Long-Term Debt-Schedule (Details) - USD ($) $ in Millions	Dec. 31, 2017	Dec. 31, 2016
Debt Instrument [Line Items]
Long-term debt	$ 34,966	$ 37,739
HSBC USA Inc [Member]
Debt Instrument [Line Items]
Long-term debt	23,316	23,378
Mark-to-market adjustment on fair value option debt	1,125	337
HSBC Bank USA and its Subsidiaries [Member]
Debt Instrument [Line Items]
Long-term debt	11,650	14,361
Mark-to-market adjustment on fair value option debt	481	230
Senior debt [Member] | HSBC USA Inc [Member]
Debt Instrument [Line Items]
Long-term debt	20,171	21,020
Senior debt [Member] | HSBC Bank USA and its Subsidiaries [Member]
Debt Instrument [Line Items]
Long-term debt	7,524	9,949
Senior debt [Member] | Fixed Rate Notes [Member] | HSBC USA Inc [Member]
Debt Instrument [Line Items]
Long-term debt	$ 10,185	11,423
Interest rate, weighted average	2.30%
Senior debt [Member] | Fixed Rate Notes [Member] | HSBC USA Inc [Member] | Minimum [Member]
Debt Instrument [Line Items]
Interest rate, fixed	1.63%
Senior debt [Member] | Fixed Rate Notes [Member] | HSBC USA Inc [Member] | Maximum [Member]
Debt Instrument [Line Items]
Interest rate, fixed	3.50%
Senior debt [Member] | Floating Rate Notes [Member] | HSBC USA Inc [Member]
Debt Instrument [Line Items]
Long-term debt	$ 849	1,748
Interest rate, weighted average	2.22%
Senior debt [Member] | Floating Rate Notes [Member] | HSBC USA Inc [Member] | Minimum [Member]
Debt Instrument [Line Items]
Interest rate, floating	2.02%
Senior debt [Member] | Floating Rate Notes [Member] | HSBC USA Inc [Member] | Maximum [Member]
Debt Instrument [Line Items]
Interest rate, floating	2.55%
Senior debt [Member] | Floating Rate Notes [Member] | HSBC Bank USA and its Subsidiaries [Member]
Debt Instrument [Line Items]
Long-term debt	$ 4,031	4,031
Interest rate, weighted average	2.88%
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	3.13%
Senior debt [Member] | Structured Notes [Member] | HSBC USA Inc [Member]
Debt Instrument [Line Items]
Long-term debt	$ 9,137	7,849
Interest rate, weighted average	2.38%
Senior debt [Member] | Structured Notes [Member] | HSBC USA Inc [Member] | Minimum [Member]
Debt Instrument [Line Items]
Interest rate, floating	1.54%
Senior debt [Member] | Structured Notes [Member] | HSBC USA Inc [Member] | Maximum [Member]
Debt Instrument [Line Items]
Interest rate, floating	3.99%
Senior debt [Member] | Structured Notes [Member] | HSBC Bank USA and its Subsidiaries [Member]
Debt Instrument [Line Items]
Long-term debt	$ 393	218
Interest rate, weighted average	1.98%
Senior debt [Member] | Structured Notes [Member] | HSBC Bank USA and its Subsidiaries [Member] | Minimum [Member]
Debt Instrument [Line Items]
Interest rate, floating	1.54%
Senior debt [Member] | Structured Notes [Member] | HSBC Bank USA and its Subsidiaries [Member] | Maximum [Member]
Debt Instrument [Line Items]
Interest rate, floating	4.74%
Senior debt [Member] | FHLB Advances - Floating Rate [Member] | HSBC Bank USA and its Subsidiaries [Member]
Debt Instrument [Line Items]
Long-term debt	$ 3,100	5,700
Interest rate, weighted average	1.84%
Senior debt [Member] | FHLB Advances - Floating Rate [Member] | HSBC Bank USA and its Subsidiaries [Member] | Minimum [Member]
Debt Instrument [Line Items]
Interest rate, floating	1.42%
Senior debt [Member] | FHLB Advances - Floating Rate [Member] | HSBC Bank USA and its Subsidiaries [Member] | Maximum [Member]
Debt Instrument [Line Items]
Interest rate, floating	2.18%
Subordinated Debt [Member] | HSBC USA Inc [Member]
Debt Instrument [Line Items]
Long-term debt	$ 2,020	2,021
Subordinated Debt [Member] | Fixed Rate Notes [Member] | HSBC USA Inc [Member]
Debt Instrument [Line Items]
Long-term debt	$ 1,170	1,171
Interest rate, weighted average	6.15%
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	$ 3,572	4,103
Interest rate, weighted average	5.90%
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%
VIE-Issued Fixed Rate Notes [Member] | Fixed Rate Notes [Member] | HSBC Bank USA and its Subsidiaries [Member]
Debt Instrument [Line Items]
Long-term debt	$ 73	$ 79
Interest rate, weighted average	17.20%
Interest rate, fixed	17.20%