Related Party Transactions - Summary of Related Party Transactions (Income - Expense) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Income (Expense):
Interest income	$ 7,049	$ 3,905	$ 2,675
Interest expense	(5,344)	(1,836)	(592)
Net interest income	1,705	2,069	2,083
Trading revenue (expense)	942	517	24
Servicing and other fees from HSBC affiliates:
Gain (loss) on instruments designated at fair value and related derivatives	(42)	(50)	35
Support services from HSBC affiliates:
Total support services from HSBC affiliates	(1,671)	(1,762)	(1,620)
Related Party
Income (Expense):
Interest income	223	116	26
Interest expense	(501)	(298)	(237)
Net interest income	(278)	(182)	(211)
Trading revenue (expense)	(3,287)	1,753	(3,182)
Servicing and other fees from HSBC affiliates:
Gain (loss) on instruments designated at fair value and related derivatives	936	(1,256)	1,128
Support services from HSBC affiliates:
Total support services from HSBC affiliates	(1,671)	(1,762)	(1,620)
Rental income from HSBC affiliates, net	33	39	42
Stock based compensation expense	(19)	(15)	(15)
HSBC Markets (USA) Inc. ("HMUS")
Support services from HSBC affiliates:
Total support services from HSBC affiliates	(230)	(191)	(118)
Other HSBC affiliates
Support services from HSBC affiliates:
Total support services from HSBC affiliates	(489)	(553)	(441)
HTSU
Support services from HSBC affiliates:
Total support services from HSBC affiliates	(952)	(1,018)	(1,061)
Servicing and other fees from HSBC affiliates
Servicing and other fees from HSBC affiliates:
Other revenues	327	343	321
Servicing and other fees from HSBC affiliates | Related Party
Servicing and other fees from HSBC affiliates:
Other revenues	327	343	321
Servicing and other fees from HSBC affiliates | HSBC Bank plc
Servicing and other fees from HSBC affiliates:
Other revenues	180	190	176
Servicing and other fees from HSBC affiliates | HSBC Markets (USA) Inc. ("HMUS")
Servicing and other fees from HSBC affiliates:
Other revenues	81	76	91
Servicing and other fees from HSBC affiliates | Other HSBC affiliates
Servicing and other fees from HSBC affiliates:
Other revenues	$ 66	$ 77	$ 54