Related Party Transactions - Summary of Related Party Transactions (Income - Expense) (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2022	Sep. 30, 2021	Sep. 30, 2022	Sep. 30, 2021
Income (Expense):
Interest income	$ 1,092	$ 658	$ 2,487	$ 2,035
Interest expense	(549)	(138)	(935)	(461)
Net interest income	543	520	1,552	1,574
Trading revenue (expense)	163	(42)	296	1
Servicing and other fees from HSBC affiliates:
Gain (loss) on instruments designated at fair value and related derivatives	(29)	8	(4)	33
Support services from HSBC affiliates:
Total support services from HSBC affiliates	(419)	(389)	(1,256)	(1,148)
Affiliated Entity
Income (Expense):
Interest income	36	6	58	20
Interest expense	(79)	(52)	(191)	(185)
Net interest income	(43)	(46)	(133)	(165)
Trading revenue (expense)	1,320	(1,116)	3,925	(2,106)
Servicing and other fees from HSBC affiliates:
Gain (loss) on instruments designated at fair value and related derivatives	(337)	(62)	(1,627)	803
Support services from HSBC affiliates:
Total support services from HSBC affiliates	(419)	(389)	(1,256)	(1,148)
Rental income from HSBC affiliates, net	10	12	29	32
Stock based compensation expense	(3)	(1)	(10)	(12)
HSBC Markets (USA) Inc. (HMUS) and subsidiaries [Member]
Support services from HSBC affiliates:
Total support services from HSBC affiliates	(46)	(26)	(129)	(72)
Other HSBC affiliates
Support services from HSBC affiliates:
Total support services from HSBC affiliates	(129)	(121)	(379)	(322)
HSBC Technology and Services (USA) (HTSU) [Member]
Support services from HSBC affiliates:
Total support services from HSBC affiliates	(244)	(242)	(748)	(754)
Servicing and other fees from HSBC affiliates
Servicing and other fees from HSBC affiliates:
Other revenues	77	79	265	232
Servicing and other fees from HSBC affiliates | Affiliated Entity
Servicing and other fees from HSBC affiliates:
Other revenues	77	79	265	232
Servicing and other fees from HSBC affiliates | HSBC Bank plc [Member]
Servicing and other fees from HSBC affiliates:
Other revenues	43	44	151	124
Servicing and other fees from HSBC affiliates | HSBC Markets (USA) Inc. (HMUS) and subsidiaries [Member]
Servicing and other fees from HSBC affiliates:
Other revenues	15	22	57	70
Servicing and other fees from HSBC affiliates | Other HSBC affiliates
Servicing and other fees from HSBC affiliates:
Other revenues	$ 19	$ 13	$ 57	$ 38