Revenue Recognition - Disaggregation of Revenue (Details) - USD ($) $ in Millions		3 Months Ended		6 Months Ended		12 Months Ended
		Jun. 30, 2023	Jun. 30, 2022	Jun. 30, 2023	Jun. 30, 2022	Dec. 31, 2022
Disaggregation of Revenue [Line Items]
Revenue	[1]	$ 4,856.1	$ 5,074.1	$ 9,608.4	$ 10,217.4
Intercompany Eliminations
Disaggregation of Revenue [Line Items]
Revenue		(21.4)	(20.8)	(40.7)	(35.3)
Staffing and Interim
Disaggregation of Revenue [Line Items]
Revenue				65.2
Outcome-Based Solutions and Consulting | United States
Disaggregation of Revenue [Line Items]
Revenue				113.2		$ 60.4
Americas
Disaggregation of Revenue [Line Items]
Revenue		1,098.7	1,262.7	2,228.9	2,513.9
Americas | Reportable Subsegments [Member]
Disaggregation of Revenue [Line Items]
Revenue		1,098.7	1,262.7	2,228.9	2,513.9
Americas | Services transferred over time
Disaggregation of Revenue [Line Items]
Revenue		1,071.8	1,221.7	2,173.1	2,435.5
Americas | Services transferred at a point in time
Disaggregation of Revenue [Line Items]
Revenue		26.9	41.0	55.8	78.4
Americas | United States
Disaggregation of Revenue [Line Items]
Revenue		736.7	903.9	1,506.7	1,793.3
Americas | United States | Reportable Subsegments [Member]
Disaggregation of Revenue [Line Items]
Revenue	[2]	736.7	903.9	1,506.7	1,793.3
Americas | United States | Services transferred over time
Disaggregation of Revenue [Line Items]
Revenue		717.3	871.0	1,465.7	1,729.8
Americas | United States | Services transferred at a point in time
Disaggregation of Revenue [Line Items]
Revenue		19.4	32.9	41.0	63.5
Americas | Other Americas
Disaggregation of Revenue [Line Items]
Revenue		362.0	358.8	722.2	720.6
Americas | Other Americas | Reportable Subsegments [Member]
Disaggregation of Revenue [Line Items]
Revenue		362.0	358.8	722.2	720.6
Americas | Other Americas | Services transferred over time
Disaggregation of Revenue [Line Items]
Revenue		354.5	350.7	707.4	705.7
Americas | Other Americas | Services transferred at a point in time
Disaggregation of Revenue [Line Items]
Revenue		7.5	8.1	14.8	14.9
Americas | Staffing and Interim
Disaggregation of Revenue [Line Items]
Revenue		994.5	1,135.0	2,017.2	2,264.6
Americas | Staffing and Interim | United States
Disaggregation of Revenue [Line Items]
Revenue		658.2	803.1	1,345.3	1,595.8
Americas | Staffing and Interim | Other Americas
Disaggregation of Revenue [Line Items]
Revenue		336.3	331.9	671.9	668.8
Americas | Outcome-Based Solutions and Consulting
Disaggregation of Revenue [Line Items]
Revenue		16.5	18.0	31.8	34.3
Americas | Outcome-Based Solutions and Consulting | United States
Disaggregation of Revenue [Line Items]
Revenue		5.0	5.5	9.2	9.8
Americas | Outcome-Based Solutions and Consulting | Other Americas
Disaggregation of Revenue [Line Items]
Revenue		11.5	12.5	22.6	24.5
Americas | Permanent Recruitment
Disaggregation of Revenue [Line Items]
Revenue		43.7	70.9	93.2	136.3
Americas | Permanent Recruitment | United States
Disaggregation of Revenue [Line Items]
Revenue		32.0	58.0	69.8	112.2
Americas | Permanent Recruitment | Other Americas
Disaggregation of Revenue [Line Items]
Revenue		11.7	12.9	23.4	24.1
Americas | Other
Disaggregation of Revenue [Line Items]
Revenue		44.0	38.8	86.7	78.7
Americas | Other | United States
Disaggregation of Revenue [Line Items]
Revenue		41.5	37.3	82.4	75.5
Americas | Other | Other Americas
Disaggregation of Revenue [Line Items]
Revenue		2.5	1.5	4.3	3.2
Southern Europe
Disaggregation of Revenue [Line Items]
Revenue		2,226.9	2,201.4	4,294.8	4,395.3
Southern Europe | Reportable Subsegments [Member]
Disaggregation of Revenue [Line Items]
Revenue		2,226.9	2,201.4	4,294.8	4,395.3
Southern Europe | Services transferred over time
Disaggregation of Revenue [Line Items]
Revenue		2,185.3	2,160.2	4,210.9	4,312.9
Southern Europe | Services transferred at a point in time
Disaggregation of Revenue [Line Items]
Revenue		41.6	41.2	83.9	82.4
Southern Europe | France
Disaggregation of Revenue [Line Items]
Revenue		1,278.2	1,238.2	2,447.5	2,430.6
Southern Europe | France | Reportable Subsegments [Member]
Disaggregation of Revenue [Line Items]
Revenue		1,278.2	1,238.2	2,447.5	2,430.6
Southern Europe | France | Services transferred over time
Disaggregation of Revenue [Line Items]
Revenue		1,263.5	1,223.4	2,417.6	2,400.4
Southern Europe | France | Services transferred at a point in time
Disaggregation of Revenue [Line Items]
Revenue		14.7	14.8	29.9	30.2
Southern Europe | Italy
Disaggregation of Revenue [Line Items]
Revenue		457.8	454.3	880.0	899.3
Southern Europe | Italy | Reportable Subsegments [Member]
Disaggregation of Revenue [Line Items]
Revenue		457.8	454.3	880.0	899.3
Southern Europe | Italy | Services transferred over time
Disaggregation of Revenue [Line Items]
Revenue		443.5	440.9	851.7	873.3
Southern Europe | Italy | Services transferred at a point in time
Disaggregation of Revenue [Line Items]
Revenue		14.3	13.4	28.3	26.0
Southern Europe | Other Southern Europe
Disaggregation of Revenue [Line Items]
Revenue		490.9	508.9	967.3	1,065.4
Southern Europe | Other Southern Europe | Reportable Subsegments [Member]
Disaggregation of Revenue [Line Items]
Revenue		490.9	508.9	967.3	1,065.4
Southern Europe | Other Southern Europe | Services transferred over time
Disaggregation of Revenue [Line Items]
Revenue		478.3	495.9	941.6	1,039.2
Southern Europe | Other Southern Europe | Services transferred at a point in time
Disaggregation of Revenue [Line Items]
Revenue		12.6	13.0	25.7	26.2
Southern Europe | Staffing and Interim
Disaggregation of Revenue [Line Items]
Revenue		1,989.0	1,976.8	3,816.0	3,939.6
Southern Europe | Staffing and Interim | France
Disaggregation of Revenue [Line Items]
Revenue		1,172.8	1,149.9	2,234.5	2,251.4
Southern Europe | Staffing and Interim | Italy
Disaggregation of Revenue [Line Items]
Revenue		425.6	423.9	818.3	841.7
Southern Europe | Staffing and Interim | Other Southern Europe
Disaggregation of Revenue [Line Items]
Revenue		390.6	403.0	763.2	846.5
Southern Europe | Outcome-Based Solutions and Consulting
Disaggregation of Revenue [Line Items]
Revenue		158.7	164.7	321.9	337.2
Southern Europe | Outcome-Based Solutions and Consulting | France
Disaggregation of Revenue [Line Items]
Revenue		71.2	68.3	144.4	138.6
Southern Europe | Outcome-Based Solutions and Consulting | Italy
Disaggregation of Revenue [Line Items]
Revenue		10.2	9.2	19.6	17.3
Southern Europe | Outcome-Based Solutions and Consulting | Other Southern Europe
Disaggregation of Revenue [Line Items]
Revenue		77.3	87.2	157.9	181.3
Southern Europe | Permanent Recruitment
Disaggregation of Revenue [Line Items]
Revenue		47.0	46.8	94.4	92.8
Southern Europe | Permanent Recruitment | France
Disaggregation of Revenue [Line Items]
Revenue		16.2	16.4	32.7	32.9
Southern Europe | Permanent Recruitment | Italy
Disaggregation of Revenue [Line Items]
Revenue		15.3	14.5	30.3	28.2
Southern Europe | Permanent Recruitment | Other Southern Europe
Disaggregation of Revenue [Line Items]
Revenue		15.5	15.9	31.4	31.7
Southern Europe | Other
Disaggregation of Revenue [Line Items]
Revenue		32.2	13.1	62.5	25.7
Southern Europe | Other | France
Disaggregation of Revenue [Line Items]
Revenue		18.0	3.6	35.9	7.7
Southern Europe | Other | Italy
Disaggregation of Revenue [Line Items]
Revenue		6.7	6.7	11.8	12.1
Southern Europe | Other | Other Southern Europe
Disaggregation of Revenue [Line Items]
Revenue		7.5	2.8	14.8	5.9
Northern Europe
Disaggregation of Revenue [Line Items]
Revenue		952.5	1,027.1	1,920.1	2,121.6
Northern Europe | Reportable Subsegments [Member]
Disaggregation of Revenue [Line Items]
Revenue		952.5	1,027.1	1,920.1	2,121.6
Northern Europe | Services transferred over time
Disaggregation of Revenue [Line Items]
Revenue		921.3	988.7	1,854.4	2,045.9
Northern Europe | Services transferred at a point in time
Disaggregation of Revenue [Line Items]
Revenue		31.2	38.4	65.7	75.7
Northern Europe | Staffing and Interim
Disaggregation of Revenue [Line Items]
Revenue		804.8	874.0	1,615.4	1,812.1	$ 26.2
Northern Europe | Outcome-Based Solutions and Consulting
Disaggregation of Revenue [Line Items]
Revenue		82.9	78.9	172.3	172.9
Northern Europe | Permanent Recruitment
Disaggregation of Revenue [Line Items]
Revenue		39.6	47.0	83.0	92.3
Northern Europe | Other
Disaggregation of Revenue [Line Items]
Revenue		25.2	27.2	49.4	44.3
APME
Disaggregation of Revenue [Line Items]
Revenue		599.4	603.7	1,205.3	1,221.9
APME | Reportable Subsegments [Member]
Disaggregation of Revenue [Line Items]
Revenue		599.4	603.7	1,205.3	1,221.9
APME | Services transferred over time
Disaggregation of Revenue [Line Items]
Revenue		578.4	580.5	1,163.0	1,177.6
APME | Services transferred at a point in time
Disaggregation of Revenue [Line Items]
Revenue		21.0	23.2	42.3	44.3
APME | Staffing and Interim
Disaggregation of Revenue [Line Items]
Revenue		453.2	455.6	908.1	918.7
APME | Outcome-Based Solutions and Consulting
Disaggregation of Revenue [Line Items]
Revenue		97.5	98.8	198.4	208.1
APME | Permanent Recruitment
Disaggregation of Revenue [Line Items]
Revenue		36.5	40.5	75.5	77.7
APME | Other
Disaggregation of Revenue [Line Items]
Revenue		12.2	8.8	23.3	17.4
Northern Europe and APME
Disaggregation of Revenue [Line Items]
Revenue		4,877.5	5,094.9	9,649.1	10,252.7
Northern Europe and APME | Reportable Subsegments [Member]
Disaggregation of Revenue [Line Items]
Revenue		4,877.5	5,094.9	9,649.1	10,252.7
Northern Europe and APME | Services transferred over time
Disaggregation of Revenue [Line Items]
Revenue		4,756.8	4,951.1	9,401.4	9,971.9
Northern Europe and APME | Services transferred at a point in time
Disaggregation of Revenue [Line Items]
Revenue		120.7	143.8	247.7	280.8
Northern Europe and APME | Staffing and Interim
Disaggregation of Revenue [Line Items]
Revenue		4,241.5	4,441.4	8,356.7	8,935.0
Northern Europe and APME | Outcome-Based Solutions and Consulting
Disaggregation of Revenue [Line Items]
Revenue		355.6	360.4	724.4	752.5
Northern Europe and APME | Permanent Recruitment
Disaggregation of Revenue [Line Items]
Revenue		166.8	205.2	346.1	399.1
Northern Europe and APME | Other
Disaggregation of Revenue [Line Items]
Revenue		$ 113.6	$ 87.9	$ 221.9	$ 166.1

[1] Our consolidated revenues from services include fees received from our franchise offices of $3.3 and $3.9 for the three months ended June 30, 2023 and 2022, respectively, and $7.2 and $7.5 for the six months ended June 30, 2023 and 2022, respectively. These fees are primarily based on revenues generated by the franchise offices, which were $250.6 and $275.6 for the three months ended June 30, 2023 and 2022, respectively, and $500.8 and $540.8 for the six months ended June 30, 2023 and 2022, respectively.

[2] In the United States, revenues from services included fees received from the related franchise offices of $2.6 and $3.1 for the three months ended June 30, 2023 and 2022, respectively, and $5.8 and $6.0 for the six months ended June 30, 2023 and 2022, respectively. These fees are primarily based on revenues generated by the franchise offices, which were $100.8 and $128.1 for the three months ended June 30, 2023 and 2022, respectively, and $200.1 and $238.9 for the six months ended June 30, 2023 and 2022, respectively.