Financial Statements of HSBC USA Inc. (Parent) Statement of Income (Loss) (Details) - USD ($) $ in Millions	3 Months Ended								12 Months Ended
	Dec. 31, 2020	Sep. 30, 2020	Jun. 30, 2020	Mar. 31, 2020	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Income:
Total income									$ 2,899	$ 3,771	$ 4,224
Expenses:
Other Interest Expense									16	35	36
Provision for credit losses	$ (30)	$ (105)	$ 219	$ 726					810	195	(73)
Provision for credit losses					$ (3)	$ 94	$ 46	$ 58	736	195	(73)
Income (loss) before income tax	178	224	56	(1,440)	181	(211)	156	144	(982)	270	586
Income tax expense (benefit)	30	36	49	(157)	48	39	35	35	(42)	157	266
Net income (loss)	$ 148	$ 188	$ 7	$ (1,283)	$ 133	$ (250)	$ 121	$ 109	(940)	113	320
HSBC USA Inc [Member]
Income:
Dividends from banking subsidiaries									121	138	137
Interest from subsidiaries									101	350	367
Interest from other HSBC affiliates									43	91	55
Other income (loss) from subsidiaries									0	2	(2)
Other income (loss) from other HSBC Affiliates									552	1,645	(829)
Other income (loss)									(544)	(1,690)	792
Total income									273	536	520
Expenses:
Interest to subsidiaries									6	0	0
Interest to other HSBC Affiliates									115	140	62
Other Interest Expense									228	549	574
Provision for credit losses									(1)
Provision for credit losses										0	0
Other expenses with subsidiaries									15	12	8
Other expenses									3	5	2
Total expenses									366	706	646
Income (loss) before income tax									(93)	(170)	(126)
Income tax expense (benefit)									(50)	(78)	(66)
Loss before equity in undistributed income (loss) of subsidiaries									(43)	(92)	(60)
Equity in undistributed income (loss) of subsidiaries									(897)	205	380
Net income (loss)									$ (940)	$ 113	$ 320