Retained Earnings and Regulatory Capital Requirements - Capital Amounts and Ratios in Accordance With Current Banking Regulations (Details) $ in Millions	Sep. 30, 2022 USD ($)	Dec. 31, 2021 USD ($)
HSBC USA
Common equity Tier 1 ratio:
Capital Amount	$ 14,892	$ 15,341
Well-Capitalized Ratio	0.045	0.045
Actual Ratio	0.140	0.151
Tier 1 capital ratio:
Capital Amount	$ 16,157	$ 16,606
Well-Capitalized Ratio	0.060	0.060
Actual Ratio	0.152	0.163
Total capital ratio:
Capital Amount	$ 18,471	$ 18,821
Well-Capitalized Ratio	0.100	0.100
Actual Ratio	0.173	0.185
Tier 1 leverage ratio:
Capital Amount	$ 16,157	$ 16,606
Well-Capitalized Ratio	0.040	0.040
Actual Ratio	0.095	0.085
Risk weighted assets:
Capital Amount	$ 106,582	$ 101,827
Adjusted quarterly average assets
Capital Amount	169,575	194,469
HSBC Bank USA
Common equity Tier 1 ratio:
Capital Amount	$ 17,334	$ 17,665
Well-Capitalized Ratio	0.065	0.065
Actual Ratio	0.166	0.176
Tier 1 capital ratio:
Capital Amount	$ 19,834	$ 20,165
Well-Capitalized Ratio	0.080	0.080
Actual Ratio	0.190	0.201
Total capital ratio:
Capital Amount	$ 21,915	$ 22,157
Well-Capitalized Ratio	0.100	0.100
Actual Ratio	0.210	0.221
Tier 1 leverage ratio:
Capital Amount	$ 19,834	$ 20,165
Well-Capitalized Ratio	0.050	0.050
Actual Ratio	0.119	0.105
Risk weighted assets:
Capital Amount	$ 104,294	$ 100,363
Adjusted quarterly average assets
Capital Amount	$ 166,258	$ 192,521