Related Party Transactions - Summary of Related Party Transactions (Income - Expense) (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2022	Jun. 30, 2021	Jun. 30, 2022	Jun. 30, 2021
Income (Expense):
Interest income	$ 783	$ 676	$ 1,395	$ 1,377
Interest expense	(251)	(153)	(386)	(323)
Net interest income	532	523	1,009	1,054
Trading revenue (expense)	61	2	133	43
Servicing and other fees from HSBC affiliates:
Gain (loss) on instruments designated at fair value and related derivatives	19	7	25	25
Support services from HSBC affiliates:
Total support services from HSBC affiliates	(419)	(392)	(837)	(759)
Affiliated Entity
Income (Expense):
Interest income	16	7	22	14
Interest expense	(60)	(60)	(112)	(133)
Net interest income	(44)	(53)	(90)	(119)
Trading revenue (expense)	1,330	(1,121)	2,605	(990)
Servicing and other fees from HSBC affiliates:
Gain (loss) on instruments designated at fair value and related derivatives	(894)	397	(1,290)	865
Support services from HSBC affiliates:
Total support services from HSBC affiliates	(419)	(392)	(837)	(759)
Rental income from HSBC affiliates, net	9	7	19	20
Stock based compensation expense	(3)	(5)	(7)	(11)
HSBC Markets (USA) Inc. (HMUS) and subsidiaries [Member]
Support services from HSBC affiliates:
Total support services from HSBC affiliates	(46)	(18)	(83)	(46)
Other HSBC affiliates
Support services from HSBC affiliates:
Total support services from HSBC affiliates	(129)	(106)	(250)	(201)
HSBC Technology and Services (USA) (HTSU) [Member]
Support services from HSBC affiliates:
Total support services from HSBC affiliates	(244)	(268)	(504)	(512)
Servicing and other fees from HSBC affiliates
Servicing and other fees from HSBC affiliates:
Other revenues	87	70	188	153
Servicing and other fees from HSBC affiliates | Affiliated Entity
Servicing and other fees from HSBC affiliates:
Other revenues	87	70	188	153
Servicing and other fees from HSBC affiliates | HSBC Bank plc [Member]
Servicing and other fees from HSBC affiliates:
Other revenues	48	32	108	80
Servicing and other fees from HSBC affiliates | HSBC Markets (USA) Inc. (HMUS) and subsidiaries [Member]
Servicing and other fees from HSBC affiliates:
Other revenues	17	26	42	48
Servicing and other fees from HSBC affiliates | Other HSBC affiliates
Servicing and other fees from HSBC affiliates:
Other revenues	$ 22	$ 12	$ 38	$ 25