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, 2012	Sep. 30, 2011	Sep. 30, 2012	Sep. 30, 2011	Dec. 31, 2011
Assets:
Cash	$ 729		$ 729		$ 215
Securities purchased under agreements to resell	900		900		920
Derivative related assets	10		10
Other assets	1,486		1,486		1,312
Total assets	47,525		47,525		63,567
Liabilities:
Due to affiliates (includes $501 million and $447 million at September 30, 2012 and December 31, 2011, respectively, carried at fair value)	7,826		7,826		8,262
Derivative related liabilities	9		9		26
Other liabilities	1,258		1,258		1,688
Total liabilities	41,122		41,122		56,641
Income/(Expense):
Gain (loss) on FVO debt with affiliate	(95)	792	(399)	1,008
Servicing and other fees from HSBC affiliates:
Total servicing and other fees from HSBC affiliates	8	4	26	17
Support services from HSBC affiliates	84	68	229	207
Related Parties [Member]
Assets:
Cash	726		726		209
Securities purchased under agreements to resell	900		900		920
Derivative related assets	10		10
Other assets	147		147		124
Total assets	1,783		1,783		1,253
Liabilities:
Due to affiliates (includes $501 million and $447 million at September 30, 2012 and December 31, 2011, respectively, carried at fair value)	7,826		7,826		8,262
Derivative related liabilities					25
Other liabilities	24		24		47
Total liabilities	7,850		7,850		8,334
HSBC affiliates [Member]
Income/(Expense):
Interest income from HSBC affiliates	1	1	3	5
Interest expense paid to HSBC affiliates	(140)	(140)	(420)	(436)
Net interest income (loss)	(139)	(139)	(417)	(431)
Gain (loss) on FVO debt with affiliate	(35)	19	(54)	12
Servicing and other fees from HSBC affiliates:
Real estate secured servicing and related fees from HSBC Bank USA	3	2	8	8
Other servicing, processing, origination and support revenues	1	3	6	8
HSBC Technology and Services (USA) Inc. ("HTSU") administrative fees and rental revenue	4	(1)	12	1
Total servicing and other fees from HSBC affiliates	8	4	26	17
Support services from HSBC affiliates	(84)	(68)	(229)	(207)
Stock based compensation expense with HSBC	$ (2)	$ (2)	$ (6)	$ (6)