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Guarantee Arrangements and Pledged Assets and Collateral - Outstanding Repurchase Demands Received From GSEs and Other Third Parties (Detail) (Obligation to Repurchase Receivables Sold [Member], USD $)
In Millions, unless otherwise specified
Mar. 31, 2015
Dec. 31, 2014
Loss Contingencies [Line Items]    
Outstanding repurchase demands received $ 3hsbcusa_OutstandingRepurchaseDemands $ 3hsbcusa_OutstandingRepurchaseDemands
GSEs [Member]    
Loss Contingencies [Line Items]    
Outstanding repurchase demands received 2hsbcusa_OutstandingRepurchaseDemands
/ us-gaap_CounterpartyNameAxis
= hsbcusa_GovernmentSponsoredEntitiesMember
/ us-gaap_LossContingenciesByNatureOfContingencyAxis
= us-gaap_ObligationToRepurchaseReceivablesSoldMember		 2hsbcusa_OutstandingRepurchaseDemands
/ us-gaap_CounterpartyNameAxis
= hsbcusa_GovernmentSponsoredEntitiesMember
/ us-gaap_LossContingenciesByNatureOfContingencyAxis
= us-gaap_ObligationToRepurchaseReceivablesSoldMember
Others [Member]    
Loss Contingencies [Line Items]    
Outstanding repurchase demands received $ 1hsbcusa_OutstandingRepurchaseDemands
/ us-gaap_CounterpartyNameAxis
= hsbcusa_OthersMember
/ us-gaap_LossContingenciesByNatureOfContingencyAxis
= us-gaap_ObligationToRepurchaseReceivablesSoldMember		 $ 1hsbcusa_OutstandingRepurchaseDemands
/ us-gaap_CounterpartyNameAxis
= hsbcusa_OthersMember
/ us-gaap_LossContingenciesByNatureOfContingencyAxis
= us-gaap_ObligationToRepurchaseReceivablesSoldMember