Related Party Transactions - Summary of Related Party Transactions (Income - Expense) (Details) - USD ($) $ in Millions		3 Months Ended		6 Months Ended
		Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016
Related Party Transaction [Line Items]
Interest income		$ 1,042	$ 980	$ 2,057	$ 1,960
Interest expense		(460)	(342)	(878)	(668)
Net interest income	[1]	582	638	1,179	1,292
Trading revenue (expense)		71	49	141	65
Servicing and other fees with HSBC affiliates:
Total affiliate income		52	51	134	105
Gain on instruments designated at fair value and related derivatives		(1)	(38)	33	178
Support services from HSBC affiliates:
Total support services from HSBC affiliates		(355)	(355)	(694)	(675)
Affiliated Entity [Member]
Related Party Transaction [Line Items]
Interest income		11	30	35	60
Interest expense		(70)	(35)	(136)	(64)
Net interest income		(59)	(5)	(101)	(4)
Trading revenue (expense)		(891)	956	(806)	799
Servicing and other fees with HSBC affiliates:
Gain on instruments designated at fair value and related derivatives		164	79	524	35
Support services from HSBC affiliates:
Total support services from HSBC affiliates		(355)	(355)	(694)	(675)
Stock based compensation expense with HSBC	[2]	(11)	(11)	(18)	(17)
HSBC Markets (USA) Inc. (HMUS) and subsidiaries [Member]
Support services from HSBC affiliates:
Total support services from HSBC affiliates		(12)	(55)	(24)	(108)
Other Affiliates [Member]
Support services from HSBC affiliates:
Total support services from HSBC affiliates		(50)	(47)	(92)	(85)
HSBC Technology and Services (USA) (HTSU) [Member]
Support services from HSBC affiliates:
Total support services from HSBC affiliates		(293)	(253)	(578)	(482)
Fees and Commissions [Member] | HSBC Bank Plc [Member]
Servicing and other fees with HSBC affiliates:
Total affiliate income		21	26	45	48
Fees and Commissions [Member] | HSBC Finance Corporation [Member]
Servicing and other fees with HSBC affiliates:
Total affiliate income		3	8	37	21
Fees and Commissions [Member] | HSBC Markets (USA) Inc. (HMUS) and subsidiaries [Member]
Servicing and other fees with HSBC affiliates:
Total affiliate income		5	4	10	10
Fees and Commissions [Member] | Other Affiliates [Member]
Servicing and other fees with HSBC affiliates:
Total affiliate income		23	13	42	26
Other Fees [Member] | Affiliated Entity [Member]
Servicing and other fees with HSBC affiliates:
Total affiliate income		$ 52	$ 51	$ 134	$ 105

[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 (loss). 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.