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Equity Securities - (Summary of Investments in Equity Securities, by Classification) (Detail) - USD ($)
$ in Millions
Dec. 31, 2023
Dec. 31, 2022
Investments, Debt and Equity Securities [Abstract]    
Marketable equity securities $ 436.9 $ 279.5
Non-marketable equity securities 224.1 395.8
Equity method investments 74.6 78.9
Equity Securities $ 735.6 $ 754.2