Long-Term Debt-Schedule (Details) - USD ($) $ in Millions	Dec. 31, 2020	Dec. 31, 2019
Debt Instrument [Line Items]
Long-term debt	$ 19,979	$ 26,697
HSBC USA Inc [Member]
Debt Instrument [Line Items]
Long-term debt	13,544	17,443
Mark-to-market adjustment on fair value option debt	1,344	1,195
HSBC Bank USA and its Subsidiaries [Member]
Debt Instrument [Line Items]
Long-term debt	6,435	9,254
Mark-to-market adjustment on fair value option debt	308	224
Senior debt [Member] \| HSBC USA Inc [Member]
Debt Instrument [Line Items]
Long-term debt	10,928	14,226
Senior debt [Member] \| HSBC Bank USA and its Subsidiaries [Member]
Debt Instrument [Line Items]
Long-term debt	4,686	6,345
Senior debt [Member] \| Fixed Rate Notes [Member] \| HSBC USA Inc [Member]
Debt Instrument [Line Items]
Long-term debt	$ 2,990	6,231
Interest rate, weighted average	4.01%
Senior debt [Member] \| Fixed Rate Notes [Member] \| HSBC USA Inc [Member] \| Minimum [Member]
Debt Instrument [Line Items]
Interest rate, fixed	3.50%
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	$ 0	5,124
Senior debt [Member] \| Floating Rate Notes [Member] \| HSBC Bank USA and its Subsidiaries [Member]
Debt Instrument [Line Items]
Long-term debt	$ 42	29
Interest rate, weighted average	0.39%
Senior debt [Member] \| Floating Rate Notes [Member] \| HSBC Bank USA and its Subsidiaries [Member] \| Minimum [Member]
Debt Instrument [Line Items]
Interest rate, floating	0.03%
Senior debt [Member] \| Floating Rate Notes [Member] \| HSBC Bank USA and its Subsidiaries [Member] \| Maximum [Member]
Debt Instrument [Line Items]
Interest rate, floating	0.94%
Senior debt [Member] \| Structured Notes [Member] \| HSBC USA Inc [Member]
Debt Instrument [Line Items]
Long-term debt	$ 7,938	7,995
Interest rate, weighted average	0.76%
Senior debt [Member] \| Structured Notes [Member] \| HSBC USA Inc [Member] \| Minimum [Member]
Debt Instrument [Line Items]
Interest rate, floating	0.15%
Senior debt [Member] \| Structured Notes [Member] \| HSBC USA Inc [Member] \| Maximum [Member]
Debt Instrument [Line Items]
Interest rate, floating	2.54%
Senior debt [Member] \| Structured Notes [Member] \| HSBC Bank USA and its Subsidiaries [Member]
Debt Instrument [Line Items]
Long-term debt	$ 394	192
Interest rate, weighted average	1.14%
Senior debt [Member] \| Structured Notes [Member] \| HSBC Bank USA and its Subsidiaries [Member] \| Minimum [Member]
Debt Instrument [Line Items]
Interest rate, floating	(0.55%)
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 - Fixed Rate [Member] \| HSBC Bank USA and its Subsidiaries [Member]
Debt Instrument [Line Items]
Long-term debt	$ 3,250	0
Interest rate, weighted average	0.92%
Senior debt [Member] \| FHLB Advances - Fixed Rate [Member] \| HSBC Bank USA and its Subsidiaries [Member] \| Minimum [Member]
Debt Instrument [Line Items]
Interest rate, fixed	0.80%
Senior debt [Member] \| FHLB Advances - Fixed Rate [Member] \| HSBC Bank USA and its Subsidiaries [Member] \| Maximum [Member]
Debt Instrument [Line Items]
Interest rate, fixed	1.12%
Senior debt [Member] \| FHLB Advances - Floating Rate [Member] \| HSBC Bank USA and its Subsidiaries [Member]
Debt Instrument [Line Items]
Long-term debt	$ 1,000	1,000
Interest rate, weighted average	0.30%
Interest rate, floating	0.30%
Subordinated Debt [Member] \| HSBC USA Inc [Member]
Debt Instrument [Line Items]
Long-term debt	$ 1,272	2,022
Subordinated Debt [Member] \| Fixed Rate Notes [Member] \| HSBC USA Inc [Member]
Debt Instrument [Line Items]
Long-term debt	$ 422	1,172
Interest rate, weighted average	8.09%
Subordinated Debt [Member] \| Fixed Rate Notes [Member] \| HSBC USA Inc [Member] \| Minimum [Member]
Debt Instrument [Line Items]
Interest rate, fixed	7.20%
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	$ 1,441	2,685
Interest rate, weighted average	6.36%
Subordinated Debt [Member] \| Fixed Rate Notes [Member] \| HSBC Bank USA and its Subsidiaries [Member] \| Minimum [Member]
Debt Instrument [Line Items]
Interest rate, fixed	5.63%
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	2.43%
Interest rate, floating	2.43%

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Amount, after unamortized (discount) premium and debt issuance costs, of long-term debt. Includes, but not limited to, notes payable, bonds payable, debentures, mortgage loans and commercial paper. Excludes capital lease obligations.

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The interest rate applicable to the portion of the carrying amount of long-term borrowings outstanding as of the balance sheet date, including current maturities, which accrues interest at a set, unchanging rate.

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