Related Party Transactions - Related Party Balances and Income and (Expense) Generated by Related Party Transactions (Detail) (USD $) In Millions, unless otherwise specified	3 Months Ended
	Mar. 31, 2015		Mar. 31, 2014		Dec. 31, 2014
Assets:
Cash	$ 147				$ 157
Interest bearing deposits with banks	2,001				2,000
Securities purchased under agreements to resell	3,327				3,863
Other assets	1,277				1,109
Total assets	30,939				31,960
Liabilities
Due to affiliates	6,945				6,945
Other liabilities	1,111				1,091
Total liabilities	23,843				24,837
Income/(Expense):
Servicing and other fees from HSBC affiliates	6		8
Support services from HSBC affiliates	(54)		(60)
HSBC affiliates [Member]
Assets:
Cash	146				157
Interest bearing deposits with banks	2,001				2,000
Securities purchased under agreements to resell	3,327	[1]			3,863	[1]
Other assets	239				102
Total assets	5,713				6,122
Liabilities
Due to affiliates	6,945	[2]			6,945	[2]
Other liabilities	38				84
Total liabilities	6,983				7,029
Income/(Expense):
Interest income from HSBC affiliates	2		1
Interest expense paid to HSBC affiliates	(77)	[3]	(80)	[3]
Net interest income (loss)	(75)		(79)
Servicing and other fees from HSBC affiliates	6		8
Support services from HSBC affiliates	(54)		(60)
Stock based compensation expense with HSBC	(1)	[4]	(1)	[4]
HSBC affiliates [Member] | Borrowings [Member]
Income/(Expense):
Gain (loss) on FVO debt with affiliate	$ 0		$ (8)

[1] Securities under an agreement to resell are purchased from HSBC Securities (USA) Inc. and generally have terms of 120 days or less. The collateral underlying the securities purchased under agreements to resell, however, is with an unaffiliated third party. Interest income recognized on these securities is reflected as interest income from HSBC affiliate in the table below.

[2] Due to affiliates includes amounts owed to HSBC and its subsidiaries as a result of direct debt issuances as well as HSBC's ownership of our subordinated debt and excludes preferred stock.

[3] Includes interest expense paid to HSBC affiliates for debt held by HSBC affiliates as well as net interest paid to or received from HSBC affiliates on risk management hedges related to non-affiliated debt.

[4] Employees participate in one or more stock compensation plans sponsored by HSBC. These expenses are included in Salary and employee benefits in our consolidated statement of income. Employees also participate in a defined benefit pension plan and other postretirement benefit plans sponsored by HSBC North America which are discussed in Note 9, “Pension and Other Postretirement Benefits.”