Fair Value Option - Summary of Fair Value and Unpaid Principal Balance (Details) (USD $) In Millions, unless otherwise specified	Mar. 31, 2015	Dec. 31, 2014
Loans Receivable [Member]
Fair Value, Option, Quantitative Disclosures [Line Items]
Commercial loans held for sale, Fair Value	$ 255	$ 384
Commercial loans held for sale, Unpaid Principal Balance	270	390
Long-term debt [Member]
Fair Value, Option, Quantitative Disclosures [Line Items]
Fixed rate long-term debt, Fair Value	2,191	2,179
Fixed rate long-term debt, Unpaid Principal Balance	1,750	1,750
Hybrid instruments, Fair Value	6,842	6,612
Hybrid Instruments, Unpaid Principal Balance	6,466	6,275
Deposits [Member]
Fair Value, Option, Quantitative Disclosures [Line Items]
Hybrid instruments, Fair Value	6,948	7,346
Hybrid Instruments, Unpaid Principal Balance	$ 6,768	$ 7,176

Fixed-rate debt accounted for under fair value option.

No definition available.

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- Definition

Unpaid Principal Balance Commercial Syndicated Loans Held For Sale Carried at Fair Value

+ References

No definition available.

+ Details

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Period Type:	instant

- Definition

Unpaid principal balance on fixed-rate debt accounted for under FVO.

+ References

No definition available.

+ Details

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Namespace Prefix:	hsbcusa_
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Balance Type:	credit
Period Type:	instant

- Definition

Unpaid Principal Balance On Hybrid Instruments at Fair Value Option

+ References

No definition available.

+ Details

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- Details

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Period Type:	duration

- Definition

Fair value as of the balance sheet date of hybrid instruments.

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 825

-SubTopic 10

-Section 50

-Paragraph 10

-Subparagraph (a)

-URI http://asc.fasb.org/extlink&oid=35750535&loc=d3e13433-108611

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 825

-SubTopic 10

-Section 50

-Paragraph 15

-URI http://asc.fasb.org/extlink&oid=35750535&loc=d3e13495-108611

Reference 3: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 815

-SubTopic 15

-Section 45

-Paragraph 1

-URI http://asc.fasb.org/extlink&oid=6437212&loc=d3e50806-113969

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Balance Type:	debit
Period Type:	instant

- Definition

Fair value portion of loans held-for-sale including, but not limited to, mortgage loans and finance receivables.

+ References

No definition available.

+ Details

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- Details

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- Details

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