Litigation and Regulatory Matters - Additional Information (Detail) (USD $)	3 Months Ended	9 Months Ended				9 Months Ended					1 Months Ended			1 Months Ended	9 Months Ended		36 Months Ended
	Sep. 30, 2012	Sep. 30, 2012	Sep. 30, 2012 Madoff Litigation [Member]	Feb. 09, 2012 Foreclosure Practices [Member] Services State	Dec. 31, 2011 Foreclosure Practices [Member] HSBC North America Inc. [Member]	Sep. 30, 2012 Foreclosure Practices [Member] Minimum [Member]	Sep. 30, 2012 Foreclosure Practices [Member] Maximum [Member]	Sep. 30, 2012 Residential Mortgage Backed Securities Related Litigation [Member] Institution Officers	Feb. 21, 2012 Residential Mortgage Backed Securities Related Litigation [Member]	Jan. 31, 2012 Residential Mortgage Backed Securities Related Litigation [Member]	Jan. 31, 2012 Residential Mortgage Backed Securities Related Litigation [Member] Sealink [Member] Defendant	Sep. 30, 2012 Residential Mortgage Backed Securities Related Litigation [Member] HSH Nordbank AG [Member]	Sep. 30, 2012 Residential Mortgage Backed Securities Related Litigation [Member] HSBC Securities [Member]	May 31, 2011 Knox Family Trust Litigation [Member] Proceedings	Sep. 30, 2012 Knox Family Trust Litigation [Member] Proceedings LegalMatter	Sep. 30, 2012 AML/BSA Related Litigation [Member]	Dec. 31, 2007 Mortgage Securitization Activity Related Litigation [Member] HSBC Securities [Member]	Sep. 30, 2012 Mortgage Securitization Activity Related Litigation [Member] HSBC Securities [Member]	Dec. 31, 2011 Mortgage Securitization Activity Related Litigation [Member] HSBC Securities [Member]
Loss Contingencies [Line Items]
Damages and additional recoveries sought			$ 9,000,000,000
Number of proceedings awarded for plaintiffs															7
Total damages															26,000,000
Amount of final judgments														25,000,000
Number of proceedings entered by court														2
Number of proceedings agreed by HSBC Bank USA														3
Number of matters remitted to the Surrogate court by Appellate Division															3
Number of days within which to seek permission to appeal															30 days
Loss contingency claims settled and dismissed number other														2
Proceedings agreed by HSBC Bank USA on appeal														1
Loan modification or a lump sum payment						500	125,000
Number of states under different departments				49
Accrual portion of HSBC North					38,000,000
Number of U.S. mortgage servicers with which settlement is announced				5
Expense accrual related to certain regulatory matters	800,000,000	1,500,000,000														1,500,000,000
Loans sold to HIS																	24,000,000,000
Outstanding principal balance on loan																		7,700,000,000	8,500,000,000
Unpaid principal balance of securities													1,800,000,000
Number of financial institutions								17
Number of former and current officers and directors								5
Amount of allegation against bank										122,400,000
Amount of Allegation against company											$ 948,800,000	$ 41,300,000
Loss Contingency, Number of Defendants											49
Number of defendants discontinued											43,000,000
Time Period to Serve Defendants									120 days