Related Party Transactions - Additional Information (Detail) (USD $)	3 Months Ended		9 Months Ended			3 Months Ended		9 Months Ended		3 Months Ended			9 Months Ended		12 Months Ended	24 Months Ended						9 Months Ended	12 Months Ended	3 Months Ended		9 Months Ended					9 Months Ended		9 Months Ended	12 Months Ended			3 Months Ended		9 Months Ended
	Sep. 30, 2012	Sep. 30, 2011	Sep. 30, 2012	Sep. 30, 2011	Dec. 31, 2011	Sep. 30, 2012 Series C Preferred Stock [Member]	Sep. 30, 2011 Series C Preferred Stock [Member]	Sep. 30, 2012 Series C Preferred Stock [Member]	Sep. 30, 2011 Series C Preferred Stock [Member]	Sep. 30, 2012 HSBC USA Inc [Member]	Mar. 31, 2012 HSBC USA Inc [Member]	Sep. 30, 2011 HSBC USA Inc [Member]	Sep. 30, 2012 HSBC USA Inc [Member]	Sep. 30, 2011 HSBC USA Inc [Member]	Dec. 31, 2011 HSBC USA Inc [Member] Y	Dec. 31, 2004 HSBC USA Inc [Member]	Jun. 30, 2012 HSBC USA Inc [Member]	Jan. 31, 2009 HSBC USA Inc [Member] GM and UP portfolios [Member]	Sep. 30, 2012 HSBC USA Inc [Member] Revolving Credit Facility [Member]	Dec. 31, 2011 HSBC USA Inc [Member] Commercial paper back-stop credit facility [Member]	Sep. 30, 2012 HSBC USA Inc [Member] Commercial Back Facility Maturity 2014 [Member]	Sep. 30, 2012 HSBC USA Inc [Member] Commercial Back Facility Maturity 2012 [Member]	Dec. 31, 2011 HSBC Bank USA Subsidiaries [Member]	Sep. 30, 2012 HSBC Global Resourcing UK Ltd [Member]	Sep. 30, 2011 HSBC Global Resourcing UK Ltd [Member]	Sep. 30, 2012 HSBC Global Resourcing UK Ltd [Member]	Sep. 30, 2011 HSBC Global Resourcing UK Ltd [Member]	Oct. 01, 2012 HSBC Investments [Member]	Mar. 31, 2012 HSBC Investments [Member]	Dec. 31, 2011 HSBC Investments [Member]	Sep. 30, 2012 HSBC Investments [Member] Commercial paper back-stop credit facility [Member]	Dec. 31, 2011 HSBC Investments [Member] Commercial paper back-stop credit facility [Member]	Sep. 30, 2012 HSBC North America [Member]	Dec. 31, 2010 HSBC North America [Member]	Dec. 31, 2011 HSBC North America [Member]	Jun. 30, 2011 HSBC North America [Member]	Dec. 31, 2010 HSBC North America [Member] Series C Preferred Stock [Member]	Dec. 31, 2010 HSBC North America [Member] Uncommitted Revolving Credit Facility [Member]	Sep. 30, 2012 HSBC Trinkaus & Burkhardt AG [Member] Commercial paper back-stop credit facility [Member]	Dec. 31, 2011 HSBC Trinkaus & Burkhardt AG [Member] Commercial paper back-stop credit facility [Member]	Dec. 31, 2010 HSBC Bank plc ("HBEU") [Member]
Related Party Transaction [Line Items]
Real estate secured receivables sold																$ 3,700,000,000
Receivables serviced for HSBC Bank USA										1,200,000,000			1,200,000,000		1,300,000,000
Payment of service fees										14,000,000		15,000,000	42,000,000	47,000,000
Borrowing capacity of credit facility															3,000,000,000				2,000,000,000	1,100,000,000	600,000,000	500,000,000						100,000,000				500,000,000						1,000,000,000		400,000,000
Expiration period															15
Line of Credit Facility Maximum Borrowing Capacity after Amendment																	4,000,000,000
Amounts outstanding on loan agreement										512,000,000			512,000,000
Expiration year													2017-09									2012-09
Uncommitted secured credit facility to subsidiaries										1,500,000,000			1,500,000,000		1,500,000,000
Outstanding balance										0			0		0
Outstanding principal balance																		12,400,000,000
Purchase account receivable related to credit card account relation													970,000,000
Intangible assets of discontinued credit card operations															29,000,000
Gain on sale of account relation											79,000,000
Gains on the daily sales of the receivables	55,000,000	274,000,000	1,659,000,000	598,000,000								145,000,000	89,000,000	407,000,000
Fees received for servicing receivable portfolios												153,000,000	207,000,000	458,000,000
Extended Amount													1,000,000,000										1,000,000,000
Support services from HSBC affiliates	84,000,000	68,000,000	229,000,000	207,000,000																				3,000,000	4,000,000	9,000,000	10,000,000
Notional values of derivative contracts	27,627,000,000		27,627,000,000		40,854,000,000					27,500,000,000,000			27,500,000,000,000		40,400,000,000,000
Fair value amount recognized for derivative instruments	183,000,000		183,000,000		584,000,000
Due to affiliate, carried at fair value	501,000,000		501,000,000		447,000,000
Gain (loss) on debt and related derivatives fair value										(35,000,000)		19,000,000	(54,000,000)	12,000,000
Loan agreements with affiliates																													250,000,000							600,000,000
First borrowing amount																																	200,000,000
Second borrowing amount																																	200,000,000
Third borrowing amount																																	200,000,000
Maturity year of long term debt			2035																														2034
Long-term debt	30,192,000,000		30,192,000,000		39,790,000,000																												600,000,000		600,000,000
Maturity year of line of credit																															2014-04								2012-12
Deposit																														500,000,000
Price of shares issued																																					1,000,000,000
Number of shares issued																																					1,000
Maturity period of line of credit																																		15 years
Dividend paid on preferred stock						21,000,000	21,000,000	64,000,000	68,000,000
Interest bearing deposits with banks	$ 1,363,000,000		$ 1,363,000,000		$ 1,140,000,000																																				$ 1,000,000,000