Guarantee Arrangements, Pledged Assets and Repurchase Agreements - Additional Information (Detail) - USD ($) $ in Millions		12 Months Ended			36 Months Ended
		Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2007
Guarantor Obligations [Line Items]
Deferred fees		$ 3	$ 2
Carrying value of swap		2,021,133	4,807,851
Pledged assets not separately reported, trading assets	[1]	1,265	525
Collateral accepted under security resale agreements, fair value		41,447	19,174
Collateral accepted under security repurchase agreements but not reported on the balance sheet that can be sold or repledged, fair value		41,047	18,199
Collateral accepted under security repurchase agreements that has been sold or repledged under repurchase agreements or to cover short sales		4,063	2,062
Visa Class B Shares [Member]
Guarantor Obligations [Line Items]
Loss on Visa shares		9	52	$ 7
HSBC Securities [Member]
Guarantor Obligations [Line Items]
Whole loan securitization					$ 24,000
Securities available-for-sale [Member]
Guarantor Obligations [Line Items]
Securities pledged as collateral that can be sold or repledged by the secured party, fair value		2,077	0
Trading assets [Member]
Guarantor Obligations [Line Items]
Pledged assets not separately reported, trading assets		1,265	336
Other liabilities [Member]
Guarantor Obligations [Line Items]
Allowance for credit losses on unfunded standby letters of credit		32	26
Other liabilities [Member] | Standby Letters of Credit [Member]
Guarantor Obligations [Line Items]
Deferred fees		44	52
Swap [Member]
Guarantor Obligations [Line Items]
Carrying value of swap		67	85
Mortgage Securitization Activity Related Litigation [Member] | HSBC Securities [Member]
Guarantor Obligations [Line Items]
Mortgage securitization outstanding loan purchase and sold		$ 3,100	$ 3,400

[1] Trading assets are primarily pledged against liabilities associated with repurchase agreements.