Long-Term Debt-Schedule (Details) - USD ($) $ in Millions	Dec. 31, 2019	Dec. 31, 2018
Debt Instrument [Line Items]
Long-term debt	$ 26,697	$ 30,628
HSBC USA Inc [Member]
Debt Instrument [Line Items]
Long-term debt	17,443	18,863
Mark-to-market adjustment on fair value option debt	1,195	(243)
HSBC Bank USA and its Subsidiaries [Member]
Debt Instrument [Line Items]
Long-term debt	9,254	11,765
Mark-to-market adjustment on fair value option debt	224	196
Senior debt [Member] \| HSBC USA Inc [Member]
Debt Instrument [Line Items]
Long-term debt	14,226	17,086
Senior debt [Member] \| HSBC Bank USA and its Subsidiaries [Member]
Debt Instrument [Line Items]
Long-term debt	6,345	7,827
Senior debt [Member] \| Fixed Rate Notes [Member] \| HSBC USA Inc [Member]
Debt Instrument [Line Items]
Long-term debt	$ 6,231	7,886
Interest rate, weighted average	3.20%
Senior debt [Member] \| Fixed Rate Notes [Member] \| HSBC USA Inc [Member] \| Minimum [Member]
Debt Instrument [Line Items]
Interest rate, fixed	2.35%
Senior debt [Member] \| Fixed Rate Notes [Member] \| HSBC USA Inc [Member] \| Maximum [Member]
Debt Instrument [Line Items]
Interest rate, fixed	4.20%
Senior debt [Member] \| Fixed Rate Notes [Member] \| HSBC Bank USA and its Subsidiaries [Member]
Debt Instrument [Line Items]
Long-term debt	$ 5,124	4,927
Interest rate, weighted average	3.89%
Senior debt [Member] \| Fixed Rate Notes [Member] \| HSBC Bank USA and its Subsidiaries [Member] \| Minimum [Member]
Debt Instrument [Line Items]
Interest rate, fixed	3.67%
Senior debt [Member] \| Fixed Rate Notes [Member] \| HSBC Bank USA and its Subsidiaries [Member] \| Maximum [Member]
Debt Instrument [Line Items]
Interest rate, fixed	4.37%
Senior debt [Member] \| Floating Rate Notes [Member] \| HSBC USA Inc [Member]
Debt Instrument [Line Items]
Long-term debt	$ 0	350
Senior debt [Member] \| Floating Rate Notes [Member] \| HSBC Bank USA and its Subsidiaries [Member]
Debt Instrument [Line Items]
Long-term debt	$ 29	31
Interest rate, weighted average	1.73%
Senior debt [Member] \| Floating Rate Notes [Member] \| HSBC Bank USA and its Subsidiaries [Member] \| Minimum [Member]
Debt Instrument [Line Items]
Interest rate, floating	1.71%
Senior debt [Member] \| Floating Rate Notes [Member] \| HSBC Bank USA and its Subsidiaries [Member] \| Maximum [Member]
Debt Instrument [Line Items]
Interest rate, floating	1.88%
Senior debt [Member] \| Structured Notes [Member] \| HSBC USA Inc [Member]
Debt Instrument [Line Items]
Long-term debt	$ 7,995	8,850
Interest rate, weighted average	2.49%
Senior debt [Member] \| Structured Notes [Member] \| HSBC USA Inc [Member] \| Minimum [Member]
Debt Instrument [Line Items]
Interest rate, floating	1.74%
Senior debt [Member] \| Structured Notes [Member] \| HSBC USA Inc [Member] \| Maximum [Member]
Debt Instrument [Line Items]
Interest rate, floating	4.21%
Senior debt [Member] \| Structured Notes [Member] \| HSBC Bank USA and its Subsidiaries [Member]
Debt Instrument [Line Items]
Long-term debt	$ 192	769
Interest rate, weighted average	2.93%
Senior debt [Member] \| Structured Notes [Member] \| HSBC Bank USA and its Subsidiaries [Member] \| Minimum [Member]
Debt Instrument [Line Items]
Interest rate, floating	1.76%
Senior debt [Member] \| Structured Notes [Member] \| HSBC Bank USA and its Subsidiaries [Member] \| Maximum [Member]
Debt Instrument [Line Items]
Interest rate, floating	3.04%
Senior debt [Member] \| FHLB Advances - Floating Rate [Member] \| HSBC Bank USA and its Subsidiaries [Member]
Debt Instrument [Line Items]
Long-term debt	$ 1,000	2,100
Interest rate, weighted average	1.97%
Interest rate, floating	1.97%
Subordinated Debt [Member] \| HSBC USA Inc [Member]
Debt Instrument [Line Items]
Long-term debt	$ 2,022	2,020
Subordinated Debt [Member] \| Fixed Rate Notes [Member] \| HSBC USA Inc [Member]
Debt Instrument [Line Items]
Long-term debt	$ 1,172	1,170
Interest rate, weighted average	6.16%
Subordinated Debt [Member] \| Fixed Rate Notes [Member] \| HSBC USA Inc [Member] \| Minimum [Member]
Debt Instrument [Line Items]
Interest rate, fixed	5.00%
Subordinated Debt [Member] \| Fixed Rate Notes [Member] \| HSBC USA Inc [Member] \| Maximum [Member]
Debt Instrument [Line Items]
Interest rate, fixed	9.30%
Subordinated Debt [Member] \| Fixed Rate Notes [Member] \| HSBC Bank USA and its Subsidiaries [Member]
Debt Instrument [Line Items]
Long-term debt	$ 2,685	3,676
Interest rate, weighted average	5.67%
Subordinated Debt [Member] \| Fixed Rate Notes [Member] \| HSBC Bank USA and its Subsidiaries [Member] \| Minimum [Member]
Debt Instrument [Line Items]
Interest rate, fixed	4.88%
Subordinated Debt [Member] \| Fixed Rate Notes [Member] \| HSBC Bank USA and its Subsidiaries [Member] \| Maximum [Member]
Debt Instrument [Line Items]
Interest rate, fixed	7.00%
Subordinated Debt [Member] \| Floating Rate Notes [Member] \| HSBC USA Inc [Member]
Debt Instrument [Line Items]
Long-term debt	$ 850	850
Interest rate, weighted average	4.12%
Interest rate, floating	4.12%
VIE-Issued Fixed Rate Notes [Member] \| Fixed Rate Notes [Member] \| HSBC Bank USA and its Subsidiaries [Member]
Debt Instrument [Line Items]
Long-term debt	$ 0	$ 66

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