revenue (Details) - USD ($) $ in Millions		3 Months Ended			6 Months Ended
		Jun. 30, 2024	Jun. 30, 2023		Jun. 30, 2024	Jun. 30, 2023
Disaggregation of Revenue [Line Items]
Revenue	[1]	$ 4,520.7	$ 4,856.1	[2]	$ 8,924.0	$ 9,608.4	[3]
Intercompany Eliminations
Disaggregation of Revenue [Line Items]
Revenue		(20.4)	(21.4)	[2]	(40.2)	(40.7)	[3]
Americas | Reportable subsegments
Disaggregation of Revenue [Line Items]
Revenue		1,064.4	1,098.7	[2]	2,100.8	2,228.9	[3]
Americas | Services transferred over time
Disaggregation of Revenue [Line Items]
Revenue		1,040.6	1,071.8	[4]	2,051.4	2,173.1	[5]
Americas | Services transferred at a point in time
Disaggregation of Revenue [Line Items]
Revenue		23.8	26.9	[4]	49.4	55.8	[5]
Americas | United States
Disaggregation of Revenue [Line Items]
Revenue		697.0	709.1	[4]	1,377.4	1,450.7	[5]
Americas | United States | Reportable subsegments
Disaggregation of Revenue [Line Items]
Revenue	[6]	697.0	709.1	[2]	1,377.4	1,450.7	[3]
Americas | United States | Services transferred over time
Disaggregation of Revenue [Line Items]
Revenue		681.2	689.8	[4]	1,343.9	1,409.9	[5]
Americas | United States | Services transferred at a point in time
Disaggregation of Revenue [Line Items]
Revenue		15.8	19.3	[4]	33.5	40.8	[5]
Americas | Other Americas
Disaggregation of Revenue [Line Items]
Revenue		367.4	389.6	[4]	723.4	778.2	[5]
Americas | Other Americas | Reportable subsegments
Disaggregation of Revenue [Line Items]
Revenue		367.4	389.6	[2]	723.4	778.2	[3]
Americas | Other Americas | Services transferred over time
Disaggregation of Revenue [Line Items]
Revenue		359.4	382.0	[4]	707.5	763.2	[5]
Americas | Other Americas | Services transferred at a point in time
Disaggregation of Revenue [Line Items]
Revenue		8.0	7.6	[4]	15.9	15.0	[5]
Americas | Staffing and Interim
Disaggregation of Revenue [Line Items]
Revenue		966.1	994.5	[2]	1,901.1	2,017.2	[3]
Americas | Staffing and Interim | United States
Disaggregation of Revenue [Line Items]
Revenue		626.8	630.7	[2]	1,231.2	1,289.5	[3]
Americas | Staffing and Interim | Other Americas
Disaggregation of Revenue [Line Items]
Revenue		339.3	363.8	[2]	669.9	727.7	[3]
Americas | Outcome-Based Solutions and Consulting
Disaggregation of Revenue [Line Items]
Revenue		15.3	16.5	[2]	29.4	31.8	[3]
Americas | Outcome-Based Solutions and Consulting | United States
Disaggregation of Revenue [Line Items]
Revenue		2.8	5.0	[2]	5.8	9.2	[3]
Americas | Outcome-Based Solutions and Consulting | Other Americas
Disaggregation of Revenue [Line Items]
Revenue		12.5	11.5	[2]	23.6	22.6	[3]
Americas | Permanent Recruitment
Disaggregation of Revenue [Line Items]
Revenue		38.9	43.7	[2]	81.3	93.2	[3]
Americas | Permanent Recruitment | United States
Disaggregation of Revenue [Line Items]
Revenue		26.6	32.0	[2]	57.2	69.7	[3]
Americas | Permanent Recruitment | Other Americas
Disaggregation of Revenue [Line Items]
Revenue		12.3	11.7	[2]	24.1	23.5	[3]
Americas | Other
Disaggregation of Revenue [Line Items]
Revenue		44.1	44.0	[2]	89.0	86.7	[3]
Americas | Other | United States
Disaggregation of Revenue [Line Items]
Revenue		40.8	41.4	[2]	83.2	82.3	[3]
Americas | Other | Other Americas
Disaggregation of Revenue [Line Items]
Revenue		3.3	2.6	[2]	5.8	4.4	[3]
Southern Europe | Reportable subsegments
Disaggregation of Revenue [Line Items]
Revenue		2,098.0	2,226.9	[2]	4,079.3	4,294.8	[3]
Southern Europe | Services transferred over time
Disaggregation of Revenue [Line Items]
Revenue		2,062.8	2,185.3	[4]	4,006.2	4,210.9	[5]
Southern Europe | Services transferred at a point in time
Disaggregation of Revenue [Line Items]
Revenue		35.2	41.6	[4]	73.1	83.9	[5]
Southern Europe | France
Disaggregation of Revenue [Line Items]
Revenue		1,184.9	1,278.2	[4]	2,304.2	2,447.5	[5]
Southern Europe | France | Reportable subsegments
Disaggregation of Revenue [Line Items]
Revenue		1,184.9	1,278.2	[2]	2,304.2	2,447.5	[3]
Southern Europe | France | Services transferred over time
Disaggregation of Revenue [Line Items]
Revenue		1,172.5	1,263.5	[4]	2,278.2	2,417.6	[5]
Southern Europe | France | Services transferred at a point in time
Disaggregation of Revenue [Line Items]
Revenue		12.4	14.7	[4]	26.0	29.9	[5]
Southern Europe | Italy
Disaggregation of Revenue [Line Items]
Revenue		434.9	457.8	[4]	839.2	880.0	[5]
Southern Europe | Italy | Reportable subsegments
Disaggregation of Revenue [Line Items]
Revenue		434.9	457.8	[2]	839.2	880.0	[3]
Southern Europe | Italy | Services transferred over time
Disaggregation of Revenue [Line Items]
Revenue		422.8	443.5	[4]	814.4	851.7	[5]
Southern Europe | Italy | Services transferred at a point in time
Disaggregation of Revenue [Line Items]
Revenue		12.1	14.3	[4]	24.8	28.3	[5]
Southern Europe | Other Southern Europe
Disaggregation of Revenue [Line Items]
Revenue		478.2	490.9	[4]	935.9	967.3	[5]
Southern Europe | Other Southern Europe | Reportable subsegments
Disaggregation of Revenue [Line Items]
Revenue		478.2	490.9	[2]	935.9	967.3	[3]
Southern Europe | Other Southern Europe | Services transferred over time
Disaggregation of Revenue [Line Items]
Revenue		467.5	478.3	[4]	913.6	941.6	[5]
Southern Europe | Other Southern Europe | Services transferred at a point in time
Disaggregation of Revenue [Line Items]
Revenue		10.7	12.6	[4]	22.3	25.7	[5]
Southern Europe | Staffing and Interim
Disaggregation of Revenue [Line Items]
Revenue		1,865.5	1,989.0	[2]	3,617.0	3,816.0	[3]
Southern Europe | Staffing and Interim | France
Disaggregation of Revenue [Line Items]
Revenue		1,079.9	1,172.8	[2]	2,093.2	2,234.5	[3]
Southern Europe | Staffing and Interim | Italy
Disaggregation of Revenue [Line Items]
Revenue		401.7	425.6	[2]	777.8	818.3	[3]
Southern Europe | Staffing and Interim | Other Southern Europe
Disaggregation of Revenue [Line Items]
Revenue		383.9	390.6	[2]	746.0	763.2	[3]
Southern Europe | Outcome-Based Solutions and Consulting
Disaggregation of Revenue [Line Items]
Revenue		153.7	158.7	[2]	307.6	321.9	[3]
Southern Europe | Outcome-Based Solutions and Consulting | France
Disaggregation of Revenue [Line Items]
Revenue		69.9	71.2	[2]	141.0	144.4	[3]
Southern Europe | Outcome-Based Solutions and Consulting | Italy
Disaggregation of Revenue [Line Items]
Revenue		9.4	10.2	[2]	17.5	19.6	[3]
Southern Europe | Outcome-Based Solutions and Consulting | Other Southern Europe
Disaggregation of Revenue [Line Items]
Revenue		74.4	77.3	[2]	149.1	157.9	[3]
Southern Europe | Permanent Recruitment
Disaggregation of Revenue [Line Items]
Revenue		39.6	47.0	[2]	81.8	94.4	[3]
Southern Europe | Permanent Recruitment | France
Disaggregation of Revenue [Line Items]
Revenue		13.7	16.2	[2]	28.6	32.7	[3]
Southern Europe | Permanent Recruitment | Italy
Disaggregation of Revenue [Line Items]
Revenue		13.1	15.3	[2]	26.7	30.3	[3]
Southern Europe | Permanent Recruitment | Other Southern Europe
Disaggregation of Revenue [Line Items]
Revenue		12.8	15.5	[2]	26.5	31.4	[3]
Southern Europe | Other
Disaggregation of Revenue [Line Items]
Revenue		39.2	32.2	[2]	72.9	62.5	[3]
Southern Europe | Other | France
Disaggregation of Revenue [Line Items]
Revenue		21.4	18.0	[2]	41.4	35.9	[3]
Southern Europe | Other | Italy
Disaggregation of Revenue [Line Items]
Revenue		10.7	6.7	[2]	17.2	11.8	[3]
Southern Europe | Other | Other Southern Europe
Disaggregation of Revenue [Line Items]
Revenue		7.1	7.5	[2]	14.3	14.8	[3]
Northern Europe | Reportable subsegments
Disaggregation of Revenue [Line Items]
Revenue		837.3	952.5	[2]	1,707.6	1,920.1	[3]
Northern Europe | Services transferred over time
Disaggregation of Revenue [Line Items]
Revenue		812.0	921.3	[4]	1,655.5	1,854.4	[5]
Northern Europe | Services transferred at a point in time
Disaggregation of Revenue [Line Items]
Revenue		25.3	31.2	[4]	52.1	65.7	[5]
Northern Europe | Staffing and Interim
Disaggregation of Revenue [Line Items]
Revenue		714.1	804.8	[2]	1,452.2	1,615.4	[3]
Northern Europe | Outcome-Based Solutions and Consulting
Disaggregation of Revenue [Line Items]
Revenue		64.8	82.9	[2]	137.7	172.3	[3]
Northern Europe | Permanent Recruitment
Disaggregation of Revenue [Line Items]
Revenue		31.8	39.6	[2]	65.6	83.0	[3]
Northern Europe | Other
Disaggregation of Revenue [Line Items]
Revenue		26.6	25.2	[2]	52.1	49.4	[3]
APME | Reportable subsegments
Disaggregation of Revenue [Line Items]
Revenue		541.4	599.4	[2]	1,076.5	1,205.3	[3]
APME | Services transferred over time
Disaggregation of Revenue [Line Items]
Revenue		528.9	578.4	[4]	1,053.4	1,163.0	[5]
APME | Services transferred at a point in time
Disaggregation of Revenue [Line Items]
Revenue		12.5	21.0	[4]	23.1	42.3	[5]
APME | Staffing and Interim
Disaggregation of Revenue [Line Items]
Revenue		431.6	453.2	[2]	857.8	908.1	[3]
APME | Outcome-Based Solutions and Consulting
Disaggregation of Revenue [Line Items]
Revenue		84.6	97.5	[2]	170.7	198.4	[3]
APME | Permanent Recruitment
Disaggregation of Revenue [Line Items]
Revenue		14.8	36.5	[2]	27.4	75.5	[3]
APME | Other
Disaggregation of Revenue [Line Items]
Revenue		10.4	12.2	[2]	20.6	23.3	[3]
Northern Europe and APME | Reportable subsegments
Disaggregation of Revenue [Line Items]
Revenue		4,541.1	4,877.5	[2]	8,964.2	9,649.1	[3]
Northern Europe and APME | Services transferred over time
Disaggregation of Revenue [Line Items]
Revenue		4,444.3	4,756.8	[4]	8,766.5	9,401.4	[5]
Northern Europe and APME | Services transferred at a point in time
Disaggregation of Revenue [Line Items]
Revenue		96.8	120.7	[4]	197.7	247.7	[5]
Northern Europe and APME | Staffing and Interim
Disaggregation of Revenue [Line Items]
Revenue		3,977.3	4,241.5	[2]	7,828.1	8,356.7	[3]
Northern Europe and APME | Outcome-Based Solutions and Consulting
Disaggregation of Revenue [Line Items]
Revenue		318.4	355.6	[2]	645.4	724.4	[3]
Northern Europe and APME | Permanent Recruitment
Disaggregation of Revenue [Line Items]
Revenue		125.1	166.8	[2]	256.1	346.1	[3]
Northern Europe and APME | Other
Disaggregation of Revenue [Line Items]
Revenue		$ 120.3	$ 113.6	[2]	$ 234.6	$ 221.9	[3]

[1] Our consolidated revenues from services include fees received from our franchise offices of $4.0 and $3.3 for the three months ended June 30, 2024 and 2023, respectively, and $7.3 and $7.2 for the six months ended June 30, 2024 and 2023, respectively. These fees are primarily based on revenues generated by the franchise offices, which were $287.7 and $250.6 for the three months ended June 30, 2024 and 2023, respectively, and $564.9 and $500.8 for the six months ended June 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 $3.2 and $2.6 for the three months ended June 30, 2024 and 2023, respectively, and $5.6 and $5.8 for the six months ended June 30, 2024 and 2023, respectively. These fees are primarily based on revenues generated by the franchise offices, which were $99.8 and $100.8 for the three months ended June 30, 2024 and 2023, respectively, and $187.2 and $200.1 for the six months ended June 30, 2024 and 2023, respectively.