Segment Data - Schedule of Segment Data (Details) - USD ($) $ in Millions		3 Months Ended		6 Months Ended
		Jun. 30, 2023	Jun. 30, 2022	Jun. 30, 2023	Jun. 30, 2022
Segment Reporting Information [Line Items]
Revenues from services	[1]	$ 4,856.1	$ 5,074.1	$ 9,608.4	$ 10,217.4
Operating unit profit		151.8	225.9	316.4	416.2
Corporate expenses		(35.5)	(35.8)	(73.4)	(77.8)
Intangible asset amortization expense		(8.7)	(9.4)	(17.5)	(19.0)
Operating profit		107.6	180.7	225.5	319.4
Interest and other expenses, net		(11.8)	(6.7)	(19.3)	(9.4)
Earnings before income taxes		95.8	174.0	206.2	310.0
Americas
Segment Reporting Information [Line Items]
Revenues from services		1,098.7	1,262.7	2,228.9	2,513.9
Operating unit profit	[2]	43.2	80.9	91.8	153.7
Southern Europe
Segment Reporting Information [Line Items]
Revenues from services		2,226.9	2,201.4	4,294.8	4,395.3
Operating unit profit		92.6	111.7	182.5	206.9
Northern Europe
Segment Reporting Information [Line Items]
Revenues from services		952.5	1,027.1	1,920.1	2,121.6
Operating unit profit		9.7	10.8	4.7	14.1
APME
Segment Reporting Information [Line Items]
Revenues from services		599.4	603.7	1,205.3	1,221.9
Operating unit profit		25.7	22.5	46.8	41.5
Northern Europe and APME
Segment Reporting Information [Line Items]
Revenues from services		4,877.5	5,094.9	9,649.1	10,252.7
Intercompany Eliminations
Segment Reporting Information [Line Items]
Revenues from services		(21.4)	(20.8)	(40.7)	(35.3)
United States | Americas
Segment Reporting Information [Line Items]
Revenues from services		736.7	903.9	1,506.7	1,793.3
Other Americas | Americas
Segment Reporting Information [Line Items]
Revenues from services		362.0	358.8	722.2	720.6
France | Southern Europe
Segment Reporting Information [Line Items]
Revenues from services		1,278.2	1,238.2	2,447.5	2,430.6
Italy | Southern Europe
Segment Reporting Information [Line Items]
Revenues from services		457.8	454.3	880.0	899.3
Other Southern Europe | Southern Europe
Segment Reporting Information [Line Items]
Revenues from services		490.9	508.9	967.3	1,065.4
Reportable subsegments | Americas
Segment Reporting Information [Line Items]
Revenues from services		1,098.7	1,262.7	2,228.9	2,513.9
Reportable subsegments | Southern Europe
Segment Reporting Information [Line Items]
Revenues from services		2,226.9	2,201.4	4,294.8	4,395.3
Reportable subsegments | Northern Europe
Segment Reporting Information [Line Items]
Revenues from services		952.5	1,027.1	1,920.1	2,121.6
Reportable subsegments | APME
Segment Reporting Information [Line Items]
Revenues from services		599.4	603.7	1,205.3	1,221.9
Reportable subsegments | Northern Europe and APME
Segment Reporting Information [Line Items]
Revenues from services		4,877.5	5,094.9	9,649.1	10,252.7
Reportable subsegments | United States | Americas
Segment Reporting Information [Line Items]
Revenues from services	[3]	736.7	903.9	1,506.7	1,793.3
Operating unit profit	[2]	26.2	64.7	57.3	123.0
Reportable subsegments | Other Americas | Americas
Segment Reporting Information [Line Items]
Revenues from services		362.0	358.8	722.2	720.6
Operating unit profit	[2]	17.0	16.2	34.5	30.7
Reportable subsegments | France | Southern Europe
Segment Reporting Information [Line Items]
Revenues from services		1,278.2	1,238.2	2,447.5	2,430.6
Operating unit profit		49.5	62.3	94.4	111.9
Reportable subsegments | Italy | Southern Europe
Segment Reporting Information [Line Items]
Revenues from services		457.8	454.3	880.0	899.3
Operating unit profit		36.3	35.5	67.0	64.5
Reportable subsegments | Other Southern Europe | Southern Europe
Segment Reporting Information [Line Items]
Revenues from services		490.9	508.9	967.3	1,065.4
Operating unit profit		$ 6.8	$ 13.9	$ 21.1	$ 30.5

[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] We evaluate segment performance based on operating unit profit (“OUP”), which is equal to segment revenues less cost of services and branch and national headquarters operating costs. This profit measure does not include goodwill and intangible asset impairment charges or amortization of intangibles related to acquisitions, corporate expenses, interest and other expense amounts or income taxes.

[3] 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.