Financial Statements of HSBC USA Inc. (Parent) Statement of Income (Loss) (Details) - USD ($) $ in Millions	3 Months Ended								12 Months Ended
	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Income:
Other interest income									$ 52	$ 43	$ 59
Other securities gains, net									52	70	48
Total income									4,440	3,516	3,844
Expenses:
Other Interest Expense									25	15	16
Income before income tax	$ 134	$ 155	$ 312	$ 448	$ (48)	$ 59	$ (26)	$ 233	1,049	218	560
Income tax expense	907	61	108	152	(11)	26	(5)	79	1,228	89	230
Net income (loss)	$ (773)	$ 94	$ 204	$ 296	$ (37)	$ 33	$ (21)	$ 154	(179)	129	330
HSBC USA Inc [Member]
Income:
Dividends from banking subsidiaries									136	136	104
Dividends from other subsidiaries									0	17	1
Interest from subsidiaries									309	268	97
Interest from other HSBC affiliates									37	115	121
Other interest income									5	2	14
Other securities gains, net									0	7	1
Other income from subsidiaries									(1)	1	(2)
Other income from other HSBC Affiliates									1,093	418	(79)
Other income (loss)									(772)	(321)	121
Total income									807	643	378
Expenses:
Interest to subsidiaries									0	0	23
Interest to other HSBC Affiliates									40	43	28
Other Interest Expense									541	475	375
Other expenses with subsidiaries									15	27	0
Other expenses									3	3	6
Total expenses									599	548	432
Income before income tax									208	95	(54)
Income tax expense									18	(27)	(76)
Income (loss) before equity in undistributed income (loss) of subsidiaries									190	122	22
Equity in undistributed income (loss) of subsidiaries									(369)	7	308
Net income (loss)									$ (179)	$ 129	$ 330