Guarantee Arrangements, Pledged Assets and Repurchase Agreements - Carrying Value and Contractual Amounts of our Sell Protection Credit Derivatives and Major Off-Balance Sheet Guarantee Arrangements (Detail) - USD ($) $ in Millions		Mar. 31, 2021		Dec. 31, 2020
Guarantor Obligations [Line Items]
Carrying Value		$ 91		$ 144
Notional/maximum exposure to loss		24,660	[1]	28,045
Credit derivatives [Member]
Guarantor Obligations [Line Items]
Carrying Value	[2],[3]	91		144
Notional/maximum exposure to loss	[2],[3]	15,963		19,500
Financial standby letters of credit, net of participations [Member]
Guarantor Obligations [Line Items]
Carrying Value	[4],[5]	0		0
Notional/maximum exposure to loss	[4],[5]	5,832		5,703
Performance standby letters of credit, net of participations [Member]
Guarantor Obligations [Line Items]
Carrying Value	[4],[5]	0		0
Notional/maximum exposure to loss	[4],[5]	2,865		2,842
Affiliated Entity [Member] | Credit derivatives [Member]
Guarantor Obligations [Line Items]
Notional/maximum exposure to loss		13,448		13,550
Affiliated Entity [Member] | Financial and performance standby letters of credit [Member]
Guarantor Obligations [Line Items]
Notional/maximum exposure to loss		$ 1,834		$ 1,836

[1] External ratings for most of the obligors are not available. Presented above are the internal credit ratings which are developed using similar methodologies and rating scale equivalent to external credit ratings for purposes of classification as investment grade and non-investment grade.

[2] For credit derivatives, the maximum loss is represented by the notional amounts without consideration of mitigating effects from collateral or recourse arrangements.

[3] Includes $13,448 million and $13,550 million of notional issued for the benefit of HSBC affiliates at March 31, 2021 and December 31, 2020, respectively.

[4] For standby letters of credit, maximum loss represents losses to be recognized assuming the letters of credit have been fully drawn and the obligors have defaulted with zero recovery.

[5] Includes $1,834 million and $1,836 million of both financial and performance standby letters of credit issued for the benefit of HSBC affiliates at March 31, 2021 and December 31, 2020, respectively.