Equity Securities - (Summary of Changes in Carrying Amounts of Non Marketable Equity Securities) (Detail) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2024	Mar. 31, 2023
Equity Securities Without Readily Determinable Fair Value [Line Items]
Carrying amount, beginning of period	$ 224.1
Carrying amount, end of period	226.1
Non Marketable Equity Securities
Equity Securities Without Readily Determinable Fair Value [Line Items]
Carrying amount, beginning of period	224.1	$ 395.8
Net additions	1.8	6.1
Gross unrealized gains	0.2	0.0
Gross unrealized losses and impairments	0.0	(17.2)
Carrying amount, end of period	$ 226.1	$ 384.7