Related Party Transactions - Summary of Related Party Transactions (Income - Expense) (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended
	Mar. 31, 2015		Mar. 31, 2014
Related Party Transaction [Line Items]
Interest income	$ 833		$ 745
Interest expense	(227)		(226)
Net interest income	606	[1]	519	[1]
Trading revenue	33		133
Servicing and other fees with HSBC affiliates:
Total affiliate income	56		47
Gain on instruments designated at fair value and related derivatives	85		28
Support services from HSBC affiliates:
Total support services from HSBC affiliates	(352)		(354)
Affiliated Entity [Member]
Related Party Transaction [Line Items]
Interest income	30		14
Interest expense	(14)		(18)
Net interest income	16		(4)
Trading revenue	148		852
Servicing and other fees with HSBC affiliates:
Gain on instruments designated at fair value and related derivatives	258		98
Support services from HSBC affiliates:
Total support services from HSBC affiliates	(352)		(354)
Stock based compensation expense with HSBC	(13)	[2]	(7)	[2]
HSBC Markets (USA) Inc. (HMUS) and subsidiaries [Member]
Support services from HSBC affiliates:
Total support services from HSBC affiliates	(64)		(57)
Other Affiliates [Member]
Support services from HSBC affiliates:
Total support services from HSBC affiliates	(48)		(44)
HSBC Technology and Services (USA) (HTSU) [Member]
Support services from HSBC affiliates:
Total support services from HSBC affiliates	(240)		(253)
Fees and Commissions [Member] | HSBC Bank Plc [Member]
Servicing and other fees with HSBC affiliates:
Total affiliate income	19		16
Fees and Commissions [Member] | HSBC Finance Corporation [Member]
Servicing and other fees with HSBC affiliates:
Total affiliate income	16		15
Fees and Commissions [Member] | HSBC Markets (USA) Inc. (HMUS) and subsidiaries [Member]
Servicing and other fees with HSBC affiliates:
Total affiliate income	7		4
Fees and Commissions [Member] | Other Affiliates [Member]
Servicing and other fees with HSBC affiliates:
Total affiliate income	14		12
Other Fees [Member] | Affiliated Entity [Member]
Servicing and other fees with HSBC affiliates:
Total affiliate income	$ 56		$ 47

[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."