Retained Earnings and Regulatory Capital Requirements - Capital Amounts and Ratios in Accordance With Current Banking Regulations (Details) $ in Millions	Sep. 30, 2024 USD ($)	Dec. 31, 2023 USD ($)
HSBC USA
Common equity Tier 1 ratio:
Capital Amount	$ 13,279	$ 12,822
Well-Capitalized Ratio	0.045	0.045
Actual Ratio	0.130	0.130
Tier 1 capital ratio:
Capital Amount	$ 13,544	$ 13,087
Well-Capitalized Ratio	0.060	0.060
Actual Ratio	0.133	0.133
Total capital ratio:
Capital Amount	$ 15,889	$ 15,452
Well-Capitalized Ratio	0.100	0.100
Actual Ratio	0.155	0.157
Tier 1 leverage ratio:
Capital Amount	$ 13,544	$ 13,087
Well-Capitalized Ratio	0.040	0.040
Actual Ratio	0.082	0.077
Risk weighted assets:
Capital Amount	$ 102,195	$ 98,450
Adjusted quarterly average assets
Capital Amount	166,088	170,527
HSBC Bank USA
Common equity Tier 1 ratio:
Capital Amount	$ 15,527	$ 15,407
Well-Capitalized Ratio	0.065	0.065
Actual Ratio	0.159	0.161
Tier 1 capital ratio:
Capital Amount	$ 17,027	$ 16,907
Well-Capitalized Ratio	0.080	0.080
Actual Ratio	0.175	0.177
Total capital ratio:
Capital Amount	$ 19,077	$ 19,024
Well-Capitalized Ratio	0.100	0.100
Actual Ratio	0.196	0.199
Tier 1 leverage ratio:
Capital Amount	$ 17,027	$ 16,907
Well-Capitalized Ratio	0.050	0.050
Actual Ratio	0.105	0.102
Risk weighted assets:
Capital Amount	$ 97,500	$ 95,455
Adjusted quarterly average assets
Capital Amount	$ 161,401	$ 166,526