Related Party Transactions - Summary of Related Party Transactions (Income - Expense) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2024	Dec. 31, 2023	Dec. 31, 2022
Income (Expense):
Interest income	$ 7,667	$ 7,049	$ 3,905
Net interest income	1,767	1,705	2,069
Trading revenue (expense)	998	942	517
Servicing and other fees from HSBC affiliates:
Gain (loss) on instruments designated at fair value and related derivatives	(38)	(42)	(50)
Support services from HSBC affiliates:
Total support services from HSBC affiliates	(1,670)	(1,671)	(1,762)
Related Party
Income (Expense):
Interest income	247	223	116
Interest expense	(564)	(501)	(298)
Net interest income	(317)	(278)	(182)
Trading revenue (expense)	(1,070)	(3,287)	1,753
Servicing and other fees from HSBC affiliates:
Gain (loss) on instruments designated at fair value and related derivatives	222	936	(1,256)
Support services from HSBC affiliates:
Total support services from HSBC affiliates	(1,670)	(1,671)	(1,762)
Rental income from HSBC affiliates, net	50	33	39
Stock based compensation expense	(28)	(19)	(15)
HTSU
Support services from HSBC affiliates:
Total support services from HSBC affiliates	(942)	(952)	(1,018)
HSBC Markets (USA) Inc. ("HMUS")
Support services from HSBC affiliates:
Total support services from HSBC affiliates	(233)	(230)	(191)
Other HSBC affiliates
Support services from HSBC affiliates:
Total support services from HSBC affiliates	(495)	(489)	(553)
Servicing and other fees from HSBC affiliates
Servicing and other fees from HSBC affiliates:
Other revenues	385	327	343
Servicing and other fees from HSBC affiliates | Related Party
Servicing and other fees from HSBC affiliates:
Other revenues	385	327	343
Servicing and other fees from HSBC affiliates | HSBC Bank plc
Servicing and other fees from HSBC affiliates:
Other revenues	209	180	190
Servicing and other fees from HSBC affiliates | HSBC Markets (USA) Inc. ("HMUS")
Servicing and other fees from HSBC affiliates:
Other revenues	102	81	76
Servicing and other fees from HSBC affiliates | Other HSBC affiliates
Servicing and other fees from HSBC affiliates:
Other revenues	$ 74	$ 66	$ 77