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, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016	Dec. 31, 2016
Assets:
Cash		$ 26		$ 26		$ 128
Interest bearing deposits with banks		0		0		1,500
Securities purchased under agreements to resell		4,040		4,040		2,392
Other assets		983		983		427
Total assets		8,024		8,024		13,882
Liabilities
Due to affiliates		0		0		3,300
Other liabilities		344		344		610
Total liabilities		2,340		$ 2,340		8,448
General term of securities purchased under an agreement to resell				120 days
Income/(Expense):
Servicing and other fees from HSBC affiliates		0	$ 1	$ 1	$ 7
Support services from HSBC affiliates		(15)	(40)	(59)	(120)
Loss on extinguishment of debt held by HSBC affiliates				(287)	0
HSBC affiliates [Member]
Assets:
Cash		26		26		128
Interest bearing deposits with banks		0		0
Securities purchased under agreements to resell	[1]	4,040		4,040		2,392
Other assets		124		124		114
Total assets		4,190		4,190		4,134
Liabilities
Due to affiliates	[2]	0		0		3,300
Other liabilities		14		14		41
Total liabilities		14		14		$ 3,341
Income/(Expense):
Interest income from HSBC affiliates		15	1	35	4
Interest expense paid to HSBC affiliates	[3]	(12)	(45)	(53)	(189)
Net interest income (expense)		3	(44)	(18)	(185)
Servicing and other fees from HSBC affiliates		0	1	1	7
Support services from HSBC affiliates		(15)	(40)	(59)	(120)
Loss on extinguishment of debt held by HSBC affiliates		(85)	0	(113)	0
Stock based compensation income (expense) with HSBC	[4]	(1)	(1)	(2)	(1)
Borrowings [Member] | HSBC affiliates [Member]
Income/(Expense):
Gain (loss) on FVO debt with affiliate		$ 7	$ (13)	$ 9	$ (1)

[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] 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 benefit plans sponsored by HSBC North America which are discussed in Note 8, "Pension and Other Postretirement Benefits."