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Equity Securities - (Summary of Cumulative Gross Unrealized Gains and Cumulative Gross Unrealized Losses and Impairments) (Details) - Non Marketable Equity Securities - USD ($)
$ in Millions
Sep. 30, 2025
Dec. 31, 2024
Equity Securities without Readily Determinable Fair Value [Line Items]    
Cumulative gross unrealized gains $ 247.3 $ 244.8
Cumulative gross unrealized losses and impairments $ 356.3 $ 351.6