Summary of Significant Accounting Policies - Additional Information (Details) $ / shares in Units, $ in Millions		3 Months Ended					12 Months Ended
		Dec. 31, 2022 USD ($) Office Country shares		Sep. 30, 2022 USD ($)	Sep. 30, 2021 USD ($)	Sep. 30, 2020 USD ($)	Dec. 31, 2022 USD ($) Office Country $ / shares shares		Dec. 31, 2021 USD ($) $ / shares shares		Dec. 31, 2020 USD ($) $ / shares shares	Aug. 31, 2021 shares	Aug. 31, 2019 shares	Aug. 31, 2018 shares
Accounting Policies [Line Items]
Number of offices worldwide (over) | Office		2,200					2,200
Number of countries and territories | Country		75					75
Investments value		$ 95.8					$ 95.8		$ 114.2
Unremitted earning from investments							$ 4.3		11.8
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		35.6					$ 35.6		34.8
Advertising expenses							29.6		28.1		$ 22.2
Restructuring costs							3.6		15.2		110.7
Operating lease right-of-use asset impairment							0.0		0.0		27.3
Costs paid, utilized or transferred							13.7		38.0
Reserve will be paid by end of period		13.2					13.2		23.3		46.1
Consolidated amortization expense related to intangibles	[1]						37.1		24.2		27.2
2023		34.6					34.6
2024		32.2					32.2
2025		30.2					30.2
2026		26.7					26.7
2027		26.1					26.1
Goodwill, Impairment Loss				$ 0.0	$ 0.0	$ 0.0	50.0	[2],[3]	0.0		66.8
Goodwill	[2]	1,628.1	[4]				1,628.1	[4]	1,722.2	[4]	1,225.8
Net capitalized software balance		$ 47.7					47.7		38.2
Amortization expense related to capitalized software cost							$ 9.8		$ 5.5		$ 1.8
Shares authorized to be repurchased (in shares) | shares												4,000,000.0	6,000,000.0	6,000,000.0
Shares repurchased (in shares) | shares							3,200,000				3,400,000
Total cost of shares repurchased							$ 270.0				$ 264.7
Dividends declared (in dollars per share) | $ / shares							$ 2.72		$ 2.52		$ 2.26
Total dividend payments							$ 139.9		$ 136.6		$ 129.1
Net earnings, net of tax, attributable to noncontrolling interests							24.6		17.3		39.9
Cloud Computing Arrangements
Accounting Policies [Line Items]
Unamortized Implementation Costs							19.9
Noncontrolling Interests
Accounting Policies [Line Items]
Net earnings, net of tax, attributable to noncontrolling interests							$ 0.8		$ 0.7		$ 4.7
August 2019 Authorization
Accounting Policies [Line Items]
Shares repurchased (in shares) | shares							1,200,000		2,100,000		2,600,000
Total cost of shares repurchased									$ 210.0
Shares remaining authorized for repurchase (in shares) | shares		0					0
August 2018 Authorization
Accounting Policies [Line Items]
Shares repurchased (in shares) | shares											800,000
Shares remaining authorized for repurchase (in shares) | shares		0					0
August 2021 Authorization
Accounting Policies [Line Items]
Shares repurchased (in shares) | shares							2,000,000.0
Shares remaining authorized for repurchase (in shares) | shares		2,000,000.0					2,000,000.0
Buildings
Accounting Policies [Line Items]
Estimated useful lives							40 years
Leasehold Improvements
Accounting Policies [Line Items]
Estimated useful lives							lesser of life of asset or expected lease term
Netherlands
Accounting Policies [Line Items]
Goodwill, Impairment Loss							$ 50.0
Discount rate for goodwill impairment test (as a percent)				1.25
Netherlands | Discount Rates
Accounting Policies [Line Items]
Discount rate for goodwill impairment test (as a percent)		1.35					1.35
Netherlands | Terminal Value Revenue Growth Rate
Accounting Policies [Line Items]
Discount rate for goodwill impairment test (as a percent)		0.20		0.20			0.20
Netherlands | Terminal Value OUP Margin
Accounting Policies [Line Items]
Discount rate for goodwill impairment test (as a percent)		0.40		0.40			0.40
Northern Europe | Netherlands
Accounting Policies [Line Items]
Goodwill, Impairment Loss		$ 50.0
Goodwill		$ 55.1					$ 55.1
Minimum
Accounting Policies [Line Items]
Percentage of goodwill over fair value of reporting unit							20.00%
Remaining lease terms		1 month					1 month
Minimum | Furniture, Fixtures, and Autos
Accounting Policies [Line Items]
Estimated useful lives							3 years
Minimum | Computer Equipment
Accounting Policies [Line Items]
Estimated useful lives							3 years
Minimum | Netherlands
Accounting Policies [Line Items]
Discount rate for goodwill impairment test (as a percent)				0.30
Minimum | Netherlands | Revenue Growth
Accounting Policies [Line Items]
Discount rate for goodwill impairment test (as a percent)		0.00					0.00
Maximum
Accounting Policies [Line Items]
Remaining lease terms		11 years					11 years
Maximum | Furniture, Fixtures, and Autos
Accounting Policies [Line Items]
Estimated useful lives							16 years
Maximum | Computer Equipment
Accounting Policies [Line Items]
Estimated useful lives							16 years
Maximum | Netherlands
Accounting Policies [Line Items]
Discount rate for goodwill impairment test (as a percent)				0.84
Maximum | Netherlands | Revenue Growth
Accounting Policies [Line Items]
Discount rate for goodwill impairment test (as a percent)		0.30					0.30
Customer relationships
Accounting Policies [Line Items]
Useful life							14 years
Other
Accounting Policies [Line Items]
Useful life							4 years
Computer software | Minimum
Accounting Policies [Line Items]
Useful life							3 years
Computer software | Maximum
Accounting Policies [Line Items]
Useful life							0 years
Other Reporting Units | Minimum
Accounting Policies [Line Items]
Percentage of goodwill over fair value of reporting unit							20.00%
Euro-denominated notes | Estimate of fair value measurement | Significant Other Observable Inputs (Level 2)
Accounting Policies [Line Items]
Carrying value of long-term debt		$ 921.7					$ 921.7		1,064.0
Euro-denominated notes | Carrying value | Significant Other Observable Inputs (Level 2)
Accounting Policies [Line Items]
Carrying value of long-term debt		$ 956.6					$ 956.6		$ 1,019.6

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

[2] Balances were net of accumulated impairment loss of $644.2 ($127.0 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, 2021 and December 31, 2021; and $694.2 ($177.0 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, 2022.

[3] The 2022 impairment charge of $50.0 relates to our Netherlands reporting unit, which was recorded during the fourth quarter of 2022. See Note 1 to the Consolidated Financial Statements for further information.

[4] Balances were net of accumulated impairment loss of $694.2 and $644.2 as of December 31, 2022 and 2021, respectively.