Loans - Contractual Maturity of Loans Outstanding by Repricing Characteristic (Details) $ in Millions	Dec. 31, 2021 USD ($)
Accounts, Notes, Loans and Financing Receivable [Line Items]
Receivables at Predetermined Interest Rates	$ 6,390
Receivables at Floating or Adjustable Rates	25,658
Total Loans Due After One Year	32,048
Commercial loans: \| Real Estate, including Construction
Accounts, Notes, Loans and Financing Receivable [Line Items]
Receivables at Predetermined Interest Rates	240
Receivables at Floating or Adjustable Rates	3,151
Total Loans Due After One Year	3,391
Commercial loans: \| Business and corporate banking
Accounts, Notes, Loans and Financing Receivable [Line Items]
Receivables at Predetermined Interest Rates	407
Receivables at Floating or Adjustable Rates	5,340
Total Loans Due After One Year	5,747
Commercial loans: \| Global banking
Accounts, Notes, Loans and Financing Receivable [Line Items]
Receivables at Predetermined Interest Rates	324
Receivables at Floating or Adjustable Rates	4,250
Total Loans Due After One Year	4,574
Commercial loans: \| Other commercial
Accounts, Notes, Loans and Financing Receivable [Line Items]
Receivables at Predetermined Interest Rates	189
Receivables at Floating or Adjustable Rates	2,485
Total Loans Due After One Year	2,674
Consumer loans: \| Residential mortgages
Accounts, Notes, Loans and Financing Receivable [Line Items]
Receivables at Predetermined Interest Rates	5,181
Receivables at Floating or Adjustable Rates	10,065
Total Loans Due After One Year	15,246
Consumer loans: \| Home equity mortgages
Accounts, Notes, Loans and Financing Receivable [Line Items]
Receivables at Predetermined Interest Rates	23
Receivables at Floating or Adjustable Rates	184
Total Loans Due After One Year	207
Consumer loans: \| Credit cards
Accounts, Notes, Loans and Financing Receivable [Line Items]
Receivables at Predetermined Interest Rates	26
Receivables at Floating or Adjustable Rates	178
Total Loans Due After One Year	204
Consumer loans: \| Other consumer
Accounts, Notes, Loans and Financing Receivable [Line Items]
Receivables at Predetermined Interest Rates	0
Receivables at Floating or Adjustable Rates	5
Total Loans Due After One Year	$ 5

Financing Receivable, Before Allowance For Credit Loss, Maturity, Due After One Year

No definition available.

Name:	hsbcusa_FinancingReceivableBeforeAllowanceForCreditLossMaturityDueAfterOneYear
Namespace Prefix:	hsbcusa_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

+ References

No definition available.

+ Details

Name:	us-gaap_AccountsNotesAndLoansReceivableLineItems
Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Definition

Amount, before allowance for credit loss, of financing receivable with adjustable interest rate, maturing after next fiscal year following current fiscal year. Excludes interim and annual periods when interim periods are reported from current statement of financial position date (rolling approach).

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher SEC
-Name Regulation S-K (SK)
-Number 229
-Section 1404
-Paragraph (b)
-Subparagraph (2)

+ Details

Name:	us-gaap_FinancingReceivableBeforeAllowanceForCreditLossAdjustableInterestRateMaturityAfterYearOne
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Amount, before allowance for credit loss, of financing receivable with predetermined interest rate, maturing after next fiscal year following current fiscal year. Excludes floating and adjustable rates and interim and annual periods when interim periods are reported from current statement of financial position date (rolling approach).

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher SEC
-Name Regulation S-K (SK)
-Number 229
-Section 1404
-Paragraph (b)
-Subparagraph (1)

+ Details

Name:	us-gaap_FinancingReceivableBeforeAllowanceForCreditLossPredeterminedInterestRateMaturityAfterYearOne
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Details

Name:	us-gaap_FinancialInstrumentAxis=us-gaap_CommercialLoanMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis=us-gaap_CommercialRealEstatePortfolioSegmentMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis=hsbcusa_BusinessandCorporateBankingMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis=hsbcusa_GlobalBankingMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis=hsbcusa_OtherCommercialMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FinancialInstrumentAxis=us-gaap_ConsumerLoanMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis=us-gaap_ResidentialMortgageMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis=us-gaap_HomeEquityMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis=us-gaap_CreditCardReceivablesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis=us-gaap_ConsumerPortfolioSegmentMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type: