Allowance for Credit Losses - Summary of Changes in Allowance for Credit Losses and Related Loan Balance by Product (Detail) - USD ($) $ in Millions	12 Months Ended
Dec. 31, 2025	Dec. 31, 2024	Dec. 31, 2023
Allowance for Loan and Lease Losses [Roll Forward]
Allowance for credit losses - beginning of period	$ 537	$ 591	$ 584
Provision charged (credited) to income	67	22	51
Charge-offs	(177)	(87)	(62)
Recoveries	15	11	18
Net (charge-offs) recoveries	(162)	(76)	(44)
Allowance for credit losses - end of period	442	537	591
Commercial loans
Allowance for Loan and Lease Losses [Roll Forward]
Charge-offs	(168)	(78)	(48)
Commercial loans \| Real estate, including construction
Allowance for Loan and Lease Losses [Roll Forward]
Allowance for credit losses - beginning of period	144	144	200
Provision charged (credited) to income	38	17	(56)
Charge-offs	(64)	(17)	0
Recoveries	2	0	0
Net (charge-offs) recoveries	(62)	(17)	0
Allowance for credit losses - end of period	120	144	144
Commercial loans \| Business and corporate banking
Allowance for Loan and Lease Losses [Roll Forward]
Allowance for credit losses - beginning of period	381	429	350
Provision charged (credited) to income	34	11	118
Charge-offs	(104)	(61)	(48)
Recoveries	4	2	9
Net (charge-offs) recoveries	(100)	(59)	(39)
Allowance for credit losses - end of period	315	381	429
Commercial loans \| Other commercial
Allowance for Loan and Lease Losses [Roll Forward]
Allowance for credit losses - beginning of period	1	1	1
Provision charged (credited) to income	0	0	0
Charge-offs	0	0	0
Recoveries	0	0	0
Net (charge-offs) recoveries	0	0	0
Allowance for credit losses - end of period	1	1	1
Consumer loans \| Residential Mortgages
Allowance for Loan and Lease Losses [Roll Forward]
Allowance for credit losses - beginning of period	(12)	(9)	11
Provision charged (credited) to income	(4)	(7)	(19)
Charge-offs	(1)	0	(4)
Recoveries	5	4	3
Net (charge-offs) recoveries	4	4	(1)
Allowance for credit losses - end of period	(12)	(12)	(9)
Consumer loans \| Other consumer
Allowance for Loan and Lease Losses [Roll Forward]
Allowance for credit losses - beginning of period	23	26	22
Provision charged (credited) to income	(1)	1	8
Charge-offs	(8)	(9)	(10)
Recoveries	4	5	6
Net (charge-offs) recoveries	(4)	(4)	(4)
Allowance for credit losses - end of period	$ 18	$ 23	$ 26

A roll forward is a reconciliation of a concept from the beginning of a period to the end of a period.

No definition available.

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

- Definition

Amount excluding accrued interest, of allowance for credit loss on financing receivable. Excludes net investment in lease.

+ References

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Topic 326
-SubTopic 20
-Name Accounting Standards Codification
-Section 45
-Paragraph 1
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147479344/326-20-45-1

+ Details

Name:	us-gaap_FinancingReceivableAllowanceForCreditLossExcludingAccruedInterest
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Amount, excluding accrued interest, of increase in allowance for credit loss on financing receivable from recovery. Excludes net investment in lease.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Topic 326
-SubTopic 20
-Name Accounting Standards Codification
-Section 50
-Paragraph 13
-Subparagraph (e)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147479319/326-20-50-13

+ Details

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

- Definition

Amount, excluding accrued interest, of decrease in allowance for credit loss on financing receivable from writeoff. Excludes net investment in lease.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Topic 326
-SubTopic 20
-Name Accounting Standards Codification
-Section 50
-Paragraph 13
-Subparagraph (d)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147479319/326-20-50-13

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Topic 326
-SubTopic 20
-Name Accounting Standards Codification
-Section 50
-Paragraph 6
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147479319/326-20-50-6

+ Details

Name:	us-gaap_FinancingReceivableExcludingAccruedInterestAllowanceForCreditLossWriteoff
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

Amount, excluding accrued interest, of decrease (increase) in allowance for credit loss on financing receivable from writeoff (recovery). Excludes net investment in lease.

+ References

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Topic 326
-SubTopic 20
-Name Accounting Standards Codification
-Section 50
-Paragraph 13
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147479319/326-20-50-13

+ Details

Name:	us-gaap_FinancingReceivableExcludingAccruedInterestAllowanceForCreditLossWriteoffAfterRecovery
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

Amount, excluding accrued interest, of credit loss expense (reversal of expense) on financing receivable. Excludes net investment in lease.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Topic 326
-SubTopic 20
-Name Accounting Standards Codification
-Section 50
-Paragraph 13
-Subparagraph (b)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147479319/326-20-50-13

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Topic 220
-SubTopic 40
-Name Accounting Standards Codification
-Section 50
-Paragraph 22
-Subparagraph (a)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147476148/220-40-50-22

+ Details

Name:	us-gaap_FinancingReceivableExcludingAccruedInterestCreditLossExpenseReversal
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Details

Name:	us-gaap_FinancingReceivablePortfolioSegmentAxis=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_OtherCommercialMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

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

- Details

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

- Details

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