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Investments - Schedule of Changes in Other Investments (Details) - USD ($)
$ in Millions
 12 Months Ended
Dec. 31, 2024
Dec. 31, 2023
Other Investments [Roll Forward]    
Balance, beginning of period $ 480.9 $ 421.6
Purchases and commitments 92.0 82.5
Sales and distributions (62.2) (57.4)
Net realized and unrealized gains 28.3 34.2
Balance, end of period 539.0 480.9
Equity Securities Without Readily Determinable Fair Value [Roll Forward]    
Balance, beginning of period 50.4 50.4
Purchases and commitments 0.0 0.0
Sales and distributions 0.0 0.0
Net realized and unrealized gains 0.0 0.0
Balance, end of period 50.4 50.4
Fair Value Measured at NAV    
Other Investments [Roll Forward]    
Balance, beginning of period 430.5 371.2
Purchases and commitments 92.0 82.5
Sales and distributions (62.2) (57.4)
Net realized and unrealized gains 28.3 34.2
Balance, end of period $ 488.6 $ 430.5