Related Party Transactions - Related Party Balances and Income and (Expense) Generated by Related Party Transactions (Detail) - USD ($) $ in Millions		3 Months Ended		9 Months Ended
		Sep. 30, 2016	Sep. 30, 2015	Sep. 30, 2016	Sep. 30, 2015	Dec. 31, 2015
Assets:
Cash		$ 120		$ 120		$ 124
Securities purchased under agreements to resell		824		824		2,724
Other assets		1,123		1,123		1,021
Total assets		15,343		15,343		24,145
Liabilities
Due to affiliates		4,824		4,824		5,925
Other liabilities		430		430		1,773
Total liabilities		9,967		9,967		17,510
Income/(Expense):
Servicing and other fees from HSBC affiliates		1	$ 5	7	$ 17
Support services from HSBC affiliates		(40)	(54)	(120)	(166)
HSBC affiliates [Member]
Assets:
Cash		120		120		124
Securities purchased under agreements to resell	[1]	824		824		2,724
Other assets		78		78		128
Total assets		1,022		1,022		2,976
Liabilities
Due to affiliates	[2]	4,824		4,824		5,925
Other liabilities		18		18		62
Total liabilities		4,842		4,842		$ 5,987
Income/(Expense):
Interest income from HSBC affiliates		1	1	4	5
Interest expense paid to HSBC affiliates	[3]	(45)	(75)	(189)	(228)
Net interest income (expense)		(44)	(74)	(185)	(223)
Servicing and other fees from HSBC affiliates		1	5	7	17
Support services from HSBC affiliates		(40)	(54)	(120)	(166)
Stock based compensation expense with HSBC	[4]	(1)	(1)	(1)	(2)
Borrowings [Member] | HSBC affiliates [Member]
Income/(Expense):
Gain (loss) on FVO debt with affiliate		$ (13)	$ (6)	$ (1)	$ 7

[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 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] Certain employees 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 also participate in a defined benefit pension plan and other postretirement benefit plans sponsored by HSBC North America which are discussed in Note 8, “Pension and Other Postretirement Benefits.”