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Loans - Delinquency Ratio for Consumer Loan - Additional Information (Detail) (USD $)
In Millions, unless otherwise specified
Mar. 31, 2015
Dec. 31, 2014
Financing Receivable, Recorded Investment [Line Items]    
Residential Mortgage Loan Delinquency Carried At Lower Of Amortized Cost Or Fair Value Less Cost To Sell $ 908hsbcusa_ResidentialMortgageLoanDelinquencyCarriedAtLowerOfAmortizedCostOrFairValueLessCostToSell $ 936hsbcusa_ResidentialMortgageLoanDelinquencyCarriedAtLowerOfAmortizedCostOrFairValueLessCostToSell
Consumer Loans [Member]    
Financing Receivable, Recorded Investment [Line Items]    
Mortgage Loans in Process of Foreclosure, Amount $ 609hsbcusa_MortgageLoansinProcessofForeclosureAmount
/ us-gaap_FinancialInstrumentAxis
= us-gaap_ConsumerLoanMember		 $ 608hsbcusa_MortgageLoansinProcessofForeclosureAmount
/ us-gaap_FinancialInstrumentAxis
= us-gaap_ConsumerLoanMember