Guarantee Arrangements, Pledged Assets and Repurchase Agreements - Additional Information (Detail) - USD ($) $ in Millions		3 Months Ended	12 Months Ended			36 Months Ended
		Dec. 31, 2019	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2007
Guarantor Obligations [Line Items]
Deferred fees		$ 2	$ 2	$ 2
Carrying value of swap		4,807,851	4,807,851	5,556,668
Pledged assets not separately reported, trading assets	[1]	525	525	2,465
Collateral accepted under security resale agreements, fair value		19,174	19,174	13,004
Collateral accepted under security repurchase agreements but not reported on the balance sheet that can be sold or repledged, fair value		18,199	18,199	11,904
Collateral accepted under security repurchase agreements that has been sold or repledged under repurchase agreements or to cover short sales		2,062	2,062	243
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		0	0	822
Trading assets [Member]
Guarantor Obligations [Line Items]
Pledged assets not separately reported, trading assets		336	336	2,464
Other liabilities [Member]
Guarantor Obligations [Line Items]
Allowance for credit losses on unfunded standby letters of credit		26	26	16
Other liabilities [Member] | Standby Letters of Credit [Member]
Guarantor Obligations [Line Items]
Deferred fees		52	52	43
Swap [Member]
Guarantor Obligations [Line Items]
Carrying value of swap		85	85	40
Visa Class B Shares [Member]
Guarantor Obligations [Line Items]
Loss Contingency, Loss in Period		$ 48	$ 52	$ 7
Other Income (Loss) [Member] | Visa Class B Shares [Member]
Guarantor Obligations [Line Items]
Gain on Sale of Investments					$ 312

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