Related Party Transactions - Summary of Related Party Transactions (Income - Expense) (Details) - USD ($) $ in Millions		3 Months Ended		9 Months Ended
		Sep. 30, 2016	Sep. 30, 2015	Sep. 30, 2016	Sep. 30, 2015
Related Party Transaction [Line Items]
Interest income		$ 966	$ 893	$ 2,926	$ 2,595
Interest expense		(362)	(276)	(1,030)	(746)
Net interest income	[1]	604	617	1,896	1,849
Trading revenue (expense)		120	(34)	185	23
Servicing and other fees with HSBC affiliates:
Total affiliate income		50	53	155	162
Gain (loss) on instruments designated at fair value and related derivatives		(88)	165	90	306
Support services from HSBC affiliates:
Total support services from HSBC affiliates		(354)	(361)	(1,029)	(1,098)
Affiliated Entity [Member]
Related Party Transaction [Line Items]
Interest income		30	28	90	86
Interest expense		(38)	(19)	(102)	(41)
Net interest income		(8)	9	(12)	45
Trading revenue (expense)		(661)	72	138	441
Servicing and other fees with HSBC affiliates:
Gain (loss) on instruments designated at fair value and related derivatives		193	(535)	228	(405)
Support services from HSBC affiliates:
Total support services from HSBC affiliates		(354)	(361)	(1,029)	(1,098)
Stock based compensation expense with HSBC	[2]	(7)	(12)	(24)	(40)
HSBC Markets (USA) Inc. (HMUS) and subsidiaries [Member]
Support services from HSBC affiliates:
Total support services from HSBC affiliates		(42)	(66)	(150)	(199)
Other Affiliates [Member]
Support services from HSBC affiliates:
Total support services from HSBC affiliates		(60)	(45)	(145)	(145)
HSBC Technology and Services (USA) (HTSU) [Member]
Support services from HSBC affiliates:
Total support services from HSBC affiliates		(252)	(250)	(734)	(754)
Fees and Commissions [Member] | HSBC Bank Plc [Member]
Servicing and other fees with HSBC affiliates:
Total affiliate income		22	23	70	60
Fees and Commissions [Member] | HSBC Finance Corporation [Member]
Servicing and other fees with HSBC affiliates:
Total affiliate income		8	11	29	40
Fees and Commissions [Member] | HSBC Markets (USA) Inc. (HMUS) and subsidiaries [Member]
Servicing and other fees with HSBC affiliates:
Total affiliate income		5	6	15	19
Fees and Commissions [Member] | Other Affiliates [Member]
Servicing and other fees with HSBC affiliates:
Total affiliate income		15	13	41	43
Other Fees [Member] | Affiliated Entity [Member]
Servicing and other fees with HSBC affiliates:
Total affiliate income		$ 50	$ 53	$ 155	$ 162

[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 13, "Pension and Other Postretirement Benefits."