Segment Data - Schedule of Segment Data (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2025		Dec. 31, 2024		Dec. 31, 2023
Segment Reporting Information [Line Items]
Revenue	$ 17,957.1		$ 17,853.9	[1]	$ 18,914.5
Cost of services	14,959.5		14,767.1		15,556.5
Selling and Administrative Expense	2,847.5		2,780.8		3,102.2
Corporate expenses	(184.7)		(146.1)		(153.7)
Goodwill impairment charges	(88.7)	[2]	0.0		(55.1)
Intangible asset amortization expense	(31.3)	[3]	(32.7)	[4]	(34.6)	[5]
Operating profit	150.1		306.0		255.8
Interest and other expenses, net	(56.7)		(49.2)		(49.9)
Earnings before income taxes	93.4		256.8		205.9
Total assets	9,160.1		8,201.0		8,830.2
Long-lived Assets	555.2	[6]	516.2	[7]	588.6	[8]
Depreciation and amortization expense	86.0		86.6		88.6
Reportable segments
Segment Reporting Information [Line Items]
Total assets	842.0	[9]	329.2	[10]	495.6	[11]
Long-lived Assets	10.4	[6],[9]	7.5	[7],[10]	10.7	[8],[11]
Depreciation and amortization expense	3.5	[9]	4.1	[10]	2.8	[11]
Segment Reconciling Items
Segment Reporting Information [Line Items]
Total assets	0.0	[12]	0.0	[13]	0.0	[14]
Long-lived Assets	0.0	[6],[12]	0.0	[7],[13]	0.0	[8],[14]
Depreciation and amortization expense	31.3	[12]	32.7	[13]	34.6	[14]
Intercompany Eliminations
Segment Reporting Information [Line Items]
Revenue	(31.0)		(54.9)	[1]	(85.9)
Cost of services	(24.9)		(51.3)		(85.9)
Selling and Administrative Expense	(6.1)		(3.6)		0.0
Operating unit profit (OUP)	0.0		0.0		0.0
Americas
Segment Reporting Information [Line Items]
Total assets	3,521.0		3,367.7		3,488.2
Long-lived Assets	91.4	[6]	91.0	[7]	104.4	[8]
Depreciation and amortization expense	11.6		12.3		11.7
Southern Europe
Segment Reporting Information [Line Items]
Total assets	3,685.0		3,291.4	[15]	3,541.0	[16]
Long-lived Assets	280.8	[6]	262.9	[7],[15]	289.4	[8],[16]
Depreciation and amortization expense	22.0		21.1	[15]	19.3	[16]
Northern Europe | Reportable segments
Segment Reporting Information [Line Items]
Total assets	443.9		597.7		586.3
Long-lived Assets	117.2	[6]	115.1	[7]	138.0	[8]
Depreciation and amortization expense	11.8		10.9		13.9
APME | Reportable segments
Segment Reporting Information [Line Items]
Total assets	668.2		615.0		719.1
Long-lived Assets	55.4	[6]	39.7	[7]	46.1	[8]
Depreciation and amortization expense	5.8		5.5		6.3
United States | Americas | Reportable segments
Segment Reporting Information [Line Items]
Total assets	2,973.4		2,902.4		3,050.4
Long-lived Assets	76.4	[6]	77.7	[7]	87.9	[8]
Depreciation and amortization expense	9.2		9.7		9.5
Other Americas | Americas | Reportable segments
Segment Reporting Information [Line Items]
Total assets	547.6		465.3		437.8
Long-lived Assets	15.0	[6]	13.3	[7]	16.5	[8]
Depreciation and amortization expense	2.4		2.6		2.2
France | Southern Europe | Reportable segments
Segment Reporting Information [Line Items]
Total assets	2,236.5		2,021.2	[15]	2,222.4	[16]
Long-lived Assets	180.5	[6]	171.8	[7],[15]	182.9	[8],[16]
Depreciation and amortization expense	15.5		15.2	[15]	12.7	[16]
Italy | Southern Europe | Reportable segments
Segment Reporting Information [Line Items]
Total assets	555.2		479.3	[15]	487.0	[16]
Long-lived Assets	50.1	[6]	45.6	[7],[15]	50.6	[8],[16]
Depreciation and amortization expense	2.1		2.0	[15]	2.2	[16]
Other Southern Europe | Southern Europe
Segment Reporting Information [Line Items]
Total assets	893.3		790.9	[15]	831.6	[16]
Long-lived Assets	50.2	[6]	45.5	[7],[15]	55.9	[8],[16]
Depreciation and amortization expense	4.4		3.9	[15]	4.4	[16]
Reportable subsegments
Segment Reporting Information [Line Items]
Revenue	17,957.1		17,853.9		18,914.5
Cost of services	14,959.5		14,767.1		15,556.3
Selling and Administrative Expense	2,542.8		2,602.0		2,859.0
Operating unit profit (OUP)	454.8		484.8		499.2
Reportable subsegments | Americas
Segment Reporting Information [Line Items]
Revenue	4,348.8		4,224.9	[1]	4,414.8	[17]
Cost of services	3,407.5		3,252.7		3,376.1	[17]
Selling and Administrative Expense	804.4		830.6		873.1	[17]
Operating unit profit (OUP)	136.9		141.6		165.6	[17]
Reportable subsegments | Southern Europe
Segment Reporting Information [Line Items]
Revenue	8,436.3		8,218.3	[1],[18]	8,515.3	[19]
Cost of services	7,236.3		7,017.6	[18]	7,226.9	[19]
Selling and Administrative Expense	939.4		896.6	[18]	930.7	[19]
Operating unit profit (OUP)	260.6		304.1	[18]	357.7	[19]
Reportable subsegments | Northern Europe
Segment Reporting Information [Line Items]
Revenue	3,161.1		3,304.3	[1]	3,748.0
Cost of services	2,639.2		2,728.0		3,099.0
Selling and Administrative Expense	565.2		620.9		765.7
Operating unit profit (OUP)	(43.3)		(44.6)		(116.7)
Reportable subsegments | APME
Segment Reporting Information [Line Items]
Revenue	2,041.9		2,161.3	[1]	2,322.3
Cost of services	1,701.4		1,820.1		1,940.2
Selling and Administrative Expense	239.9		257.5		289.5
Operating unit profit (OUP)	100.6		83.7		92.6
Reportable subsegments | Northern Europe And APME
Segment Reporting Information [Line Items]
Revenue	17,988.1		17,908.8	[1]	19,000.4
Cost of services	14,984.4		14,818.4		15,642.2
Selling and Administrative Expense	2,548.9		2,605.6		2,859.0
Operating unit profit (OUP)	454.8		484.8		499.2
Reportable subsegments | United States | Americas
Segment Reporting Information [Line Items]
Revenue	2,735.4	[20]	2,766.6	[1],[21]	2,866.2	[17]
Cost of services	2,039.5	[20]	2,032.3	[21]	2,081.6	[17]
Selling and Administrative Expense	629.9	[20]	656.6	[21]	690.2	[17]
Operating unit profit (OUP)	66.0	[20]	77.7	[21]	94.4	[17]
Reportable subsegments | Other Americas | Americas
Segment Reporting Information [Line Items]
Revenue	1,613.4		1,458.3	[1]	1,548.6	[17]
Cost of services	1,368.0		1,220.4		1,294.5	[17]
Selling and Administrative Expense	174.5		174.0		182.9	[17]
Operating unit profit (OUP)	70.9		63.9		71.2	[17]
Reportable subsegments | France | Southern Europe
Segment Reporting Information [Line Items]
Revenue	4,459.4		4,531.5	[1],[18]	4,790.1	[19]
Cost of services	3,831.8		3,873.8	[18]	4,076.7	[19]
Selling and Administrative Expense	517.7		508.2	[18]	526.6	[19]
Operating unit profit (OUP)	109.9		149.5	[18]	186.8	[19]
Reportable subsegments | Italy | Southern Europe
Segment Reporting Information [Line Items]
Revenue	1,822.1		1,677.0	[1],[18]	1,708.8	[19]
Cost of services	1,533.3		1,398.1	[18]	1,418.4	[19]
Selling and Administrative Expense	173.0		165.8	[18]	165.7	[19]
Operating unit profit (OUP)	115.8		113.1	[18]	124.7	[19]
Reportable subsegments | Other Southern Europe | Southern Europe
Segment Reporting Information [Line Items]
Revenue	2,154.8		2,009.8	[1],[18]	2,016.4	[19]
Cost of services	1,871.2		1,745.7	[18]	1,731.8	[19]
Selling and Administrative Expense	248.7		222.6	[18]	238.4	[19]
Operating unit profit (OUP)	$ 34.9		$ 41.5	[18]	$ 46.2	[19]

[1] Effective January 1, 2025, our segment reporting was realigned to include our Morocco business within Other Southern Europe. Accordingly, France is now adjusted to exclude Morocco. All previously reported results have been recast to conform to the current year presentation.

[2] Impairment charges for the year ended December 31, 2025 consist of a goodwill impairment related to our investments in Switzerland and the United Kingdom and an impairment of an indefinite-lived intangible asset in our Switzerland business.

[3] Intangible asset amortization related to acquisitions is excluded from operating costs within the reportable segments and corporate expenses, and shown separately.

[4] Intangible asset amortization related to acquisitions is excluded from operating costs within the reportable segments and corporate expenses, and shown separately.

[5] Intangible asset amortization related to acquisitions is excluded from operating costs within the reportable segments and corporate expenses, and shown separately.

[6] Long-lived assets consist of net property and equipment, net capitalized software and right-of-use assets.

[7] Long-lived assets consist of net property and equipment, net capitalized software and right-of-use assets.

[8] Long-lived assets consist of net property and equipment, net capitalized software and right-of-use assets.

[9] Corporate assets include assets that were not used in the operations of any segment. The most significant assets were purchased intangibles and cash, including the proceeds from the €500.0 Euro notes issued in December 2025.

[10] Corporate assets include assets that were not used in the operations of any segment, the most significant of which were purchased intangibles and cash.

[11] Corporate assets include assets that were not used in the operations of any segment, the most significant of which were purchased intangibles and cash.

[12] Intangible asset amortization related to acquisitions is excluded from operating costs within the reportable segments and corporate expenses, and shown separately.

[13] Intangible asset amortization related to acquisitions is excluded from operating costs within the reportable segments and corporate expenses, and shown separately.

[14] Intangible asset amortization related to acquisitions is excluded from operating costs within the reportable segments and corporate expenses, and shown separately.

[15] Effective January 1, 2025, our segment reporting was realigned to include our Morocco business within Other Southern Europe. Accordingly, France is now adjusted to exclude Morocco's total assets.

[16] Effective January 1, 2025, our segment reporting was realigned to include our Morocco business within Other Southern Europe. Accordingly, France is now adjusted to exclude Morocco's total assets.

[17] The United States revenues above represent revenues from our company-owned branches and franchise fees received from our franchise operations, which were $11.9 for 2023.

[18] Effective January 1, 2025, our segment reporting was realigned to include our Morocco business within Other Southern Europe. Accordingly, France is now adjusted to exclude Morocco. All previously reported results have been recast to conform to the current year presentation.

[19] Effective January 1, 2025, our segment reporting was realigned to include our Morocco business within Other Southern Europe. Accordingly, France is now adjusted to exclude Morocco. All previously reported results have been recast to conform to the current year presentation.

[20] The United States revenues above represent revenues from our company-owned branches and franchise fees received from our franchise operations, which were $10.1 for 2025.

[21] The United States revenues above represent revenues from our company-owned branches and franchise fees received from our franchise operations, which were $10.7 for 2024.