INVESTMENTS - Details of Company Investments (Details) - USD ($) $ in Millions	Mar. 31, 2024	Dec. 31, 2023
Schedule of Investments [Line Items]
Equity method investments	$ 651.4	$ 631.8
Other	14.9	14.9
Total investments	963.5	919.1
Seed capital
Schedule of Investments [Line Items]
Equity investments	86.0	75.7
Investments related to deferred compensation plans
Schedule of Investments [Line Items]
Equity investments	$ 211.2	$ 196.7