Equity Securities - (Summary of Changes in Carrying Amount of Non Marketable Equity Securities) (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022
Equity Securities Without Readily Determinable Fair Value [Line Items]
Carrying amount, beginning of period	$ 395.8
Carrying amount, end of period	224.1	$ 395.8
Non Marketable Equity Securities
Equity Securities Without Readily Determinable Fair Value [Line Items]
Carrying amount, beginning of period	395.8	441.3
Net (sales) additions	(4.0)	91.8
Gross unrealized gains	1.5	16.1
Gross unrealized losses and impairments	(169.2)	(153.4)
Carrying amount, end of period	$ 224.1	$ 395.8