Guarantee Arrangements, Pledged Assets and Repurchase Agreements - Narrative (Detail) - USD ($) $ in Millions	36 Months Ended
	Dec. 31, 2007	Mar. 31, 2026	Dec. 31, 2025
Guarantor Obligations [Line Items]
Carrying value of swap		$ 1,685,800	$ 1,405,200
Estimate of reasonably possible loss		100
Fair Value		32,551	30,030
Trading assets		23,604	22,757
Collateral accepted under security resale agreements, fair value		6,900	11,500
Collateral accepted under security repurchase agreements but not reported on the balance sheet that can be sold or repledged, fair value		6,200	10,800
Collateral accepted under security repurchase agreements that has been sold or repledged under repurchase agreements or to cover short sales		100	100
Asset Pledged as Collateral with Right
Guarantor Obligations [Line Items]
Fair Value		2,500	0
Trading assets		2,800	3,500
Obligation to Repurchase Receivables Sold
Guarantor Obligations [Line Items]
Estimated repurchase liability		0	0
HSBC Securities
Guarantor Obligations [Line Items]
Whole loan securitization	$ 24,000
HSBC Securities | Mortgage Securitization Activity Related Litigation
Guarantor Obligations [Line Items]
Mortgage securitization outstanding loan purchase and sold		2,100	2,200
Other liabilities
Guarantor Obligations [Line Items]
Allowance for credit losses on unfunded standby letters of credit		25	18
Other liabilities | Standby Letters of Credit
Guarantor Obligations [Line Items]
Deferred fees		$ 80	$ 71