GOODWILL AND INTANGIBLE ASSETS - Goodwill and Intangible Assets (Details) - USD ($) $ in Millions	Sep. 30, 2025	Dec. 31, 2024
Schedule of Intangible Assets and Goodwill [Line Items]
Goodwill	$ 2,642.8	$ 2,642.8
Total	2,937.4	3,010.9
Investment Advisory Agreements
Schedule of Intangible Assets and Goodwill [Line Items]
Definite-lived intangible assets - investment advisory agreements	146.3	216.5
Trade Name
Schedule of Intangible Assets and Goodwill [Line Items]
Indefinite-lived intangible assets	86.0	86.0
Investment Advisory Agreements
Schedule of Intangible Assets and Goodwill [Line Items]
Indefinite-lived intangible assets	$ 62.3	$ 65.6