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Equity Securities - (Summary of Investments in Non Marketable Equity Securities) (Detail) - USD ($)
$ in Millions
Sep. 30, 2023
Dec. 31, 2022
Equity Securities Without Readily Determinable Fair Value [Line Items]    
Carrying amount $ 226.7 $ 395.8
Non Marketable Equity Securities    
Equity Securities Without Readily Determinable Fair Value [Line Items]    
Cost 300.1 307.2
Unrealized (losses) gains (73.4) 88.6
Carrying amount $ 226.7 $ 395.8