Financial Statements of HSBC USA Inc. (Parent) Statement of Comprehensive Income(Loss) (Details) - USD ($) $ in Millions	3 Months Ended								12 Months Ended
	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Condensed Financial Statements, Captions [Line Items]
Net income (loss)	$ 133	$ (250)	$ 121	$ 109	$ 112	$ 177	$ 269	$ (238)	$ 113	$ 320	$ (179)
Net change in unrealized gains (losses), net of tax:
Investment securities									403	(220)	211
Fair value option liabilities attributable to our own credit spread									(310)	324	(193)
Derivatives designated as cash flow hedges									8
Derivatives designated as cash flow hedges										40	(7)
Pension and post-retirement benefit plans									(14)	8	2
Total other comprehensive income									87	152	13
Comprehensive income (loss)									200	472	(166)
HSBC USA Inc [Member]
Condensed Financial Statements, Captions [Line Items]
Net income (loss)									113	320	(179)
Net change in unrealized gains (losses), net of tax:
Investment securities									403	(220)	211
Fair value option liabilities attributable to our own credit spread									(310)	324	(193)
Derivatives designated as cash flow hedges									8
Derivatives designated as cash flow hedges										40	(7)
Pension and post-retirement benefit plans									(14)	8	2
Total other comprehensive income									87	152	13
Comprehensive income (loss)									$ 200	$ 472	$ (166)