Equity Securities - (Summary of Changes in Carrying Amounts of Non Marketable Equity Securities) (Detail) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2025	Mar. 31, 2024
Equity Securities Without Readily Determinable Fair Value [Line Items]
Carrying amount, beginning of period	$ 202.4
Carrying amount, end of period	216.6
Non Marketable Equity Securities
Equity Securities Without Readily Determinable Fair Value [Line Items]
Carrying amount, beginning of period	202.4	$ 224.1
Net additions	15.0	1.8
Gross unrealized gains	0.0	0.2
Gross unrealized losses and impairments	(0.8)	0.0
Carrying amount, end of period	$ 216.6	$ 226.1