v3.26.1
FAIR VALUE OF ASSETS AND LIABILITIES - Tri-Level Hierarchy, Carrying Value (Details) - USD ($)
$ in Millions
Jun. 30, 2026
Dec. 31, 2025
Equity investments:    
Equity investments $ 388.5 $ 414.4
Total 802.3 900.1
Equity method investments 1,054.6 937.1
Other investments 11.5 29.6
Money market funds    
Cash equivalents:    
Money market funds 361.3 477.9
Total return swap related to deferred compensation plans    
Equity investments:    
Total return swap related to deferred compensation plans 52.5 7.8
Seed capital    
Equity investments:    
Equity investments 187.4 286.2
Investments related to deferred compensation plans    
Equity investments:    
Equity investments 136.7 128.2
Other equity securities    
Equity investments:    
Equity investments 64.4  
Quoted Prices in Active Markets for Identical Assets (Level 1)    
Equity investments:    
Total 749.8 745.9
Quoted Prices in Active Markets for Identical Assets (Level 1) | Money market funds    
Cash equivalents:    
Money market funds 361.3 477.9
Quoted Prices in Active Markets for Identical Assets (Level 1) | Total return swap related to deferred compensation plans    
Equity investments:    
Total return swap related to deferred compensation plans 0.0 0.0
Quoted Prices in Active Markets for Identical Assets (Level 1) | Seed capital    
Equity investments:    
Equity investments 187.4 139.8
Quoted Prices in Active Markets for Identical Assets (Level 1) | Investments related to deferred compensation plans    
Equity investments:    
Equity investments 136.7 128.2
Quoted Prices in Active Markets for Identical Assets (Level 1) | Other equity securities    
Equity investments:    
Equity investments 64.4  
Significant Other Observable Inputs (Level 2)    
Equity investments:    
Total 52.5 154.2
Significant Other Observable Inputs (Level 2) | Money market funds    
Cash equivalents:    
Money market funds 0.0 0.0
Significant Other Observable Inputs (Level 2) | Total return swap related to deferred compensation plans    
Equity investments:    
Total return swap related to deferred compensation plans 52.5 7.8
Significant Other Observable Inputs (Level 2) | Seed capital    
Equity investments:    
Equity investments 0.0 146.4
Significant Other Observable Inputs (Level 2) | Investments related to deferred compensation plans    
Equity investments:    
Equity investments 0.0 0.0
Significant Other Observable Inputs (Level 2) | Other equity securities    
Equity investments:    
Equity investments 0.0  
Significant Unobservable Inputs (Level 3)    
Equity investments:    
Total 0.0 0.0
Significant Unobservable Inputs (Level 3) | Money market funds    
Cash equivalents:    
Money market funds 0.0 0.0
Significant Unobservable Inputs (Level 3) | Total return swap related to deferred compensation plans    
Equity investments:    
Total return swap related to deferred compensation plans 0.0 0.0
Significant Unobservable Inputs (Level 3) | Seed capital    
Equity investments:    
Equity investments 0.0 0.0
Significant Unobservable Inputs (Level 3) | Investments related to deferred compensation plans    
Equity investments:    
Equity investments 0.0 $ 0.0
Significant Unobservable Inputs (Level 3) | Other equity securities    
Equity investments:    
Equity investments $ 0.0