Related Party Transactions - Summary of Related Party Transactions (Income - Expense) (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2024	Mar. 31, 2023
Income (Expense):
Interest income	$ 1,893	$ 1,604
Interest expense	(1,467)	(1,121)
Net interest income	426	483
Trading revenue (expense)	276	225
Servicing and other fees from HSBC affiliates:
Gain on instruments designated at fair value and related derivatives	(20)	(22)
Support services from HSBC affiliates:
Total support services from HSBC affiliates	(399)	(384)
Related Party
Income (Expense):
Interest income	54	57
Interest expense	(130)	(119)
Net interest income	(76)	(62)
Trading revenue (expense)	(2,020)	(778)
Servicing and other fees from HSBC affiliates:
Gain on instruments designated at fair value and related derivatives	125	432
Support services from HSBC affiliates:
Total support services from HSBC affiliates	(399)	(384)
Rental income from HSBC affiliates, net	14	9
Stock based compensation expense	(9)	(5)
HSBC Markets (USA) Inc. ("HMUS")
Support services from HSBC affiliates:
Total support services from HSBC affiliates	(56)	(53)
Other HSBC affiliates
Support services from HSBC affiliates:
Total support services from HSBC affiliates	(108)	(111)
HSBC Technology & Services (USA) Inc. ("HTSU")
Support services from HSBC affiliates:
Total support services from HSBC affiliates	(235)	(220)
Servicing and other fees from HSBC affiliates
Servicing and other fees from HSBC affiliates:
Other revenues	88	74
Servicing and other fees from HSBC affiliates | Related Party
Servicing and other fees from HSBC affiliates:
Other revenues	88	74
Servicing and other fees from HSBC affiliates | HSBC Bank plc
Servicing and other fees from HSBC affiliates:
Other revenues	48	41
Servicing and other fees from HSBC affiliates | HSBC Markets (USA) Inc. ("HMUS")
Servicing and other fees from HSBC affiliates:
Other revenues	23	18
Servicing and other fees from HSBC affiliates | Other HSBC affiliates
Servicing and other fees from HSBC affiliates:
Other revenues	$ 17	$ 15