Related Party Transactions - Related Party Balances and Income and (Expense) Generated by Related Party Transactions (Detail) (USD $) In Millions, unless otherwise specified	3 Months Ended				9 Months Ended
	Sep. 30, 2013		Sep. 30, 2012		Sep. 30, 2013		Sep. 30, 2012		Dec. 31, 2012
Assets:
Cash	$ 225				$ 225				$ 197
Securities purchased under agreements to resell	6,196				6,196				2,160
Other assets	1,580				1,580				1,264
Total assets	40,979				40,979				46,778
Liabilities:
Due to affiliates	8,965				8,965				9,089
Derivative related liability	1				1				22
Other liabilities	1,222				1,222				1,372
Total liabilities	34,249				34,249				40,673
Income/(Expense):
Servicing and other fees from HSBC affiliates	6		8		19		26
Support services from HSBC affiliates	(78)		(84)		(213)		(229)
HSBC affiliates [Member]
Assets:
Cash	226				226				193
Securities purchased under agreements to resell	6,196	[1]			6,196	[1]			2,160	[1]
Other assets	51				51				105
Total assets	6,473				6,473				2,458
Liabilities:
Due to affiliates	8,965	[2]			8,965	[2]			9,089	[2]
Derivative related liability	0				0				18
Other liabilities	0				0				83
Total liabilities	8,965				8,965				9,190
Income/(Expense):
Interest income from HSBC affiliates	1		1		3		3
Interest expense paid to HSBC affiliates	(113)	[3]	(140)	[3]	(371)	[3]	(420)	[3]
Net interest income (loss)	(112)		(139)		(368)		(417)
Servicing and other fees from HSBC affiliates	6		8		19		26
Support services from HSBC affiliates	(78)		(84)		(213)		(229)
Stock based compensation expense with HSBC	1	[4]	(2)	[4]	(3)	[4]	(6)	[4]
HSBC affiliates [Member] | Borrowings [Member]
Income/(Expense):
Gain (loss) on FVO debt with affiliate	$ (16)		$ (35)		$ 21		$ (54)

[1] Securities under an agreement to resell are purchased from HSBC Securities (USA) Inc. ("HSI") and generally have terms of 90 days or less. The collateral underlying the securities purchased under agreements to resell, however, is not with HSI. Interest income recognized on these securities is reflected as interest income from HSBC affiliate in the table below.

[2] Due to affiliates includes amounts owed to HSBC and its subsidiaries as a result of direct debt issuances as well as HSBC's ownership of our subordinated debt and excludes preferred stock.

[3] Includes interest expense paid to HSBC affiliates for debt held by HSBC affiliates as well as net interest paid to or received from HSBC affiliates on risk management hedges related to non-affiliated debt.

[4] Employees participate in one or more stock compensation plans sponsored by HSBC. These expenses are included in Salary and employee benefits in our consolidated statement of income (loss). Employees also participate in a defined benefit pension plan and other postretirement benefit plans sponsored by HSBC North America which are discussed in Note 10, “Pension and Other Postretirement Benefits.”