Debt Securities (Sales of Debt Securities) (Narrative) (Detail) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2025	Mar. 31, 2024
Debt Securities, Available-for-Sale [Line Items]
Realized losses on sales of debt securities	$ (2.6)	$ (4.2)
Realized gains on sales of debt securities	1.1	0.8
Proceeds from sales of debt securities	$ 266.8	$ 224.5