Related Party Transactions - Additional Information (Detail)			1 Months Ended		3 Months Ended		12 Months Ended
		Oct. 17, 2013 USD ($)	Nov. 30, 2013 USD ($)	Oct. 31, 2013 USD ($)	Sep. 30, 2015 USD ($)	Dec. 31, 2010 USD ($) shares	Dec. 31, 2015 USD ($) borrowing	Dec. 31, 2014 USD ($)	Dec. 31, 2013 USD ($)	Oct. 31, 2015 USD ($)
Related Party Transaction [Line Items]
General term of securities purchased under an agreement to resell							120 days
Litigation judgment claims		$ 2,500,000,000
Due to affiliates							$ 5,925,000,000	$ 6,945,000,000
Long-term debt							9,510,000,000	16,427,000,000
Notional values of derivative contracts							8,933,000,000	13,980,000,000
Fair value of our agreements with affiliate counterparties required the affiliate to provide collateral							491,000,000	213,000,000
Interest bearing deposits with banks							0	2,000,000,000
HSBC USA, Inc. [Member]
Related Party Transaction [Line Items]
Due to affiliates							$ 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							$ 1,600,000,000	600,000,000
Annual fee to guarantor							4,000,000	6,000,000
HSBC North America [Member] | Revolving Credit Facility [Member]
Related Party Transaction [Line Items]
Borrowing capacity of credit facility					$ 1,000,000,000			455,000,000		$ 1,000,000,000
Debt instrument, term					364 days
HSBC affiliates [Member]
Related Party Transaction [Line Items]
Due to affiliates	[1]						5,925,000,000	6,945,000,000
Interest bearing deposits with banks							0	2,000,000,000
Interest income on deposits								0	$ 0
Cash received from sale of data center							54,000,000
HSBC Bank USA [Member]
Related Party Transaction [Line Items]
Notional values of derivative contracts							8,900,000,000	14,000,000,000
Receivables services to affiliates							696,000,000	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							86,000,000	86,000,000	$ 86,000,000
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
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
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
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
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
Amount of credit facility outstanding							0	$ 0
Subordinated Debt [Member] | Public Subordinated Debt Issue Maturing 2021 [Member]
Related Party Transaction [Line Items]
Long-term debt							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
Number of draws allowed | borrowing							3
Amount per draw							$ 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]
Litigation judgment claims			$ 2,500,000,000	$ 2,500,000,000

[1] Due to affiliates includes amounts owed to HSBC and its subsidiaries as a result of direct debt issuances and excludes preferred stock.