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
	Mar. 31, 2013		Mar. 31, 2012		Dec. 31, 2012
Related Party Transaction [Line Items]
Due To Affiliate Carried At Fair Value	$ 511				$ 514
Assets:
Cash	545				197
Securities purchased under agreements to resell	3,275				2,160
Derivative related assets	131				0
Other assets	1,639				1,264
Total assets	44,906				46,778
Liabilities:
Due to affiliates (includes $511 million and $514 million at March 31, 2013 and December 31, 2012 carried at fair value, respectively)	9,085				9,089
Derivative related liabilities	1				22
Other liabilities	1,460				1,372
Total liabilities	38,579				40,673
Servicing and other fees from HSBC affiliates:
Total servicing and other fees from HSBC affiliates	7		9
Support services from HSBC affiliates	(68)		(66)
HSBC affiliates [Member]
Assets:
Cash	294				193
Securities purchased under agreements to resell	3,275				2,160
Derivative related assets	131				0
Other assets	125				105
Total assets	3,825				2,458
Liabilities:
Due to affiliates (includes $511 million and $514 million at March 31, 2013 and December 31, 2012 carried at fair value, respectively)	9,085				9,089
Derivative related liabilities	0				18
Other liabilities	(56)	[1]			83	[1]
Total liabilities	9,029				9,190
Income/(Expense):
Interest income from HSBC affiliates	1		1
Interest expense paid to HSBC affiliates	(139)	[2]	(139)	[2]
Net interest income (loss)	(138)		(138)
Servicing and other fees from HSBC affiliates:
Real estate secured servicing and related fees from HSBC Bank USA	3		3
Other servicing, processing and support revenues	1		2
HSBC Technology and Services (USA) Inc. (HTSU) administrative fees and rental revenue	3	[3]	3	[3]
Total servicing and other fees from HSBC affiliates	7		8
Support services from HSBC affiliates	(68)		(66)
Stock based compensation expense with HSBC	(2)		(1)
Due to affiliates	511				514
Borrowings [Member] | HSBC affiliates [Member]
Income/(Expense):
Gain (Loss) on FVO debt with affiliate	3		(14)
Accrued Income Receivable [Member] | HSBC affiliates [Member]
Liabilities:
Other liabilities	$ 95				$ 0

[1] Other liabilities includes $95 million at March 31, 2013 related to accrued interest receivable on derivative positions with affiliates. There were no similar balances at December 31, 2012.Three Months Ended March 31, 2013 2012 (in millions)Income/(Expense): Interest income from HSBC affiliates$1 $1Interest expense paid to HSBC affiliates(1)(139) (139)Net interest income (loss)$(138) $(138)Gain (loss) on FVO debt with affiliate$3 $(14)HSBC affiliate income: Servicing and other fees from HSBC affiliates: Real estate secured servicing and related fees from HSBC Bank USA$3 $3Other servicing, processing and support revenues1 2HSBC Technology and Services (USA) Inc. (“HTSU”) administrative fees and rental revenue(2)3 3Total servicing and other fees from HSBC affiliates$7 $8Support services from HSBC affiliates$(68) $(66)Stock based compensation expense with HSBC$(2) $(1)

[2] 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 positions related to non-affiliated debt.

[3] Rental revenue/(expense) from HTSU totaled $3 million and $3 million during the three months ended March 31, 2013 and 2012, respectively.