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Income Taxes - Additional Information (Details) (USD $)
In Millions, unless otherwise specified
Dec. 31, 2014
Dec. 31, 2013
Dec. 31, 2012
Jun. 30, 2014
Income Tax Contingency [Line Items]        
Unrecognized tax benefit, affect the effective tax rate $ 11us-gaap_UnrecognizedTaxBenefitsThatWouldImpactEffectiveTaxRate $ 334us-gaap_UnrecognizedTaxBenefitsThatWouldImpactEffectiveTaxRate $ 314us-gaap_UnrecognizedTaxBenefitsThatWouldImpactEffectiveTaxRate  
Accruals for payment of interest and penalties associated with uncertain tax positions 3us-gaap_IncomeTaxExaminationPenaltiesAndInterestAccrued 208us-gaap_IncomeTaxExaminationPenaltiesAndInterestAccrued 159us-gaap_IncomeTaxExaminationPenaltiesAndInterestAccrued  
Increase in accruals for payment of interest and penalties associated with uncertain tax positions (205)hsbcusa_UnrecognizedTaxBenefitsIncreaseDecreaseInIncomeTaxPenaltiesAndInterestAccrued 49hsbcusa_UnrecognizedTaxBenefitsIncreaseDecreaseInIncomeTaxPenaltiesAndInterestAccrued    
Net deferred tax asset 1,353us-gaap_DeferredTaxAssetsLiabilitiesNet 1,557us-gaap_DeferredTaxAssetsLiabilitiesNet    
Income, Taxes and Other Liabilities - Income Tax Reserve [Member]        
Income Tax Contingency [Line Items]        
Income Tax Examination, Increase (Decrease) in Liability from Prior Year       183us-gaap_IncomeTaxExaminationIncreaseDecreaseInLiabilityFromPriorYear
/ us-gaap_BalanceSheetLocationAxis
= hsbcusa_IncomeTaxesandOtherLiabilitiesIncomeTaxReserveMember
Interest, Taxes and Other Liabilities - Accrued Interest [Member]        
Income Tax Contingency [Line Items]        
Income Tax Examination, Increase (Decrease) in Liability from Prior Year       $ 120us-gaap_IncomeTaxExaminationIncreaseDecreaseInLiabilityFromPriorYear
/ us-gaap_BalanceSheetLocationAxis
= hsbcusa_InterestTaxesandOtherLiabilitiesAccruedInterestMember