Fair Value Measurements - Carrying Value and Estimated Fair Value of Financial Instruments (Detail) (USD $) In Millions, unless otherwise specified	Mar. 31, 2015	Dec. 31, 2014
Fair Value Of Other Financial Instrument [Line Items]
Derivatives	$ 8,403us-gaap_DerivativeAssets	$ 7,258us-gaap_DerivativeAssets
Derivatives	11,846us-gaap_DerivativeLiabilities	8,413us-gaap_DerivativeLiabilities
Level 1 [Member]
Fair Value Of Other Financial Instrument [Line Items]
Short-term financial assets	972	891
Federal funds sold and securities purchased under resale agreements	0	0
Non-derivative trading assets	2,912	2,675
Derivatives	8	10
Securities	25,141	22,048
Commercial loans, net of allowance for credit losses	0	0
Consumer loans, net of allowance for credit losses	0	0
Short-term financial liabilities	0	0
Deposits designated under fair value option	0	0
Non-derivative trading liabilities	477	653
Derivatives	19	8
Long-term debt	0	0
Long-term debt designated under fair value option	0	0
Level 1 [Member] \| Commercial Loans [Member]
Fair Value Of Other Financial Instrument [Line Items]
Commercial loans designated under fair value option and held for sale	0	0
Loans held for sale	0	0
Level 1 [Member] \| Consumer Loans [Member] \| Residential Mortgage [Member]
Fair Value Of Other Financial Instrument [Line Items]
Loans held for sale	0	0
Level 1 [Member] \| Consumer Loans [Member] \| Other consumer [Member]
Fair Value Of Other Financial Instrument [Line Items]
Loans held for sale	0	0
Level 1 [Member] \| Deposits Without Fixed Maturities [Member]
Fair Value Of Other Financial Instrument [Line Items]
Deposits	0	0
Level 1 [Member] \| Deposits With Fixed Maturities [Member]
Fair Value Of Other Financial Instrument [Line Items]
Deposits	0	0
Level 2 [Member]
Fair Value Of Other Financial Instrument [Line Items]
Short-term financial assets	32,249	30,807
Federal funds sold and securities purchased under resale agreements	6,965	1,413
Non-derivative trading assets	9,925	9,722
Derivatives	8,350	7,200
Securities	22,305	21,787
Commercial loans, net of allowance for credit losses	0	0
Consumer loans, net of allowance for credit losses	0	0
Short-term financial liabilities	15,671	12,813
Deposits designated under fair value option	5,022	5,378
Non-derivative trading liabilities	169	52
Derivatives	11,798	8,376
Long-term debt	21,259	19,524
Long-term debt designated under fair value option	8,391	8,144
Level 2 [Member] \| Commercial Loans [Member]
Fair Value Of Other Financial Instrument [Line Items]
Commercial loans designated under fair value option and held for sale	255	384
Loans held for sale	36	144
Level 2 [Member] \| Consumer Loans [Member] \| Residential Mortgage [Member]
Fair Value Of Other Financial Instrument [Line Items]
Loans held for sale	20	14
Level 2 [Member] \| Consumer Loans [Member] \| Other consumer [Member]
Fair Value Of Other Financial Instrument [Line Items]
Loans held for sale	0	0
Level 2 [Member] \| Deposits Without Fixed Maturities [Member]
Fair Value Of Other Financial Instrument [Line Items]
Deposits	109,625	105,962
Level 2 [Member] \| Deposits With Fixed Maturities [Member]
Fair Value Of Other Financial Instrument [Line Items]
Deposits	2,524	2,813
Level 3 [Member]
Fair Value Of Other Financial Instrument [Line Items]
Short-term financial assets	39	48
Federal funds sold and securities purchased under resale agreements	0	0
Non-derivative trading assets	3,101	3,093
Derivatives	45	48
Securities	0	0
Commercial loans, net of allowance for credit losses	62,494	58,891
Consumer loans, net of allowance for credit losses	18,143	17,896
Short-term financial liabilities	39	48
Deposits designated under fair value option	1,926	1,968
Non-derivative trading liabilities	0	0
Derivatives	29	29
Long-term debt	0	0
Long-term debt designated under fair value option	642	647
Level 3 [Member] \| Commercial Loans [Member]
Fair Value Of Other Financial Instrument [Line Items]
Commercial loans designated under fair value option and held for sale	0	0
Loans held for sale	0	0
Level 3 [Member] \| Consumer Loans [Member] \| Residential Mortgage [Member]
Fair Value Of Other Financial Instrument [Line Items]
Loans held for sale	5	5
Level 3 [Member] \| Consumer Loans [Member] \| Other consumer [Member]
Fair Value Of Other Financial Instrument [Line Items]
Loans held for sale	90	66
Level 3 [Member] \| Deposits Without Fixed Maturities [Member]
Fair Value Of Other Financial Instrument [Line Items]
Deposits	0	0
Level 3 [Member] \| Deposits With Fixed Maturities [Member]
Fair Value Of Other Financial Instrument [Line Items]
Deposits	0	0
Carrying Value [Member]
Fair Value Of Other Financial Instrument [Line Items]
Short-term financial assets	33,260	31,746
Federal funds sold and securities purchased under resale agreements	6,965	1,413
Non-derivative trading assets	15,938	15,490
Derivatives	8,403	7,258
Securities	47,111	43,609
Commercial loans, net of allowance for credit losses	61,113	57,595
Consumer loans, net of allowance for credit losses	19,642	19,466
Short-term financial liabilities	15,710	12,861
Deposits designated under fair value option	6,948	7,346
Non-derivative trading liabilities	646	705
Derivatives	11,846	8,413
Long-term debt	20,387	18,733
Long-term debt designated under fair value option	9,033	8,791
Carrying Value [Member] \| Commercial Loans [Member]
Fair Value Of Other Financial Instrument [Line Items]
Commercial loans designated under fair value option and held for sale	255	384
Loans held for sale	36	144
Carrying Value [Member] \| Consumer Loans [Member] \| Residential Mortgage [Member]
Fair Value Of Other Financial Instrument [Line Items]
Loans held for sale	24	18
Carrying Value [Member] \| Consumer Loans [Member] \| Other consumer [Member]
Fair Value Of Other Financial Instrument [Line Items]
Loans held for sale	90	66
Carrying Value [Member] \| Deposits Without Fixed Maturities [Member]
Fair Value Of Other Financial Instrument [Line Items]
Deposits	109,625	105,962
Carrying Value [Member] \| Deposits With Fixed Maturities [Member]
Fair Value Of Other Financial Instrument [Line Items]
Deposits	2,521	2,810
Estimate of fair value [Member]
Fair Value Of Other Financial Instrument [Line Items]
Short-term financial assets	33,260	31,746
Federal funds sold and securities purchased under resale agreements	6,965	1,413
Non-derivative trading assets	15,938	15,490
Derivatives	8,403	7,258
Securities	47,446	43,835
Commercial loans, net of allowance for credit losses	62,494	58,891
Consumer loans, net of allowance for credit losses	18,143	17,896
Short-term financial liabilities	15,710	12,861
Deposits designated under fair value option	6,948	7,346
Non-derivative trading liabilities	646	705
Derivatives	11,846	8,413
Long-term debt	21,259	19,524
Long-term debt designated under fair value option	9,033	8,791
Estimate of fair value [Member] \| Commercial Loans [Member]
Fair Value Of Other Financial Instrument [Line Items]
Commercial loans designated under fair value option and held for sale	255	384
Loans held for sale	36	144
Estimate of fair value [Member] \| Consumer Loans [Member] \| Residential Mortgage [Member]
Fair Value Of Other Financial Instrument [Line Items]
Loans held for sale	25	19
Estimate of fair value [Member] \| Consumer Loans [Member] \| Other consumer [Member]
Fair Value Of Other Financial Instrument [Line Items]
Loans held for sale	90	66
Estimate of fair value [Member] \| Deposits Without Fixed Maturities [Member]
Fair Value Of Other Financial Instrument [Line Items]
Deposits	109,625	105,962
Estimate of fair value [Member] \| Deposits With Fixed Maturities [Member]
Fair Value Of Other Financial Instrument [Line Items]
Deposits	$ 2,524	$ 2,813

Fair Value of Commercial Syndicated Loans Held For Sale

No definition available.

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- Definition

Interest bearing deposits domestic fair value option disclosure.

+ References

No definition available.

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- Definition

This element represents the portion of long term debt that the entity has elected to value at fair value under the fair value option.

+ References

No definition available.

+ Details

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Namespace Prefix:	hsbcusa_
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- Definition

Non-derivative trading assets fair value disclosure.

+ References

No definition available.

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- Definition

Non derivative trading liability.

+ References

No definition available.

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- Definition

Securities, Fair Value Disclosure

+ References

No definition available.

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- Definition

Short-term financial assets fair value disclosure.

+ References

No definition available.

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- Definition

Fair value portion of deposit liabilities held by the entity, including, but not limited to, foreign and domestic, interest and noninterest bearing, demand deposits, saving deposits, negotiable orders of withdrawal (NOW) and time deposits.

+ References

No definition available.

+ Details

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Period Type:	instant

- Definition

Fair value, after the effects of master netting arrangements, of a financial asset or other contract with one or more underlyings, notional amount or payment provision or both, and the contract can be net settled by means outside the contract or delivery of an asset. Includes assets not subject to a master netting arrangement and not elected to be offset.

+ 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 815

-SubTopic 10

-Section 45

-Paragraph 5

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-Name Accounting Standards Codification

-Topic 825

-SubTopic 10

-Section 50

-Paragraph 15

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-Publisher FASB

-Name Accounting Standards Codification

-Topic 210

-SubTopic 20

-Section 50

-Paragraph 3

-Subparagraph (c)

-URI http://asc.fasb.org/extlink&oid=34720828&loc=SL20225862-175312

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-Name Accounting Standards Codification

-Topic 815

-SubTopic 10

-Section 45

-Paragraph 6

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-Publisher FASB

-Name Accounting Standards Codification

-Topic 210

-SubTopic 20

-Section 55

-Paragraph 10

-URI http://asc.fasb.org/extlink&oid=36459792&loc=SL20226008-175313

+ Details

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

- Definition

Fair value, after the effects of master netting arrangements, of a financial liability or contract with one or more underlyings, notional amount or payment provision or both, and the contract can be net settled by means outside the contract or delivery of an asset. Includes liabilities not subject to a master netting arrangement and not elected to be offset.

+ References

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Namespace Prefix:	us-gaap_
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Balance Type:	credit
Period Type:	instant

- Details

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Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Definition

Fair value portion of federal funds sold and securities borrowed or purchased under agreements to resell.

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 942

-SubTopic 210

-Section S99

-Paragraph 1

-Subparagraph (SX 210.9-03.13(3)(a))

-URI http://asc.fasb.org/extlink&oid=6876686&loc=d3e534808-122878

+ Details

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

- Definition

Amount after allowance and deduction of deferred interest and fees, unamortized costs and premiums and discounts from face amounts, of commercial loans and leases receivable including, but not limited to, commercial and industrial loans, agricultural loans, mortgage loans, promissory notes, interbank and other loans to financial institutions, draws against credit facilities, trade financing, lease financings. Excludes loans and leases covered under loss sharing agreements.

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 310

-SubTopic 10

-Section 50

-Paragraph 4

-URI http://asc.fasb.org/extlink&oid=35738203&loc=d3e5074-111524

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-Publisher FASB

-Name Accounting Standards Codification

-Topic 310

-SubTopic 10

-Section 45

-Paragraph 2

-URI http://asc.fasb.org/extlink&oid=28367877&loc=d3e4428-111522

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-Publisher FASB

-Name Accounting Standards Codification

-Topic 310

-SubTopic 10

-Section 50

-Paragraph 3

-URI http://asc.fasb.org/extlink&oid=35738203&loc=d3e5066-111524

+ Details

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

- Definition

Amount after allowance and deduction of deferred interest and fees, unamortized costs and premiums and discounts from face amounts, of consumer loans, including, but not limited to, mortgage, home equity, vehicles, credit card, installment, and lease financing. Excludes loans and leases covered under loss sharing agreements.

+ References

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Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
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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Namespace Prefix:	us-gaap_
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Period Type:	instant

- Definition

The fair value amount of long-term debt whether such amount is presented as a separate caption or as a parenthetical disclosure. Additionally, this element may be used in connection with the fair value disclosures required in the footnote disclosures to the financial statements. The element may be used in both the balance sheet and disclosure in the same submission.

+ References

No definition available.

+ Details

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

- Definition

This element represents the portion of the balance sheet assertion valued at fair value by the entity whether such amount is presented as a separate caption or as a parenthetical disclosure. Additionally, this element may be used in connection with the fair value disclosures required in the footnote disclosures to the financial statements. The element may be used in both the balance sheet and disclosure in the same submission. This item represents the amount of short-term debt existing as of the balance sheet date.

+ References

No definition available.

+ Details

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Period Type:	instant

- Details

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- Details

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