Allowance for Credit Losses - Updates to Economic Scenarios (Details) $ in Millions	Mar. 31, 2020 scenario	Jan. 01, 2020 USD ($)
Measurement of ECL Measurements [Line Items]
Number of COVID-19 economic scenarios \| scenario	3
Management judgment allowance for risk factors associated with large loan exposure in our commercial loan portfolio \| $		$ 125

Allowance for Credit Losses, Management Judgment Allowance for Risk Factors

No definition available.

Name:	hsbcusa_AllowanceforCreditLossesManagementJudgmentAllowanceforRiskFactors
Namespace Prefix:	hsbcusa_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant