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, 2018	Dec. 31, 2017
Guarantor Obligations [Line Items]
Carrying Value		$ 234	$ 303
Notional/maximum exposure to loss		46,595	51,036
Credit derivatives [Member]
Guarantor Obligations [Line Items]
Carrying Value	[1],[2]	234	303
Notional/maximum exposure to loss	[1],[2]	37,597	42,328
Financial standby letters of credit, net of participations [Member]
Guarantor Obligations [Line Items]
Carrying Value	[3],[4]	0	0
Notional/maximum exposure to loss	[3],[4]	5,533	5,128
Performance standby letters of credit, net of participations [Member]
Guarantor Obligations [Line Items]
Carrying Value	[3],[4]	0	0
Notional/maximum exposure to loss	[3],[4]	$ 3,465	$ 3,580

[1] .

[2] Includes $20,469 million and $25,639 million of notional issued for the benefit of HSBC affiliates at March 31, 2018 and December 31, 2017, respectively.

[3] 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.

[4] Includes $1,327 million and $1,264 million of both financial and performance standby letters of credit issued for the benefit of HSBC affiliates at March 31, 2018 and December 31, 2017, respectively.