Related Party Transactions - Additional Information (Detail) (USD $)	9 Months Ended				9 Months Ended	3 Months Ended	9 Months Ended			9 Months Ended			9 Months Ended		3 Months Ended			9 Months Ended																		9 Months Ended
	Sep. 30, 2014	Dec. 31, 2013	Sep. 30, 2014 HSBC USA, Inc. [Member]	Dec. 31, 2013 HSBC USA, Inc. [Member]	Sep. 30, 2014 HSBC USA, Inc. [Member] Revolving Credit Facility [Member]	Sep. 30, 2014 HSBC North America [Member]	Sep. 30, 2014 HSBC North America [Member]	Dec. 31, 2013 HSBC North America [Member]	Sep. 30, 2014 HSBC North America [Member] Revolving Credit Facility [Member]	Sep. 30, 2014 Hsbc Investments [Member] Revolving Credit Facility [Member]	Sep. 30, 2014 HSBC USA Inc [Member]	Dec. 31, 2013 HSBC USA Inc [Member]	Sep. 30, 2014 HSBC Asia [Member] loan_agreement	Dec. 31, 2013 HSBC Asia [Member]	Sep. 30, 2014 Series C Preferred Stock [Member]	Sep. 30, 2013 Series C Preferred Stock [Member]	Dec. 31, 2010 Series C Preferred Stock [Member]	Sep. 30, 2014 Series C Preferred Stock [Member]	Sep. 30, 2013 Series C Preferred Stock [Member]	Sep. 30, 2014 Amended Credit Agreement [Member] HSBC USA, Inc. [Member] Revolving Credit Facility [Member]	Sep. 30, 2014 Amended Credit Agreement Maturing September 2017 [Member] HSBC USA, Inc. [Member] Revolving Credit Facility [Member]	Sep. 30, 2014 Amended Credit Agreement Maturing January 2018 [Member] HSBC USA, Inc. [Member] Revolving Credit Facility [Member]	Sep. 30, 2014 Amended Credit Agreement Maturing September 2018 [Member] HSBC USA, Inc. [Member] Revolving Credit Facility [Member]	Sep. 30, 2014 Loan Maturing in 2014 [Member] HSBC Asia [Member]	Sep. 30, 2014 Loan Maturing in 2015 [Member] HSBC Asia [Member]	Sep. 30, 2014 Maturing May 2017 [Member] HSBC USA, Inc. [Member] Revolving Credit Facility [Member]	Dec. 31, 2013 Maturing May 2017 [Member] HSBC USA, Inc. [Member] Revolving Credit Facility [Member]	Sep. 30, 2014 Maturing April 2014 [Member] Hsbc Investments [Member] Revolving Credit Facility [Member]	Dec. 31, 2013 Maturing April 2014 [Member] Hsbc Investments [Member] Revolving Credit Facility [Member]	Sep. 30, 2014 Maturing January 2015 [Member] HSBC North America [Member] Revolving Credit Facility [Member]	Dec. 31, 2013 Maturing January 2015 [Member] HSBC North America [Member] Revolving Credit Facility [Member]	Sep. 30, 2014 Parent Company [Member]	Dec. 31, 2013 Parent Company [Member]	Sep. 30, 2014 Subordinated Debt [Member] Public Subordinated Debt Issue Maturing 2021 [Member]	Sep. 30, 2014 Delayed Draw Term Loan [Member] HSBC North America [Member] borrowing	Sep. 30, 2014 Delayed Draw Term Loan [Member] Minimum [Member] HSBC North America [Member]	Sep. 30, 2014 Delayed Draw Term Loan [Member] Maximum [Member] HSBC North America [Member]
Related Party Transaction [Line Items]
General term of securities purchased under an agreement to resell	120 days
Borrowing capacity of credit facility									$ 455,000,000											$ 5,000,000,000						$ 1,000,000,000		$ 100,000,000
Debt instrument, term					364 days					364 days
Annual fee to guarantor						1,000,000	4,000,000
Expiration period					5 years
Long-term debt	17,136,000,000	20,839,000,000																																3,000,000,000
Due to affiliates	6,940,000,000	8,742,000,000	3,012,000,000	3,012,000,000		600,000,000	600,000,000	600,000,000					0	10,000,000							512,000,000	1,500,000,000	1,000,000,000	5,000,000	5,000,000
Loan agreements with affiliates																																			600,000,000
Number of draws allowed																																			3
Amount per draw																																			200,000,000
Maturity year of long term debt																																				2034	2035
Number of loan agreements													2
Amount of credit facility outstanding																										0	0	0	0	0	0
Notional values of derivative contracts	13,980,000,000	16,467,000,000																														14,000,000,000	16,500,000,000
Fair value of our agreements with affiliate counterparties required the affiliate to provide collateral	190,000,000	811,000,000
Number of shares of stock issued (shares)																	1,000
Value of issued stock																	1,000,000,000
Dividend paid on preferred stock															21,000,000	21,000,000		64,000,000	64,000,000
Receivables services to affiliates											$ 867,000,000	$ 1,000,000,000