Retained Earnings and Regulatory Capital Requirements - Capital Amounts and Ratios in Accordance With Current Banking Regulations (Details) - HSBC USA $ in Millions	Mar. 31, 2022 USD ($)	Dec. 31, 2021 USD ($)
Common equity Tier 1 ratio:
Capital Amount	$ 15,680	$ 15,341
Well-Capitalized Ratio	0.045	0.045
Actual Ratio	0.151	0.151
Tier 1 capital ratio:
Capital Amount	$ 16,945	$ 16,606
Well-Capitalized Ratio	0.060	0.060
Actual Ratio	0.163	0.163
Total capital ratio:
Capital Amount	$ 19,162	$ 18,821
Well-Capitalized Ratio	0.100	0.100
Actual Ratio	0.185	0.185
Tier 1 leverage ratio:
Capital Amount	$ 16,945	$ 16,606
Well-Capitalized Ratio	0.040	0.040
Actual Ratio	0.092	0.085
Risk weighted assets:
Capital Amount	$ 103,826	$ 101,827
Adjusted quarterly average assets
Capital Amount	183,389	194,469
Capital Amount	$ 18,010	$ 17,665
Well-Capitalized Ratio	0.065	0.065
Actual Ratio	0.177	0.176
Capital Amount	$ 20,510	$ 20,165
Well-Capitalized Ratio	0.080	0.080
Actual Ratio	0.201	0.201
Capital Amount	$ 22,502	$ 22,157
Well-Capitalized Ratio	0.100	0.100
Actual Ratio	0.221	0.221
Capital Amount	$ 20,510	$ 20,165
Well-Capitalized Ratio	0.050	0.050
Actual Ratio	0.113	0.105
Capital Amount	$ 101,991	$ 100,363
Capital Amount	$ 181,194	$ 192,521