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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
	Mar. 31, 2022	Mar. 31, 2021
Total
Beginning balance, net book value	$ 1,966.4
Intangible amortization and impairments	(12.6)	$ (7.5)
Ending balance, net book value	1,943.3
Acquired Client Relationships
Definite-lived
Beginning balance, gross book value	1,364.2
Beginning balance, accumulated amortization	(1,028.1)
Beginning balance, net book value	336.1
Intangible amortization and impairments	(12.3)
Foreign currency translation, gross	(2.8)
Foreign currency translation, accumulated amortization	2.3
Foreign currency translation, net	(0.5)
Ending balance, gross book value	1,361.4
Ending balance, accumulated amortization	(1,038.1)
Ending balance, net book value	323.3
Indefinite-lived
Beginning balance, net book value	1,630.3
Intangible amortization and impairments	(0.3)
Foreign currency translation	(10.0)
Ending balance, net book value	1,620.0
Total
Beginning balance, net book value	1,966.4
Intangible amortization and impairments	(12.6)
Foreign currency translation	(10.5)
Ending balance, net book value	$ 1,943.3

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