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		Sep. 30, 2018		Dec. 31, 2017
Guarantor Obligations [Line Items]
Carrying Value		$ (74)		$ 303
Notional/maximum exposure to loss		56,585	[1]	51,036
Credit derivatives [Member]
Guarantor Obligations [Line Items]
Carrying Value	[2],[3]	(74)		303
Notional/maximum exposure to loss	[2],[3]	47,729		42,328
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]	5,216		5,128
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]	$ 3,640		$ 3,580

[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 $24,051 million and $25,639 million of notional issued for the benefit of HSBC affiliates at September 30, 2018 and December 31, 2017, 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 $1,245 million and $1,264 million of both financial and performance standby letters of credit issued for the benefit of HSBC affiliates at September 30, 2018 and December 31, 2017, respectively.