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Equity Securities - (Summary of Changes in Carrying Amounts of Non Marketable Equity Securities) (Detail) - USD ($) $ in Millions | 12 Months Ended
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Dec. 31, 2024 | Dec. 31, 2023
Equity Securities Without Readily Determinable Fair Value [Line Items] |  |
Carrying amount, beginning of period | $ 224.1 |
Carrying amount, end of period | 202.4 | $ 224.1
Non Marketable Equity Securities |  |
Equity Securities Without Readily Determinable Fair Value [Line Items] |  |
Carrying amount, beginning of period | 224.1 | 395.8
Net additions (disposals) | 6.0 | (4.0)
Gross unrealized gains | 1.5 | 1.5
Gross unrealized losses and impairments | (29.2) | (169.2)
Carrying amount, end of period | $ 202.4 | $ 224.1

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