Credit card receivable balance associated with account relationships purchased.

No definition available.

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

- Definition

Fair value of Intangible asset related to account relationships purchased include in branch sale.

+ References

No definition available.

+ Details

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

- Definition

Fair value of Intangible asset related to account relationships purchased retained.

+ References

No definition available.

+ Details

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

- Definition

Fair value of intangible related to asset account relationships purchased.

+ References

No definition available.

+ Details

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

- Definition

Outstanding Principal Balances At Period End Of Residential Mortgage Loans Owned and Serviced For Others

+ References

No definition available.

+ Details

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

- Definition

Outstanding principal balances at period end.

+ References

No definition available.

+ Details

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

- Details

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

- Definition

Useful life of finite-lived intangible assets, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

+ References

No definition available.

+ Details

Name:	us-gaap_FiniteLivedIntangibleAssetUsefulLife
Namespace Prefix:	us-gaap_
Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	duration

- Definition

Amount of gain (loss) on sale or disposal of intangible assets.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 230

-SubTopic 10

-Section 45

-Paragraph 28

-URI http://asc.fasb.org/extlink&oid=31042434&loc=d3e3602-108585

Reference 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 225

-SubTopic 10

-Section S99

-Paragraph 2

-Subparagraph (SX 210.5-03.7,9)

-URI http://asc.fasb.org/extlink&oid=26872669&loc=d3e20235-122688

+ Details

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

- Definition

The cash inflow from disposal of asset without physical form usually arising from contractual or other legal rights, excluding goodwill.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Glossary Investing Activities

-URI http://asc.fasb.org/extlink&oid=6516133

Reference 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 230

-SubTopic 10

-Section 45

-Paragraph 12

-Subparagraph (c)

-URI http://asc.fasb.org/extlink&oid=31042434&loc=d3e3179-108585

+ Details

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

- Definition

Amount of revenue from servicing real estate mortgages, credit cards, and other financial assets held by others. Includes premiums received in lieu of regular servicing fees.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher SEC

-Name Regulation S-X (SX)

-Number 210

-Section 04

-Paragraph 13

-Article 9

Reference 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 942

-SubTopic 225

-Section S99

-Paragraph 1

-Subparagraph (SX 210.9-04.13 (d))

-URI http://asc.fasb.org/extlink&oid=6879574&loc=d3e536633-122882

+ Details

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

Intangible Assets - Additional Information (Detail) (USD $) In Millions, unless otherwise specified				3 Months Ended		9 Months Ended		1 Months Ended	3 Months Ended
	Sep. 30, 2014	Dec. 31, 2013	Mar. 31, 2012	Sep. 30, 2014 Residential mortgage banking revenue [Member]	Sep. 30, 2013 Residential mortgage banking revenue [Member]	Sep. 30, 2014 Residential mortgage banking revenue [Member]	Sep. 30, 2013 Residential mortgage banking revenue [Member]	Mar. 31, 2012 Purchased credit card relationships [Member]	Sep. 30, 2014 Commercial [Member] Mortgage servicing rights [Member]
Finite-Lived Intangible Assets [Line Items]
Outstanding principal balances at period end of residential mortgage loans serviced for others	$ 24,048	$ 26,951
Servicing fees collected				17	20	52	62
Outstanding principal balances at period end of residential mortgage loans owned and serviced for others	41,638	44,039
Proceeds from sale of Commercial MSRs									22
Gain on sale of Commercial MSRs									16
Purchased from HSBC Finance account of credit card			746
Credit card receivables not being sold to Capital One at a fair value			108
Fair value of Intangible asset related to account relationships purchased include in branch sale			43
Fair value of Intangible asset related to account relationships purchased retained			$ 65
Useful life								10 years