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Equity Securities - (Summary of Investments in Non Marketable Equity Securities) (Detail) - USD ($) $ in Millions | Jun. 30, 2023 | Dec. 31, 2022
--- | --- | ---
Equity Securities Without Readily Determinable Fair Value [Line Items] |  |
Carrying amount | $ 362.9 | $ 395.8
Non Marketable Equity Securities |  |
Equity Securities Without Readily Determinable Fair Value [Line Items] |  |
Cost | 314.2 | 307.2
Unrealized gains | 48.7 | 88.6
Carrying amount | $ 362.9 | $ 395.8

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