Securities Purchased Under Agreements to Resell and Securities Sold Under Agreements to Repurchase - Securities Sold under Agreements to Repurchase (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2025	Dec. 31, 2024
Investments, Debt and Equity Securities [Abstract]
Securities Sold Under Agreements to Repurchase	$ 292.2	$ 462.0
Average Balance During the Year	$ 506.8	$ 518.5
Average Interest Rate Paid During the Year	545.26%	632.65%
Maximum Month-End Balance During the Year	$ 841.4	$ 811.8
Securities sold under agreements to repurchase, netting impact	$ 64,300.0	$ 62,400.0
Securities sold under agreements to repurchase, average rate paid excluding netting impact	4.26%	5.21%