Fair Value Measurements - Carrying Value and Estimated Fair Value of Financial Instruments (Detail) (USD $) In Millions, unless otherwise specified	Jun. 30, 2014	Dec. 31, 2013
Fair Value Of Other Financial Instrument [Line Items]
Federal funds sold and securities purchased under resale agreements	$ 2,311	$ 2,119
Commercial loans designated under fair value option and held for sale	159	58
Loans held for sale	500	230
Deposits designated under fair value option	7,714	7,740
Long-term debt designated under fair value option	8,300	7,600
Commercial Loan [Member]
Fair Value Of Other Financial Instrument [Line Items]
Loans held for sale	396	76
Consumer Loans [Member]
Fair Value Of Other Financial Instrument [Line Items]
Loans held for sale	104	154
Consumer Loans [Member] \| Residential Mortgage [Member]
Fair Value Of Other Financial Instrument [Line Items]
Loans held for sale	38	91
Consumer Loans [Member] \| Other consumer [Member]
Fair Value Of Other Financial Instrument [Line Items]
Loans held for sale	66	63
Level 1 [Member]
Fair Value Of Other Financial Instrument [Line Items]
Short-term financial assets	2,325	961
Federal funds sold and securities purchased under resale agreements	0	0
Non-derivative trading assets	2,717	1,344
Derivatives	10	26
Securities	27,924	39,553
Commercial loans, net of allowance for credit losses	0	0
Commercial loans designated under fair value option and held for sale	0	0
Consumer loans, net of allowance for credit losses	0	0
Short-term financial liabilities	0	0
Deposits without fixed maturities	0	0
Deposits with fixed maturities	0	0
Deposits designated under fair value option	0	0
Non-derivative trading liabilities	656	308
Derivatives	14	5
Long-term debt	0	0
Long-term debt designated under fair value option	0	0
Level 1 [Member] \| Commercial Loan [Member]
Fair Value Of Other Financial Instrument [Line Items]
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 2 [Member]
Fair Value Of Other Financial Instrument [Line Items]
Short-term financial assets	23,946	19,614
Federal funds sold and securities purchased under resale agreements	2,311	2,119
Non-derivative trading assets	15,006	18,924
Derivatives	5,828	7,467
Securities	18,226	16,852
Commercial loans, net of allowance for credit losses	0	0
Commercial loans designated under fair value option and held for sale	159	58
Consumer loans, net of allowance for credit losses	0	0
Short-term financial liabilities	12,924	19,154
Deposits without fixed maturities	105,977	102,584
Deposits with fixed maturities	1,834	2,289
Deposits designated under fair value option	5,457	5,406
Non-derivative trading liabilities	3,152	3,826
Derivatives	5,715	7,294
Long-term debt	17,022	15,729
Long-term debt designated under fair value option	7,525	6,686
Level 2 [Member] \| Commercial Loan [Member]
Fair Value Of Other Financial Instrument [Line Items]
Loans held for sale	237	18
Level 2 [Member] \| Consumer Loans [Member] \| Residential Mortgage [Member]
Fair Value Of Other Financial Instrument [Line Items]
Loans held for sale	14	36
Level 2 [Member] \| Consumer Loans [Member] \| Other consumer [Member]
Fair Value Of Other Financial Instrument [Line Items]
Loans held for sale	0	0
Level 3 [Member]
Fair Value Of Other Financial Instrument [Line Items]
Short-term financial assets	64	51
Federal funds sold and securities purchased under resale agreements	0	0
Non-derivative trading assets	3,079	2,635
Derivatives	44	76
Securities	0	0
Commercial loans, net of allowance for credit losses	54,210	49,897
Commercial loans designated under fair value option and held for sale	0	0
Consumer loans, net of allowance for credit losses	16,732	16,051
Short-term financial liabilities	63	51
Deposits without fixed maturities	0	0
Deposits with fixed maturities	0	0
Deposits designated under fair value option	2,257	2,334
Non-derivative trading liabilities	0	0
Derivatives	18	49
Long-term debt	0	0
Long-term debt designated under fair value option	738	900
Level 3 [Member] \| Commercial Loan [Member]
Fair Value Of Other Financial Instrument [Line Items]
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	24	56
Level 3 [Member] \| Consumer Loans [Member] \| Other consumer [Member]
Fair Value Of Other Financial Instrument [Line Items]
Loans held for sale	66	63
Carrying Value [Member]
Fair Value Of Other Financial Instrument [Line Items]
Short-term financial assets	26,335	20,626
Federal funds sold and securities purchased under resale agreements	2,311	2,119
Non-derivative trading assets	20,802	22,903
Derivatives	5,882	7,569
Securities	46,081	56,368
Commercial loans, net of allowance for credit losses	52,650	48,186
Commercial loans designated under fair value option and held for sale	159	58
Consumer loans, net of allowance for credit losses	18,924	18,903
Short-term financial liabilities	12,987	19,205
Deposits without fixed maturities	105,977	102,584
Deposits with fixed maturities	1,830	2,284
Deposits designated under fair value option	7,714	7,740
Non-derivative trading liabilities	3,808	4,134
Derivatives	5,747	7,348
Long-term debt	16,341	15,261
Long-term debt designated under fair value option	8,263	7,586
Carrying Value [Member] \| Commercial Loan [Member]
Fair Value Of Other Financial Instrument [Line Items]
Loans held for sale	237	18
Carrying Value [Member] \| Consumer Loans [Member] \| Residential Mortgage [Member]
Fair Value Of Other Financial Instrument [Line Items]
Loans held for sale	38	91
Carrying Value [Member] \| Consumer Loans [Member] \| Other consumer [Member]
Fair Value Of Other Financial Instrument [Line Items]
Loans held for sale	66	63
Estimate of fair value [Member]
Fair Value Of Other Financial Instrument [Line Items]
Short-term financial assets	26,335	20,626
Federal funds sold and securities purchased under resale agreements	2,311	2,119
Non-derivative trading assets	20,802	22,903
Derivatives	5,882	7,569
Securities	46,150	56,405
Commercial loans, net of allowance for credit losses	54,210	49,897
Commercial loans designated under fair value option and held for sale	159	58
Consumer loans, net of allowance for credit losses	16,732	16,051
Short-term financial liabilities	12,987	19,205
Deposits without fixed maturities	105,977	102,584
Deposits with fixed maturities	1,834	2,289
Deposits designated under fair value option	7,714	7,740
Non-derivative trading liabilities	3,808	4,134
Derivatives	5,747	7,348
Long-term debt	17,022	15,729
Long-term debt designated under fair value option	8,263	7,586
Estimate of fair value [Member] \| Commercial Loan [Member]
Fair Value Of Other Financial Instrument [Line Items]
Loans held for sale	237	18
Estimate of fair value [Member] \| Consumer Loans [Member] \| Residential Mortgage [Member]
Fair Value Of Other Financial Instrument [Line Items]
Loans held for sale	38	92
Estimate of fair value [Member] \| Consumer Loans [Member] \| Other consumer [Member]
Fair Value Of Other Financial Instrument [Line Items]
Loans held for sale	$ 66	$ 63

Deposits fixed maturities.

No definition available.

Name:	husi_DepositsFixedMaturities
Namespace Prefix:	husi_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Deposits without fixed maturities.

+ References

No definition available.

+ Details

Name:	husi_DepositsWithoutFixedMaturities
Namespace Prefix:	husi_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- 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

Name:	husi_LongTermDebtFairValueOptionDisclosure
Namespace Prefix:	husi_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Non-derivative trading assets fair value disclosure.

+ References

No definition available.

+ Details

Name:	husi_NonDerivativeTradingAssetsFairValue
Namespace Prefix:	husi_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Non derivative trading liability.

+ References

No definition available.

+ Details

Name:	husi_NonDerivativeTradingLiability
Namespace Prefix:	husi_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Securities, Fair Value Disclosure

+ References

No definition available.

+ Details

Name:	husi_SecuritiesFairValueDisclosure
Namespace Prefix:	husi_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Short-term financial assets fair value disclosure.

+ References

No definition available.

+ Details

Name:	husi_ShortTermFinancialAssetsFairValue
Namespace Prefix:	husi_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- 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

Name:	us-gaap_DepositsFairValueDisclosure
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
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=28364263&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

-URI http://asc.fasb.org/extlink&oid=6945355&loc=d3e41228-113958

Reference 3: 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=28364263&loc=d3e13495-108611

Reference 4: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 210

-SubTopic 20

-Section 50

-Paragraph 3

-Subparagraph (c)

-URI http://asc.fasb.org/extlink&oid=20225523&loc=SL20225862-175312

Reference 5: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 815

-SubTopic 10

-Section 45

-Paragraph 6

-URI http://asc.fasb.org/extlink&oid=6945355&loc=d3e41271-113958

Reference 6: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 210

-SubTopic 20

-Section 55

-Paragraph 10

-URI http://asc.fasb.org/extlink&oid=28370219&loc=SL20226008-175313

+ Details

Name:	us-gaap_DerivativeAssets
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 assets not subject to a master netting arrangement and not elected to be offset.

+ References

+ Details

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

- Details

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

- Definition

Includes: (1) the amount outstanding of funds lent to other depository institutions, securities brokers, or securities dealers in the form of Federal Funds sold; for example, immediately available funds lent under agreements or contracts that mature in one business day or roll over under a continuing contract, regardless of the nature of the transaction or the collateral involved, excluding overnight lending for commercial and industrial purposes. Also include Federal Funds sold under agreements to resell on a gross basis, excluding (1) sales of term Federal Funds, (2) due bills representing purchases of securities or other assets by the reporting bank that have not yet been delivered and similar instruments, (3) resale agreements that mature in more than one business day involving assets other than securities, and (4) yield maintenance dollar repurchase agreements (Federal Funds Sold) and (2) the dollar amount outstanding of funds lent in the form of security resale agreements regardless of maturity, if the agreement requires the bank to resell the identical security purchased or a security that meets the definition of substantially the same in the case of a dollar roll. Also include purchases of participations in pools of securities, regardless of maturity (Securities Purchased Under Agreements to Re-sell).

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 235

-SubTopic 10

-Section S99

-Paragraph 1

-Subparagraph (SX 210.4-08.(m)(2)(i))

-URI http://asc.fasb.org/extlink&oid=26873400&loc=d3e23780-122690

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

-Publisher SEC

-Name Regulation S-X (SX)

-Number 210

-Section 08

-Paragraph m

-Subparagraph 1(i)

-Article 4

+ Details

Name:	us-gaap_FederalFundsSoldAndSecuritiesPurchasedUnderAgreementsToResell
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=28368275&loc=d3e5074-111524

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

-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

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 310

-SubTopic 10

-Section 50

-Paragraph 3

-URI http://asc.fasb.org/extlink&oid=28368275&loc=d3e5066-111524

+ Details

Name:	us-gaap_LoansAndLeasesReceivableNetReportedAmountCommercial
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

+ Details

Name:	us-gaap_LoansAndLeasesReceivableNetReportedAmountConsumer
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

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

- Definition

Amount of loans held for sale, including but not limited to, commercial and consumer loans. Excludes loans and leases covered under loss sharing agreements and loans classified as debt securities.

+ References

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

-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

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

-Publisher SEC

-Name Regulation S-X (SX)

-Number 210

-Section 03

-Paragraph 7

-Subparagraph a

-Article 9

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 942

-SubTopic 210

-Section S99

-Paragraph 1

-Subparagraph (SX 210.9-03.7(a))

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

Reference 4: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 310

-SubTopic 10

-Section 35

-Paragraph 49

-URI http://asc.fasb.org/extlink&oid=25442802&loc=d3e3084-111518

Reference 5: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 948

-SubTopic 310

-Section 30

-Paragraph 1

-URI http://asc.fasb.org/extlink&oid=6490209&loc=d3e48214-111002

+ Details

Name:	us-gaap_LoansReceivableHeldForSaleNet
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
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

Name:	us-gaap_LongTermDebtFairValue
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

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