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Retained Earnings and Regulatory Capital Requirements - Additional Information (Details) (USD $)
In Millions, unless otherwise specified
 12 Months Ended
Dec. 31, 2014
Dec. 31, 2013
Dec. 31, 2012
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items]      
Deferred Tax Assets Excluded In Computation Of Regulatory Capital $ 8hsbcusa_DeferredTaxAssetsExcludedInComputationOfRegulatoryCapital $ 897hsbcusa_DeferredTaxAssetsExcludedInComputationOfRegulatoryCapital  
Contributions 0us-gaap_ProceedsFromContributionsFromParent 0us-gaap_ProceedsFromContributionsFromParent 312us-gaap_ProceedsFromContributionsFromParent
Distributions 0hsbcusa_PaymentsForDistributionsToSubsidiary    
HSBC North America Inc. HNAI [Member]      
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items]      
Contributions $ 0us-gaap_ProceedsFromContributionsFromParent
/ dei_LegalEntityAxis
= hsbcusa_HNAIMember