Fair Value Option - Components of Gain (Loss) on Instruments at Fair Value and Related Derivatives (Detail) - USD ($) $ in Millions	3 Months Ended
Mar. 31, 2025	Mar. 31, 2024
Components Of Gain On Instruments At Fair Value And Related Derivatives [Line Items]
Mark-to-market on related derivatives	$ (181)	$ 70
Gain (loss) on instruments designated at fair value and related derivatives	(3)	(20)
Gain (loss) on instruments designated at fair value and related derivatives
Components Of Gain On Instruments At Fair Value And Related Derivatives [Line Items]
Interest rate and other components	172	(118)
Credit risk component, total	(7)	1
Total mark-to-market on financial instruments designated at fair value	165	(117)
Mark-to-market on related derivatives	(169)	98
Net realized gain (loss) on related long-term debt derivatives	1	(1)
Gain (loss) on instruments designated at fair value and related derivatives	(3)	(20)
Gain (loss) on instruments designated at fair value and related derivatives \| Loans
Components Of Gain On Instruments At Fair Value And Related Derivatives [Line Items]
Interest rate and other components	0	0
Credit risk component, assets	(7)	1
Total mark-to-market on financial instruments designated at fair value	(7)	1
Mark-to-market on related derivatives	0	0
Net realized gain (loss) on related long-term debt derivatives	0	0
Gain (loss) on instruments designated at fair value and related derivatives	(7)	1
Gain (loss) on instruments designated at fair value and related derivatives \| Long-term debt
Components Of Gain On Instruments At Fair Value And Related Derivatives [Line Items]
Interest rate and other components	(16)	23
Credit risk component, liabilities	0	0
Total mark-to-market on financial instruments designated at fair value	(16)	23
Mark-to-market on related derivatives	17	(27)
Net realized gain (loss) on related long-term debt derivatives	1	(1)
Gain (loss) on instruments designated at fair value and related derivatives	2	(5)
Gain (loss) on instruments designated at fair value and related derivatives \| Hybrid Instruments
Components Of Gain On Instruments At Fair Value And Related Derivatives [Line Items]
Interest rate and other components	188	(141)
Credit risk component, liabilities	0	0
Total mark-to-market on financial instruments designated at fair value	188	(141)
Mark-to-market on related derivatives	(186)	125
Net realized gain (loss) on related long-term debt derivatives	0	0
Gain (loss) on instruments designated at fair value and related derivatives	$ 2	$ (16)

Components Of Gain On Instruments At Fair Value And Related Derivatives [Line Items]

No definition available.

Name:	hsbcusa_ComponentsOfGainOnInstrumentsAtFairValueAndRelatedDerivativesLineItems
Namespace Prefix:	hsbcusa_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Definition

Fair Value, Option, Credit Risk, Gains (Losses), Net

+ References

No definition available.

+ Details

Name:	hsbcusa_FairValueOptionCreditRiskGainsLossesNet
Namespace Prefix:	hsbcusa_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

Fair Value, Option, Interest Rate And Other Components, Gains (Losses)

+ References

No definition available.

+ Details

Name:	hsbcusa_FairValueOptionInterestRateAndOtherComponentsGainsLosses
Namespace Prefix:	hsbcusa_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

Fair value changes on fixed rate debt, loans and certain other financial instruments accounted for under fair value option as well as the fair value changes on the related derivatives and realized gains (losses) on the debt related derivatives.

+ References

No definition available.

+ Details

Name:	hsbcusa_GainLossOnInstrumentsDesignatedAtFairValueAndRelatedDerivative
Namespace Prefix:	hsbcusa_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

Net realized gain losses on the related long-term debt derivatives.

+ References

No definition available.

+ Details

Name:	hsbcusa_NetRealizedGainLossesOnRelatedLongTermDebtDerivatives
Namespace Prefix:	hsbcusa_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

Amount of realized and unrealized gain (loss) of derivative instruments not designated or qualifying as hedging instruments.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Name Accounting Standards Codification
-Topic 815
-SubTopic 10
-Section 50
-Paragraph 4C
-Subparagraph (e)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147480434/815-10-50-4C

Reference 2: http://www.xbrl.org/2009/role/commonPracticeRef
-Name Accounting Standards Codification
-Section 50
-Paragraph 4CC
-SubTopic 10
-Topic 815
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147480434/815-10-50-4CC

+ Details

Name:	us-gaap_DerivativeInstrumentsNotDesignatedAsHedgingInstrumentsGainLossNet
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

For each line item in the statement of financial position, the amounts of gains and losses from fair value changes included in earnings.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Name Accounting Standards Codification
-Topic 825
-SubTopic 10
-Section 50
-Paragraph 30
-Subparagraph (a)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147482907/825-10-50-30

+ Details

Name:	us-gaap_FairValueOptionChangesInFairValueGainLoss1
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

This item represents the estimated amount of gains or losses included in earnings during the period attributable to changes in instrument-specific credit risk arising from loans and other receivables held as assets.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Name Accounting Standards Codification
-Topic 825
-SubTopic 10
-Section 50
-Paragraph 30
-Subparagraph (c)(1)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147482907/825-10-50-30

+ Details

Name:	us-gaap_FairValueOptionCreditRiskGainsLossesOnAssets
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

Amount, before tax, after reclassification adjustment, of gain (loss) from increase (decrease) in instrument-specific credit risk of financial liability measured under fair value option.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Topic 944
-SubTopic 220
-Name Accounting Standards Codification
-Section S99
-Paragraph 1
-Subparagraph (SX 210.7-04(19))
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147477250/944-220-S99-1

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Topic 220
-SubTopic 10
-Name Accounting Standards Codification
-Section 45
-Paragraph 11
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147482790/220-10-45-11

Reference 3: http://www.xbrl.org/2003/role/disclosureRef
-Topic 220
-SubTopic 10
-Name Accounting Standards Codification
-Section 45
-Paragraph 10A
-Subparagraph (l)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147482790/220-10-45-10A

+ Details

Name:	us-gaap_OtherComprehensiveIncomeLossFinancialLiabilityFairValueOptionBeforeTaxAfterReclassificationAdjustment
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Details

Name:	us-gaap_IncomeStatementLocationAxis=hsbcusa_GainlossonInstrumentsDesignatedatFairValueandRelatedDerivativesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

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

- Details

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

- Details

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