Segment Data - Schedule of Segment Data (Details) - USD ($) $ in Millions		3 Months Ended			6 Months Ended
		Jun. 30, 2024	Jun. 30, 2023		Jun. 30, 2024	Jun. 30, 2023
Segment Reporting Information [Line Items]
Revenues from services	[1]	$ 4,520.7	$ 4,856.1	[2]	$ 8,924.0	$ 9,608.4	[3]
Corporate expenses		(41.7)	(35.5)		(83.4)	(73.4)
Intangible asset amortization expense		(8.1)	(8.7)		(16.4)	(17.5)
Operating profit		101.1	107.6		167.0	225.5
Interest and other expenses, net		(8.7)	(11.8)		(17.1)	(19.3)
Earnings before income taxes		92.4	95.8		149.9	206.2
Americas
Segment Reporting Information [Line Items]
Operating unit profit	[4]	45.1	43.2		71.2	91.8
Southern Europe
Segment Reporting Information [Line Items]
Operating unit profit	[4]	83.2	92.6		153.1	182.5
Northern Europe
Segment Reporting Information [Line Items]
Operating unit profit	[4]	(2.4)	(9.7)		(2.4)	(4.7)
APME
Segment Reporting Information [Line Items]
Operating unit profit	[4]	25.0	25.7		44.9	46.8
Northern Europe and APME
Segment Reporting Information [Line Items]
Operating unit profit	[4]	150.9	151.8		266.8	316.4
Intersegment Eliminations [Member]
Segment Reporting Information [Line Items]
Revenues from services		(20.4)	(21.4)	[2]	(40.2)	(40.7)	[3]
United States | Americas
Segment Reporting Information [Line Items]
Revenues from services		697.0	709.1	[5]	1,377.4	1,450.7	[6]
Other Americas | Americas
Segment Reporting Information [Line Items]
Revenues from services		367.4	389.6	[5]	723.4	778.2	[6]
France | Southern Europe
Segment Reporting Information [Line Items]
Revenues from services		1,184.9	1,278.2	[5]	2,304.2	2,447.5	[6]
Italy | Southern Europe
Segment Reporting Information [Line Items]
Revenues from services		434.9	457.8	[5]	839.2	880.0	[6]
Other Southern Europe | Southern Europe
Segment Reporting Information [Line Items]
Revenues from services		478.2	490.9	[5]	935.9	967.3	[6]
Reportable subsegments | Americas
Segment Reporting Information [Line Items]
Revenues from services		1,064.4	1,098.7	[2]	2,100.8	2,228.9	[3]
Reportable subsegments | Southern Europe
Segment Reporting Information [Line Items]
Revenues from services		2,098.0	2,226.9	[2]	4,079.3	4,294.8	[3]
Reportable subsegments | Northern Europe
Segment Reporting Information [Line Items]
Revenues from services		837.3	952.5	[2]	1,707.6	1,920.1	[3]
Reportable subsegments | APME
Segment Reporting Information [Line Items]
Revenues from services		541.4	599.4	[2]	1,076.5	1,205.3	[3]
Reportable subsegments | Northern Europe and APME
Segment Reporting Information [Line Items]
Revenues from services		4,541.1	4,877.5	[2]	8,964.2	9,649.1	[3]
Reportable subsegments | United States | Americas
Segment Reporting Information [Line Items]
Revenues from services	[7]	697.0	709.1	[2]	1,377.4	1,450.7	[3]
Operating unit profit	[4]	27.4	23.1		39.4	53.1
Reportable subsegments | Other Americas | Americas
Segment Reporting Information [Line Items]
Revenues from services		367.4	389.6	[2]	723.4	778.2	[3]
Operating unit profit	[4]	17.7	20.1		31.8	38.7
Reportable subsegments | France | Southern Europe
Segment Reporting Information [Line Items]
Revenues from services		1,184.9	1,278.2	[2]	2,304.2	2,447.5	[3]
Operating unit profit	[4]	40.3	49.5		73.4	94.4
Reportable subsegments | Italy | Southern Europe
Segment Reporting Information [Line Items]
Revenues from services		434.9	457.8	[2]	839.2	880.0	[3]
Operating unit profit	[4]	34.0	36.3		61.4	67.0
Reportable subsegments | Other Southern Europe | Southern Europe
Segment Reporting Information [Line Items]
Revenues from services		478.2	490.9	[2]	935.9	967.3	[3]
Operating unit profit	[4]	$ 8.9	$ 6.8		$ 18.3	$ 21.1

[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] 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.

[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] 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.

[7] 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.