Related Party Transactions - Summary of Related Party Transactions (Income - Expense) (Details) - USD ($) $ in Millions		3 Months Ended
		Mar. 31, 2017	Mar. 31, 2016
Related Party Transaction [Line Items]
Interest income		$ 1,015	$ 980
Interest expense		(418)	(326)
Net interest income	[1]	597	654
Trading revenue (expense)		70	16
Servicing and other fees with HSBC affiliates:
Total affiliate income		82	54
Gain (loss) on instruments designated at fair value and related derivatives		34	216
Support services from HSBC affiliates:
Total support services from HSBC affiliates		(339)	(320)
Affiliated Entity [Member]
Related Party Transaction [Line Items]
Interest income		24	30
Interest expense		(66)	(29)
Net interest income		(42)	1
Trading revenue (expense)		85	(157)
Servicing and other fees with HSBC affiliates:
Total affiliate income		82	54
Gain (loss) on instruments designated at fair value and related derivatives		360	(44)
Support services from HSBC affiliates:
Total support services from HSBC affiliates		(339)	(320)
Stock based compensation expense with HSBC	[2]	(7)	(6)
HSBC Bank Plc [Member]
Servicing and other fees with HSBC affiliates:
Total affiliate income		24	22
HSBC Finance Corporation [Member]
Servicing and other fees with HSBC affiliates:
Total affiliate income		34	13
HSBC Markets (USA) Inc. (HMUS) and subsidiaries [Member]
Servicing and other fees with HSBC affiliates:
Total affiliate income		5	6
Support services from HSBC affiliates:
Total support services from HSBC affiliates		(12)	(53)
Other Affiliates [Member]
Servicing and other fees with HSBC affiliates:
Total affiliate income		19	13
Support services from HSBC affiliates:
Total support services from HSBC affiliates		(42)	(38)
HSBC Technology and Services (USA) (HTSU) [Member]
Support services from HSBC affiliates:
Total support services from HSBC affiliates		$ (285)	$ (229)

[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 the 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. Certain employees are also eligible to participate in a defined benefit pension plan and other postretirement plans sponsored by HSBC North America which are discussed in Note 11, "Pension and Other Postretirement Benefits.