Related Party Transactions - Additional Information (Detail)	3 Months Ended			6 Months Ended
	Jun. 30, 2015 USD ($) borrowing	Jun. 30, 2014 USD ($)	Dec. 31, 2010 USD ($) shares	Jun. 30, 2015 USD ($) borrowing	Jun. 30, 2014 USD ($)	Dec. 31, 2014 USD ($)	Nov. 30, 2013 USD ($)
Related Party Transaction [Line Items]
General term of securities purchased under an agreement to resell				120 days
Due to affiliates	$ 5,931,000,000			$ 5,931,000,000		$ 6,945,000,000
Long-term debt	12,988,000,000			12,988,000,000		16,427,000,000
Notional values of derivative contracts	12,157,000,000			12,157,000,000		13,980,000,000
Fair value of our agreements with affiliate counterparties required the affiliate to provide collateral	543,000,000			543,000,000		213,000,000
Interest bearing deposits with banks	2,002,000,000			2,002,000,000		2,000,000,000
HSBC USA, Inc. [Member]
Related Party Transaction [Line Items]
Due to affiliates	3,012,000,000			$ 3,012,000,000		3,012,000,000
HSBC USA, Inc. [Member] | Revolving Credit Facility [Member]
Related Party Transaction [Line Items]
Debt instrument, term				364 days
Maximum maturity period for borrowings				5 years
HSBC North America [Member]
Related Party Transaction [Line Items]
Due to affiliates	600,000,000			$ 600,000,000		600,000,000
Annual fee to guarantor	1,000,000	$ 2,000,000		3,000,000	$ 3,000,000
HSBC North America [Member] | Revolving Credit Facility [Member]
Related Party Transaction [Line Items]
Borrowing capacity of credit facility	455,000,000			$ 455,000,000		455,000,000
Debt instrument, term				364 days
HSBC Bank USA [Member]
Related Party Transaction [Line Items]
Notional values of derivative contracts	12,157,000,000			$ 12,157,000,000		13,980,000,000
Interest bearing deposits with banks	2,002,000,000			2,002,000,000		2,000,000,000
Interest income on deposits		0			0
Receivables services to affiliates	768,000,000			768,000,000		837,000,000
Series C Preferred Stock [Member]
Related Party Transaction [Line Items]
Number of shares of stock issued (shares) | shares			1,000
Value of issued stock			$ 1,000,000,000
Dividend paid on preferred stock	21,000,000	$ 21,000,000		43,000,000	$ 43,000,000
Amended Credit Agreement [Member] | HSBC USA, Inc. [Member] | Revolving Credit Facility [Member]
Related Party Transaction [Line Items]
Borrowing capacity of credit facility	5,000,000,000			5,000,000,000
Amended Credit Agreement Maturing September 2017 [Member] | HSBC USA, Inc. [Member] | Revolving Credit Facility [Member]
Related Party Transaction [Line Items]
Long-term debt due to affiliate	512,000,000			512,000,000
Amended Credit Agreement Maturing January 2018 [Member] | HSBC USA, Inc. [Member] | Revolving Credit Facility [Member]
Related Party Transaction [Line Items]
Due to affiliates	1,500,000,000			1,500,000,000
Amended Credit Agreement Maturing September 2018 [Member] | HSBC USA, Inc. [Member] | Revolving Credit Facility [Member]
Related Party Transaction [Line Items]
Due to affiliates	1,000,000,000			1,000,000,000
Maturing May 2017 [Member] | HSBC USA, Inc. [Member] | Revolving Credit Facility [Member]
Related Party Transaction [Line Items]
Borrowing capacity of credit facility	1,000,000,000			1,000,000,000		1,000,000,000
Amount of credit facility outstanding	0			0		$ 0
Subordinated Debt [Member] | Public Subordinated Debt Issue Maturing 2021 [Member]
Related Party Transaction [Line Items]
Long-term debt	3,000,000,000			3,000,000,000
Delayed Draw Term Loan [Member] | HSBC North America [Member]
Related Party Transaction [Line Items]
Loan agreements with affiliates	$ 600,000,000			$ 600,000,000
Number of draws allowed | borrowing	3			3
Amount per draw	$ 200,000,000			$ 200,000,000
Delayed Draw Term Loan [Member] | Minimum [Member] | HSBC North America [Member]
Related Party Transaction [Line Items]
Maturity year of long term debt				2034
Delayed Draw Term Loan [Member] | Maximum [Member] | HSBC North America [Member]
Related Party Transaction [Line Items]
Maturity year of long term debt				2035
Securities Litigation [Member]
Related Party Transaction [Line Items]
Amount of surety bond							$ 2,500,000,000