Related Party Transactions - Summary of Related Party Transactions (Income - Expense) (Details) - USD ($) $ in Millions		3 Months Ended		9 Months Ended
		Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2015	Sep. 30, 2014
Related Party Transaction [Line Items]
Interest income		$ 893	$ 759	$ 2,595	$ 2,266
Interest expense		(276)	(216)	(746)	(531)
Net interest income	[1]	617	543	1,849	1,735
Trading revenue (expense)		(34)	(9)	23	139
Servicing and other fees with HSBC affiliates:
Total affiliate income		53	53	162	151
Gain on instruments designated at fair value and related derivatives		165	36	306	20
Support services from HSBC affiliates:
Total support services from HSBC affiliates		(361)	(388)	(1,098)	(1,127)
Affiliated Entity [Member]
Related Party Transaction [Line Items]
Interest income		28	14	86	43
Interest expense		(19)	(19)	(41)	(56)
Net interest income		9	(5)	45	(13)
Trading revenue (expense)		72	(546)	441	159
Servicing and other fees with HSBC affiliates:
Gain on instruments designated at fair value and related derivatives		(535)	(80)	(405)	284
Support services from HSBC affiliates:
Total support services from HSBC affiliates		(361)	(388)	(1,098)	(1,127)
Stock based compensation expense with HSBC	[2]	(12)	(18)	(40)	(36)
HSBC Markets (USA) Inc. (HMUS) and subsidiaries [Member]
Support services from HSBC affiliates:
Total support services from HSBC affiliates		(66)	(56)	(199)	(167)
Other Affiliates [Member]
Support services from HSBC affiliates:
Total support services from HSBC affiliates		(45)	(58)	(145)	(162)
HSBC Technology and Services (USA) (HTSU) [Member]
Support services from HSBC affiliates:
Total support services from HSBC affiliates		(250)	(274)	(754)	(798)
Fees and Commissions [Member] | HSBC Bank Plc [Member]
Servicing and other fees with HSBC affiliates:
Total affiliate income		23	12	60	38
Fees and Commissions [Member] | HSBC Finance Corporation [Member]
Servicing and other fees with HSBC affiliates:
Total affiliate income		11	22	40	63
Fees and Commissions [Member] | HSBC Markets (USA) Inc. (HMUS) and subsidiaries [Member]
Servicing and other fees with HSBC affiliates:
Total affiliate income		6	8	19	15
Fees and Commissions [Member] | Other Affiliates [Member]
Servicing and other fees with HSBC affiliates:
Total affiliate income		13	11	43	35
Other Fees [Member] | Affiliated Entity [Member]
Servicing and other fees with HSBC affiliates:
Total affiliate income		$ 53	$ 53	$ 162	$ 151

[1] Net interest income of each segment represents the difference between actual interest earned on assets and interest paid on liabilities of the segment adjusted for a funding charge or credit. Segments are charged a cost to fund assets (e.g. customer loans) and receive a funding credit for funds provided (e.g. customer deposits) based on equivalent market rates. The objective of these charges/credits is to transfer interest rate risk from the segments to one centralized unit in Balance Sheet Management and more appropriately reflect the profitability of segments.

[2] Employees may participate in one or more stock compensation plans sponsored by HSBC. These expenses are included in salaries and employee benefits in our consolidated statement of income. Employees also may participate in a defined benefit pension plan and other postretirement plans sponsored by HSBC North America which are discussed in Note 12, "Pension and Other Postretirement Benefits."