Retained Earnings and Regulatory Capital Requirements - Capital Amounts and Ratios in Accordance With Current Banking Regulations (Details) $ in Millions	Mar. 31, 2024 USD ($)	Dec. 31, 2023 USD ($)
HSBC USA
Common equity Tier 1 ratio:
Capital Amount	$ 13,036	$ 12,822
Well-Capitalized Ratio	0.045	0.045
Actual Ratio	0.131	0.130
Tier 1 capital ratio:
Capital Amount	$ 13,301	$ 13,087
Well-Capitalized Ratio	0.060	0.060
Actual Ratio	0.134	0.133
Total capital ratio:
Capital Amount	$ 15,650	$ 15,452
Well-Capitalized Ratio	0.100	0.100
Actual Ratio	0.157	0.157
Tier 1 leverage ratio:
Capital Amount	$ 13,301	$ 13,087
Well-Capitalized Ratio	0.040	0.040
Actual Ratio	0.080	0.077
Risk weighted assets:
Capital Amount	$ 99,563	$ 98,450
Adjusted quarterly average assets
Capital Amount	167,189	170,527
HSBC Bank USA
Common equity Tier 1 ratio:
Capital Amount	$ 15,694	$ 15,407
Well-Capitalized Ratio	0.065	0.065
Actual Ratio	0.164	0.161
Tier 1 capital ratio:
Capital Amount	$ 17,194	$ 16,907
Well-Capitalized Ratio	0.080	0.080
Actual Ratio	0.180	0.177
Total capital ratio:
Capital Amount	$ 19,298	$ 19,024
Well-Capitalized Ratio	0.100	0.100
Actual Ratio	0.201	0.199
Tier 1 leverage ratio:
Capital Amount	$ 17,194	$ 16,907
Well-Capitalized Ratio	0.050	0.050
Actual Ratio	0.105	0.102
Risk weighted assets:
Capital Amount	$ 95,788	$ 95,455
Adjusted quarterly average assets
Capital Amount	$ 163,099	$ 166,526