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Goodwill and Acquired Client Relationships - Schedule of Changes in the Components of Acquired Client Relationships (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2023	Jun. 30, 2022	Jun. 30, 2023	Jun. 30, 2022
Total
Beginning balance, net book value			$ 1,876.0
Intangible amortization and impairments	$ (12.5)	$ (12.5)	(25.0)	$ (25.0)
Ending balance, net book value	1,863.1		1,863.1
Acquired Client Relationships
Indefinite-lived
Beginning balance, net book value			1,590.6
Foreign currency translation			15.9
Indefinite-Lived Intangible Assets, Transfers			(4.1)
Ending balance, net book value	1,602.4		1,602.4
Acquired Client Relationships
Definite-lived
Beginning balance, gross book value			1,355.1
Beginning balance, accumulated amortization			(1,069.7)
Beginning balance, net book value			285.4
Intangible amortization and impairments			(25.0)
Foreign currency translation, gross			1.6
Foreign currency translation, accumulated amortization			(1.3)
Foreign currency translation, net			0.3
Transfers, gross book value			(10.3)
Transfers, accumulated amortization			10.3
Ending balance, gross book value	1,346.4		1,346.4
Ending balance, accumulated amortization	(1,085.7)		(1,085.7)
Ending balance, net book value	260.7		260.7
Total
Beginning balance, net book value			1,876.0
Intangible amortization and impairments			(25.0)
Foreign currency translation			16.2
Intangible Assets, Transfers			(4.1)
Ending balance, net book value	$ 1,863.1		$ 1,863.1

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