Loans Receivable, Commercial Loans Removed from TDR Classification

No definition available.

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Namespace Prefix:	hsbcusa_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

Loans and Leases Receivable, Unamortized Premium (Discount), Net

+ References

No definition available.

+ Details

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

- Definition

Net Deferred Origination Costs (Fees)

+ References

No definition available.

+ Details

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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

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Data Type:	xbrli:stringItemType
Balance Type:	na
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- Definition

Amount, after troubled debt restructuring, of modified financing receivable.

+ References

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 10
-Section 50
-Paragraph 33
-URI http://asc.fasb.org/extlink&oid=118936363&loc=SL6953676-111524

+ Details

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

- Definition

Amount of financing receivable modified as troubled debt restructuring within previous 12 months, with subsequent payment default.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 10
-Section 50
-Paragraph 34
-Subparagraph (a)(2)
-URI http://asc.fasb.org/extlink&oid=118936363&loc=SL6953682-111524

+ Details

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Period Type:	duration

- Details

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Namespace Prefix:
Data Type:	na
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Period Type:

- Details

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

Loans - Additional Information (Detail) - USD ($)	3 Months Ended			9 Months Ended
Loans - Additional Information (Detail) - USD ($)	Sep. 30, 2019	Jun. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018	Dec. 31, 2018
Accounts, Notes, Loans and Financing Receivable [Line Items]
Net deferred origination costs (fees)	$ 79,000,000			$ 79,000,000		$ 77,000,000
Net unamortized premium (discount)	2,000,000			2,000,000		$ 11,000,000
Commercial loans removed from TDR classification		$ 12,000,000			$ 0
Commercial Loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Financing Receivable, Troubled Debt Restructuring, Postmodification	0		$ 0	0	0
Financing Receivable, Troubled Debt Restructuring, Subsequent Default	0		0	0	0
Consumer Loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Financing Receivable, Troubled Debt Restructuring, Postmodification	3,000,000		7,000,000	6,000,000	29,000,000
Financing Receivable, Troubled Debt Restructuring, Subsequent Default	$ 0		$ 4,000,000	$ 3,000,000	$ 8,000,000