Securities Purchased Under Agreements to Resell and Securities Sold Under Agreements to Repurchase - Securities Purchased under Agreements to Resell (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2025	Dec. 31, 2024
Investments, Debt and Equity Securities [Abstract]
Federal Funds Sold and Securities Purchased under Agreements to Resell	$ 2,654.1	$ 426.0
Average Balance During the Year	$ 1,003.8	$ 727.5
Average Interest Rate Earned During the Year	281.85%	459.13%
Maximum Month-End Balance During the Year	$ 2,654.1	$ 1,034.6
Securities purchased under agreements to resell, netting impact	$ 64,300.0	$ 62,400.0
Securities purchased under agreements to resell, average rate paid excluding netting impact	4.33%	5.29%