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 - Additional Information (Detail) - USD ($) $ in Millions		Mar. 31, 2018	Dec. 31, 2017
Guarantor Obligations [Line Items]
Notional/maximum exposure to loss		$ 46,595	$ 51,036
Credit derivatives [Member]
Guarantor Obligations [Line Items]
Notional/maximum exposure to loss	[1],[2]	37,597	42,328
Affiliated Entity [Member] | Credit derivatives [Member]
Guarantor Obligations [Line Items]
Notional/maximum exposure to loss		20,469	25,639
Affiliated Entity [Member] | Financial and performance standby letters of credit [Member]
Guarantor Obligations [Line Items]
Notional/maximum exposure to loss		$ 1,327	$ 1,264

[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.