Summary of Significant Accounting Policies - Additional Information (Details) $ in Millions	12 Months Ended
	Dec. 31, 2025 USD ($) Office Country		Dec. 31, 2024 USD ($)		Dec. 31, 2023 USD ($)
Accounting Policies [Line Items]
Number of offices worldwide (over) | Office	2,100
Number of countries and territories | Country	70
Investments value	$ 100.2		$ 103.9
Unremitted earning from investments	$ 6.5		16.9
Payment terms	60 days
Description of timing	Our client contracts are generally short-term in nature with a term of one year or less. The timing between satisfaction of the performance obligation, invoicing and payment is not significant.
Deferred revenue	$ 45.6		30.3
Exceeded fair value	10.00%
Advertising expenses	$ 28.1		28.3		$ 28.9
Costs paid, utilized or transferred	72.9		93.7
Reserve will be paid by end of period	35.1
Consolidated amortization expense related to intangibles	31.3	[1]	32.7	[2]	34.6	[3]
2026	27.9
2027	27.1
2028	27.1
2029	26.8
2030	26.3
Goodwill, Impairment Loss	88.7	[4]	0.0		55.1
Goodwill	1,544.6	[5],[6]	1,563.4	[5],[6]	1,586.8
Net capitalized software balance	$ 39.3		36.5
Asset Impairment Charges					2.2
Property, Plant, and Equipment, Useful Life, Term, Description [Extensible Enumeration]	Property, Plant and Equipment, Net
Costs paid or utilized	$ 72.9		93.7
Restructuring reserve	35.1
Cloud Computing Arrangements
Accounting Policies [Line Items]
Unamortized Implementation Costs	$ 166.5		$ 110.8		54.6
Buildings
Accounting Policies [Line Items]
Estimated useful lives	40 years
Minimum
Accounting Policies [Line Items]
Remaining lease terms	1 month
Minimum | Furniture, Fixtures, and Autos
Accounting Policies [Line Items]
Estimated useful lives	3 years
Maximum
Accounting Policies [Line Items]
Remaining lease terms	14 years
Maximum | Computer Equipment
Accounting Policies [Line Items]
Estimated useful lives	16 years
Customer relationships
Accounting Policies [Line Items]
Useful life	15 years		5 years
Computer software | Minimum
Accounting Policies [Line Items]
Useful life	3 years
Computer software | Maximum
Accounting Policies [Line Items]
Useful life	10 years
Euro-denominated notes | Estimate of fair value measurement | Significant Other Observable Inputs (Level 2)
Accounting Policies [Line Items]
Carrying value of long-term debt	$ 1,645.3		$ 928.5
Euro-denominated notes | Carrying value | Significant Other Observable Inputs (Level 2)
Accounting Policies [Line Items]
Carrying value of long-term debt	1,639.0		928.4
Selling and Administrative Expenses
Accounting Policies [Line Items]
Net restructuring costs	64.2		53.6		149.2
Amortization expense related to capitalized software cost	$ 17.2		$ 15.8		$ 13.8
North America | Terminal Value OUP Margin
Accounting Policies [Line Items]
Revenue Growth Percentage	5.00%
United Kingdom
Accounting Policies [Line Items]
Discount Rate	11.40%
Goodwill	$ 78.0
United Kingdom | Terminal Value OUP Margin
Accounting Policies [Line Items]
Revenue Growth Percentage	0.50%
United Kingdom | Northern Europe
Accounting Policies [Line Items]
Goodwill, Impairment Loss	$ 33.4
United Kingdom | Minimum
Accounting Policies [Line Items]
Revenue Growth Percentage	8.40%
United Kingdom | Maximum
Accounting Policies [Line Items]
Revenue Growth Percentage	10.00%
Switzerland
Accounting Policies [Line Items]
Discount Rate	11.20%
Goodwill	$ 35.5
Switzerland | Terminal Value Revenue Growth Rate
Accounting Policies [Line Items]
Revenue Growth Percentage	3.00%
Switzerland | Southern Europe
Accounting Policies [Line Items]
Discount Rate	13.70%
Goodwill, Impairment Loss	$ 24.7
Asset Impairment Charges	$ 30.6
Switzerland | Minimum
Accounting Policies [Line Items]
Revenue Growth Percentage	12.00%
Switzerland | Minimum | Terminal Value OUP Margin
Accounting Policies [Line Items]
Revenue Growth Percentage	1.00%
Switzerland | Maximum
Accounting Policies [Line Items]
Revenue Growth Percentage	12.40%
Switzerland | Maximum | Terminal Value OUP Margin
Accounting Policies [Line Items]
Revenue Growth Percentage	4.00%
United States
Accounting Policies [Line Items]
Discount Rate	9.40%
United States | Minimum
Accounting Policies [Line Items]
Revenue Growth Percentage	1.70%
United States | Maximum
Accounting Policies [Line Items]
Revenue Growth Percentage	8.00%

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

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

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

[4] 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.

[5] Balances were net of accumulated impairment loss of $749.3 ($232.1 related to Northern Europe, $3.8 related to APME, $235.2 related to Right Management and $278.2 related to Corporate) as of both January 1, 2024 and December 31, 2024; and $807.4 ($24.7 related to Southern Europe, $265.5 related to Northern Europe, $3.8 related to APME, $235.2 related to Right Management and $278.2 related to Corporate) as of December 31, 2025.

[6] Balances were net of accumulated impairment loss of $807.4 and $749.3 as of December 31, 2025 and 2024, respectively.