Retained Earnings and Regulatory Capital Requirements - Capital Amounts and Ratios in Accordance With Current Banking Regulations (Details) $ in Millions	Jun. 30, 2022 USD ($)	Dec. 31, 2021 USD ($)
HSBC USA
Common equity Tier 1 ratio:
Capital Amount	$ 15,729	$ 15,341
Well-Capitalized Ratio	0.045	0.045
Actual Ratio	0.150	0.151
Tier 1 capital ratio:
Capital Amount	$ 16,994	$ 16,606
Well-Capitalized Ratio	0.060	0.060
Actual Ratio	0.162	0.163
Total capital ratio:
Capital Amount	$ 19,255	$ 18,821
Well-Capitalized Ratio	0.100	0.100
Actual Ratio	0.184	0.185
Tier 1 leverage ratio:
Capital Amount	$ 16,994	$ 16,606
Well-Capitalized Ratio	0.040	0.040
Actual Ratio	0.098	0.085
Risk weighted assets:
Capital Amount	$ 104,674	$ 101,827
Adjusted quarterly average assets
Capital Amount	173,191	194,469
HSBC Bank USA
Common equity Tier 1 ratio:
Capital Amount	$ 18,137	$ 17,665
Well-Capitalized Ratio	0.065	0.065
Actual Ratio	0.176	0.176
Tier 1 capital ratio:
Capital Amount	$ 20,637	$ 20,165
Well-Capitalized Ratio	0.080	0.080
Actual Ratio	0.201	0.201
Total capital ratio:
Capital Amount	$ 22,673	$ 22,157
Well-Capitalized Ratio	0.100	0.100
Actual Ratio	0.220	0.221
Tier 1 leverage ratio:
Capital Amount	$ 20,637	$ 20,165
Well-Capitalized Ratio	0.050	0.050
Actual Ratio	0.121	0.105
Risk weighted assets:
Capital Amount	$ 102,877	$ 100,363
Adjusted quarterly average assets
Capital Amount	$ 170,178	$ 192,521