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				6 Months Ended
	Jun. 30, 2013		Jun. 30, 2012		Jun. 30, 2013		Jun. 30, 2012		Dec. 31, 2012
Assets:
Cash	$ 261				$ 261				$ 197
Securities purchased under agreements to resell	5,342				5,342				2,160
Other assets	1,789				1,789				1,264
Total assets	42,047				42,047				46,778
Liabilities:
Due to affiliates (includes $478 million and $514 million at June 30, 2013 and December 31, 2012 carried at fair value, respectively)	8,250				8,250				9,089
Derivative related liability	3				3				22
Other liabilities	1,474				1,474				1,372
Total liabilities	35,488				35,488				40,673
Servicing and other fees from HSBC affiliates:
Total servicing and other fees from HSBC affiliates	6		9		13		18
Support services from HSBC affiliates	(67)		(79)		(135)		(145)
HSBC affiliates [Member]
Assets:
Cash	258				258				193
Securities purchased under agreements to resell	5,342				5,342				2,160
Other assets	20				20				105
Total assets	5,620				5,620				2,458
Liabilities:
Due to affiliates (includes $478 million and $514 million at June 30, 2013 and December 31, 2012 carried at fair value, respectively)	8,250				8,250				9,089
Derivative related liability	0				0				18
Other liabilities	7	[1]			7	[1]			83	[1]
Total liabilities	8,257				8,257				9,190
Income/(Expense):
Interest income from HSBC affiliates	1		1		2		2
Interest expense paid to HSBC affiliates	(119)	[2]	(141)	[2]	(258)	[2]	(280)	[2]
Net interest income (loss)	(118)		(140)		(256)		(278)
Servicing and other fees from HSBC affiliates:
Real estate secured servicing and related fees from HSBC Bank USA	2		2		5		5
Other servicing, processing and support revenues	1		3		2		5
HSBC Technology and Services (USA) Inc. (HTSU) administrative fees and rental revenue	3	[3]	4	[3]	6	[3]	8	[3]
Total servicing and other fees from HSBC affiliates	6		9		13		18
Support services from HSBC affiliates	(67)		(79)		(135)		(145)
Stock based compensation expense with HSBC	(2)		(2)		(4)		(4)
HSBC affiliates [Member] | Borrowings [Member]
Income/(Expense):
Gain (loss) on FVO debt with affiliate	34		(5)		37		(19)
HSBC affiliates [Member] | Accrued Income Receivable [Member]
Liabilities:
Other liabilities	$ 54				$ 54				$ 0

[1] Other liabilities includes $54 million at June 30, 2013 related to accrued interest receivable on derivative positions with affiliates. There were no similar balances at December 31, 2012. Three Months EndedJune 30, Six Months EndedJune 30, 2013 2012 2013 2012 (in millions)Income/(Expense): Interest income from HSBC affiliates$1 $1 $2 $2Interest expense paid to HSBC affiliates(1)(119) (141) (258) (280)Net interest income (loss)$(118) $(140) $(256) $(278)Gain (loss) on FVO debt with affiliate$34 $(5) $37 $(19)HSBC affiliate income: Servicing and other fees from HSBC affiliates: Real estate secured servicing and related fees from HSBC Bank USA$2 $2 $5 $5Other servicing, processing and support revenues1 3 2 5HSBC Technology and Services (USA) Inc. (“HTSU”) administrative fees and rental revenue(2)3 4 6 8Total servicing and other fees from HSBC affiliates$6 $9 $13 $18Support services from HSBC affiliates$(67) $(79) $(135) $(145)Stock based compensation expense with HSBC$(2) $(2) $(4) $(4)

[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 hedges related to non-affiliated debt.

[3] Rental revenue/(expense) from HTSU totaled $3 million and $6 million during the three and six months ended June 30, 2013, respectively, compared with $4 million and $7 million during the three and six months ended June 30, 2012, respectively.