Related Party Transactions - Summary of Related Party Transactions (Income - Expense) (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2023	Jun. 30, 2022	Jun. 30, 2023	Jun. 30, 2022
Income (Expense):
Interest income	$ 1,723	$ 783	$ 3,327	$ 1,395
Interest expense	(1,289)	(251)	(2,410)	(386)
Net interest income	434	532	917	1,009
Trading revenue (expense)	228	61	453	133
Servicing and other fees from HSBC affiliates:
Gain (loss) on instruments designated at fair value and related derivatives	2	19	(20)	25
Support services from HSBC affiliates:
Total support services from HSBC affiliates	(425)	(419)	(809)	(837)
Related Party
Income (Expense):
Interest income	57	16	114	22
Interest expense	(124)	(60)	(243)	(112)
Net interest income	(67)	(44)	(129)	(90)
Trading revenue (expense)	(637)	1,330	(1,415)	2,605
Servicing and other fees from HSBC affiliates:
Gain (loss) on instruments designated at fair value and related derivatives	268	(894)	700	(1,290)
Support services from HSBC affiliates:
Total support services from HSBC affiliates	(425)	(419)	(809)	(837)
Rental income from HSBC affiliates, net	7	9	16	19
Stock based compensation expense	(5)	(3)	(10)	(7)
HSBC Markets (USA) Inc. ("HMUS")
Support services from HSBC affiliates:
Total support services from HSBC affiliates	(55)	(46)	(108)	(83)
Other HSBC affiliates
Support services from HSBC affiliates:
Total support services from HSBC affiliates	(125)	(129)	(236)	(250)
HTSU
Support services from HSBC affiliates:
Total support services from HSBC affiliates	(245)	(244)	(465)	(504)
Servicing and other fees from HSBC affiliates
Servicing and other fees from HSBC affiliates:
Other revenues	77	87	151	188
Servicing and other fees from HSBC affiliates | Related Party
Servicing and other fees from HSBC affiliates:
Other revenues	77	87	151	188
Servicing and other fees from HSBC affiliates | HSBC Bank plc
Servicing and other fees from HSBC affiliates:
Other revenues	37	48	78	108
Servicing and other fees from HSBC affiliates | HSBC Markets (USA) Inc. ("HMUS")
Servicing and other fees from HSBC affiliates:
Other revenues	19	17	37	42
Servicing and other fees from HSBC affiliates | Other HSBC affiliates
Servicing and other fees from HSBC affiliates:
Other revenues	$ 21	$ 22	$ 36	$ 38