Guarantee Arrangements, Pledged Assets and Repurchase Agreements - Summary of Pledged Assets Included in Consolidated Balance Sheet (Detail) - USD ($) $ in Millions	Mar. 31, 2026	Dec. 31, 2025	Mar. 31, 2025
Financial Instruments Owned and Pledged as Collateral [Line Items]
Interest bearing deposits with banks	$ 24,598	$ 23,148
Trading assets	23,604	22,757
Securities available-for-sale	32,551	30,030
Securities held-to-maturity	19,979	18,293
Loans, net	61,586	59,894
Other assets	6,956	6,261
Total assets	174,749	172,410	$ 172,441
Asset Pledged as Collateral
Financial Instruments Owned and Pledged as Collateral [Line Items]
Interest bearing deposits with banks	500	700
Trading assets	3,200	4,000
Securities available-for-sale	16,800	14,600
Securities held-to-maturity	13,500	12,700
Loans, net	21,200	21,600
Other assets	1,000	700
Total assets	$ 56,200	$ 54,300