Retained Earnings and Regulatory Capital Requirements - Capital Amounts and Ratios in Accordance With Current Banking Regulations (Details) $ in Millions	Dec. 31, 2023 USD ($)	Dec. 31, 2022 USD ($)
HSBC USA
Common equity Tier 1 ratio:
Capital Amount	$ 12,822	$ 13,950
Well-Capitalized Ratio	0.045	0.045
Actual Ratio	0.130	0.135
Tier 1 capital ratio:
Capital Amount	$ 13,087	$ 14,215
Well-Capitalized Ratio	0.060	0.060
Actual Ratio	0.133	0.138
Total capital ratio:
Capital Amount	$ 15,452	$ 16,579
Well-Capitalized Ratio	0.100	0.100
Actual Ratio	0.157	0.161
Tier 1 leverage ratio:
Capital Amount	$ 13,087	$ 14,215
Well-Capitalized Ratio	0.040	0.040
Actual Ratio	0.077	0.085
Risk weighted assets:
Capital Amount	$ 98,450	$ 103,101
Adjusted quarterly average assets
Capital Amount	170,527	167,866
HSBC Bank USA
Common equity Tier 1 ratio:
Capital Amount	$ 15,407	$ 16,492
Well-Capitalized Ratio	0.065	0.065
Actual Ratio	0.161	0.163
Tier 1 capital ratio:
Capital Amount	$ 16,907	$ 17,992
Well-Capitalized Ratio	0.080	0.080
Actual Ratio	0.177	0.178
Total capital ratio:
Capital Amount	$ 19,024	$ 20,114
Well-Capitalized Ratio	0.100	0.100
Actual Ratio	0.199	0.199
Tier 1 leverage ratio:
Capital Amount	$ 16,907	$ 17,992
Well-Capitalized Ratio	0.050	0.050
Actual Ratio	0.102	0.109
Risk weighted assets:
Capital Amount	$ 95,455	$ 101,331
Adjusted quarterly average assets
Capital Amount	$ 166,526	$ 164,564