Related Party Transactions - Related Party Balances and Income and (Expense) Generated by Related Party Transactions (Parenthetical) (Detail) (USD $)	12 Months Ended
Dec. 31, 2012	Dec. 31, 2011
Related Party Transaction [Line Items]
Long-term debt	$ 28,426,000,000	$ 39,790,000,000
HSBC North America [Member]
Related Party Transaction [Line Items]
Due to Affiliate	514,000,000	447,000,000
Long-term debt		600,000,000
Debt Instrument Face Amount Second Borrowing Amount	200,000,000
Debt Instrument Face Amount Third Borrowing Amount	200,000,000
HSBC USA Inc [Member]
Related Party Transaction [Line Items]
Extended Secured Uncommitted Secured Credit Facility To Subsidiaries		1,500,000,000
Credit card receivables	0	0
Line Of Credit Facility Expiration Year	2017-09
Commercial paper back-stop credit facility [Member] \| HSBC Investments [Member]
Related Party Transaction [Line Items]
Credit card receivables	0	0
Maturity Year Of Line Of Credit	2014-04
Commercial paper back-stop credit facility [Member] \| HSBC Trinkaus & Burkhardt AG [Member]
Related Party Transaction [Line Items]
Credit card receivables	0	0
Maturity Year Of Line Of Credit	2012-12
Commercial Back Facility Maturity 2012 [Member] \| HSBC USA Inc [Member]
Related Party Transaction [Line Items]
Line Of Credit Facility Expiration Year	2012-09
Delayed Draw Term Loan [Member] \| HSBC North America [Member]
Related Party Transaction [Line Items]
Long-term debt	$ 600,000,000

Amount of payable due to an entity that is affiliated with the reporting entity by means of direct or indirect ownership.

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 946

-SubTopic 210

-Section S99

-Paragraph 1

-Subparagraph (SX 210.6-04.12(3))

-URI http://asc.fasb.org/extlink&oid=6488278&loc=d3e603758-122996

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

-Publisher FASB

-Name Accounting Standards Codification

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-SubTopic 10

-Section 50

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

-Publisher SEC

-Name Regulation S-X (SX)

-Number 210

-Section 08

-Paragraph k

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

-Publisher SEC

-Name Regulation S-X (SX)

-Number 210

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-Paragraph 15

-Subparagraph 3

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 235

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-Section S99

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-URI http://asc.fasb.org/extlink&oid=6881521&loc=d3e23780-122690

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 942

-SubTopic 210

-Section S99

-Paragraph 1

-Subparagraph (SX 210.9-03.15(3))

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

Reference 7: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 944

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-URI http://asc.fasb.org/extlink&oid=6879938&loc=d3e572229-122910

Reference 8: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

-Number 57

-Paragraph 2

-Subparagraph d

-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.

Reference 9: http://www.xbrl.org/2003/role/presentationRef

-Publisher SEC

-Name Regulation S-X (SX)

-Number 210

-Section 03

-Paragraph 17

-Article 7

+ Details

- Definition

Carrying amount of long-term debt, net of unamortized discount or premium, including current and noncurrent amounts. Includes, but not limited to, notes payable, bonds payable, debentures, mortgage loans and commercial paper. Excludes capital lease obligations.

+ References+ Details