Goodwill and Acquired Client Relationships - Schedule of Changes in Acquired Client Relationships (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2025	Dec. 31, 2024	Dec. 31, 2023
Carrying Value
Beginning balance, carrying value	$ 1,777.8
Intangible amortization and impairments	(160.3)	$ (29.0)	$ (48.3)
Ending balance, carrying value	1,639.3	1,777.8
Acquired client relationships
Carrying Value
Beginning balance, carrying value	1,777.8	1,812.4
Intangible amortization and impairments	(160.3)	(29.0)
Foreign currency translation	21.8	(5.6)
Ending balance, carrying value	1,639.3	1,777.8	1,812.4
Acquired client relationships
Indefinite-lived
Beginning balance, carrying value	1,597.5	1,603.1
Intangible impairments	(135.0)
Foreign currency translation	21.8	(5.6)
Ending balance, carrying value	1,484.3	1,597.5	1,603.1
Acquired client relationships
Definite-lived
Beginning balance, gross carrying value	1,255.5	1,260.5
Beginning balance, accumulated amortization	(1,075.2)	(1,051.2)
Beginning balance, net carrying value	180.3	209.3
Intangible amortization and impairments	(25.3)	(29.0)	(48.3)
Foreign currency translation, gross carrying value	11.9	(5.0)
Foreign currency translation, accumulated depreciation	(11.9)	5.0
Ending balance, gross carrying value	1,267.4	1,255.5	1,260.5
Ending balance, accumulated amortization	(1,112.4)	(1,075.2)	(1,051.2)
Ending balance, net carrying value	$ 155.0	$ 180.3	$ 209.3