Related Party Transactions - Summary of Related Party Transactions (Income - Expense) (Details) - USD ($) $ in Millions		3 Months Ended
		Mar. 31, 2016	Mar. 31, 2015
Related Party Transaction [Line Items]
Interest income		$ 980	$ 833
Interest expense		(326)	(227)
Net interest income	[1]	654	606
Trading revenue (expense)		16	33
Servicing and other fees with HSBC affiliates:
Total affiliate income		54	56
Gain (loss) on instruments designated at fair value and related derivatives		216	85
Support services from HSBC affiliates:
Total support services from HSBC affiliates		(320)	(352)
Affiliated Entity [Member]
Related Party Transaction [Line Items]
Interest income		30	30
Interest expense		(29)	(14)
Net interest income		1	16
Trading revenue (expense)		(157)	148
Servicing and other fees with HSBC affiliates:
Gain (loss) on instruments designated at fair value and related derivatives		(44)	258
Support services from HSBC affiliates:
Total support services from HSBC affiliates		(320)	(352)
Stock based compensation expense with HSBC	[2]	(6)	(13)
HSBC Markets (USA) Inc. (HMUS) and subsidiaries [Member]
Support services from HSBC affiliates:
Total support services from HSBC affiliates		(53)	(64)
Other Affiliates [Member]
Support services from HSBC affiliates:
Total support services from HSBC affiliates		(38)	(48)
HSBC Technology and Services (USA) (HTSU) [Member]
Support services from HSBC affiliates:
Total support services from HSBC affiliates		(229)	(240)
Fees and Commissions [Member] | HSBC Bank Plc [Member]
Servicing and other fees with HSBC affiliates:
Total affiliate income		22	19
Fees and Commissions [Member] | HSBC Finance Corporation [Member]
Servicing and other fees with HSBC affiliates:
Total affiliate income		13	16
Fees and Commissions [Member] | HSBC Markets (USA) Inc. (HMUS) and subsidiaries [Member]
Servicing and other fees with HSBC affiliates:
Total affiliate income		6	7
Fees and Commissions [Member] | Other Affiliates [Member]
Servicing and other fees with HSBC affiliates:
Total affiliate income		13	14
Other Fees [Member] | Affiliated Entity [Member]
Servicing and other fees with HSBC affiliates:
Total affiliate income		$ 54	$ 56

[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."