Long-Term Debt-Schedule (Details) - USD ($) $ in Millions	Dec. 31, 2018	Dec. 31, 2017
Debt Instrument [Line Items]
Long-term debt	$ 30,628	$ 34,966
HSBC USA Inc [Member]
Debt Instrument [Line Items]
Long-term debt	18,863	23,316
Mark-to-market adjustment on fair value option debt	(243)	1,125
HSBC Bank USA and its Subsidiaries [Member]
Debt Instrument [Line Items]
Long-term debt	11,765	11,650
Mark-to-market adjustment on fair value option debt	196	481
Senior debt [Member] | HSBC USA Inc [Member]
Debt Instrument [Line Items]
Long-term debt	17,086	20,171
Senior debt [Member] | HSBC Bank USA and its Subsidiaries [Member]
Debt Instrument [Line Items]
Long-term debt	7,827	7,524
Senior debt [Member] | Fixed Rate Notes [Member] | HSBC USA Inc [Member]
Debt Instrument [Line Items]
Long-term debt	$ 7,886	10,185
Interest rate, weighted average	3.01%
Senior debt [Member] | Fixed Rate Notes [Member] | HSBC USA Inc [Member] | Minimum [Member]
Debt Instrument [Line Items]
Interest rate, fixed	2.25%
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	$ 4,927	0
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	$ 350	849
Interest rate, weighted average	3.24%
Interest rate, floating	3.24%
Senior debt [Member] | Floating Rate Notes [Member] | HSBC Bank USA and its Subsidiaries [Member]
Debt Instrument [Line Items]
Long-term debt	$ 31	4,031
Interest rate, weighted average	1.33%
Senior debt [Member] | Floating Rate Notes [Member] | HSBC Bank USA and its Subsidiaries [Member] | Minimum [Member]
Debt Instrument [Line Items]
Interest rate, floating	0.93%
Senior debt [Member] | Floating Rate Notes [Member] | HSBC Bank USA and its Subsidiaries [Member] | Maximum [Member]
Debt Instrument [Line Items]
Interest rate, floating	1.38%
Senior debt [Member] | Structured Notes [Member] | HSBC USA Inc [Member]
Debt Instrument [Line Items]
Long-term debt	$ 8,850	9,137
Interest rate, weighted average	3.41%
Senior debt [Member] | Structured Notes [Member] | HSBC USA Inc [Member] | Minimum [Member]
Debt Instrument [Line Items]
Interest rate, floating	2.40%
Senior debt [Member] | Structured Notes [Member] | HSBC USA Inc [Member] | Maximum [Member]
Debt Instrument [Line Items]
Interest rate, floating	5.11%
Senior debt [Member] | Structured Notes [Member] | HSBC Bank USA and its Subsidiaries [Member]
Debt Instrument [Line Items]
Long-term debt	$ 769	393
Interest rate, weighted average	5.85%
Senior debt [Member] | Structured Notes [Member] | HSBC Bank USA and its Subsidiaries [Member] | Minimum [Member]
Debt Instrument [Line Items]
Interest rate, floating	2.69%
Senior debt [Member] | Structured Notes [Member] | HSBC Bank USA and its Subsidiaries [Member] | Maximum [Member]
Debt Instrument [Line Items]
Interest rate, floating	9.07%
Senior debt [Member] | FHLB Advances - Floating Rate [Member] | HSBC Bank USA and its Subsidiaries [Member]
Debt Instrument [Line Items]
Long-term debt	$ 2,100	3,100
Interest rate, weighted average	2.88%
Senior debt [Member] | FHLB Advances - Floating Rate [Member] | HSBC Bank USA and its Subsidiaries [Member] | Minimum [Member]
Debt Instrument [Line Items]
Interest rate, floating	2.50%
Senior debt [Member] | FHLB Advances - Floating Rate [Member] | HSBC Bank USA and its Subsidiaries [Member] | Maximum [Member]
Debt Instrument [Line Items]
Interest rate, floating	3.33%
Subordinated Debt [Member] | HSBC USA Inc [Member]
Debt Instrument [Line Items]
Long-term debt	$ 2,020	2,020
Subordinated Debt [Member] | Fixed Rate Notes [Member] | HSBC USA Inc [Member]
Debt Instrument [Line Items]
Long-term debt	$ 1,170	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	$ 3,676	3,572
Interest rate, weighted average	5.70%
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	3.66%
Interest rate, floating	3.66%
VIE-Issued Fixed Rate Notes [Member] | Fixed Rate Notes [Member] | HSBC Bank USA and its Subsidiaries [Member]
Debt Instrument [Line Items]
Long-term debt	$ 66	$ 73
Interest rate, weighted average	17.20%
Interest rate, fixed	17.20%