Retained Earnings and Regulatory Capital Requirements - Capital Amounts and Ratios in Accordance With Current Banking Regulations (Details) - HSBC USA $ in Millions	Dec. 31, 2021 USD ($)	Dec. 31, 2020 USD ($)
Common equity Tier 1 ratio:
Capital Amount, Common equity Tier 1	$ 15,341	$ 15,891
Well-Capitalized Ratio, Common equity Tier 1	0.045	0.045
Actual Ratio, Common equity Tier 1	0.151	0.145
Tier 1 capital ratio:
Capital Amount, Tier 1 capital	$ 16,606	$ 17,156
Well-Capitalized Ratio, Tier 1 capital	0.060	0.060
Actual Ratio, Tier 1 capital	0.163	0.156
Total capital ratio:
Capital Amount, Total capital	$ 18,821	$ 20,680
Well-Capitalized Ratio, Total capital	0.100	0.100
Actual Ratio, Total capital	0.185	0.188
Tier 1 leverage ratio:
Capital Amount, Tier 1 leverage capital	$ 16,606	$ 17,156
Well-Capitalized Ratio, Tier 1 leverage capital	0.040	0.040
Actual Ratio, Tier 1 leverage capital	0.085	0.086
Supplementary leverage ratio ("SLR"):
Capital Amount, Supplementary Leverage Ratio	$ 16,606	$ 17,156
Well-Capitalized Ratio, Supplementary Leverage Ratio	0.030	0.030
Actual Ratio, Supplementary Leverage Ratio	0.066	0.078
Risk weighted assets:
Banking Regulation, Risk-Weighted Assets, Actual	$ 101,827	$ 109,809
Adjusted quarterly average assets
Adjusted quarterly average assets	194,469	198,698
Total leverage exposure
Total leverage exposure	251,531	$ 221,216
As Previously Reported
Common equity Tier 1 ratio:
Actual Ratio, Common equity Tier 1		0.147
Tier 1 capital ratio:
Actual Ratio, Tier 1 capital		0.159
Total capital ratio:
Actual Ratio, Total capital		0.192
Risk weighted assets:
Banking Regulation, Risk-Weighted Assets, Actual		$ 107,808
Capital Amount, Common equity Tier 1	$ 17,665	$ 18,180
Well-Capitalized Ratio, Common equity Tier 1	0.065	0.065
Actual Ratio, Common equity Tier 1	0.176	0.164
Capital Amount, Tier 1 capital	$ 20,165	$ 20,680
Well-Capitalized Ratio, Tier 1 capital	0.080	0.080
Actual Ratio, Tier 1 capital	0.201	0.187
Capital Amount, Total capital	$ 22,157	$ 23,303
Well-Capitalized Ratio, Total capital	0.100	0.100
Actual Ratio, Total capital	0.221	0.211
Capital Amount, Tier 1 leverage capital	$ 20,165	$ 20,680
Well-Capitalized Ratio, Tier 1 leverage capital	0.050	0.050
Actual Ratio, Tier 1 leverage capital	0.105	0.103
Capital Amount, Supplementary Leverage Ratio	$ 20,165	$ 20,680
Well-Capitalized Ratio, Supplementary Leverage Ratio	0.030	0.030
Actual Ratio, Supplementary Leverage Ratio	0.081	0.093
Banking Regulation, Risk-Weighted Assets, Actual	$ 100,363	$ 110,682
Adjusted quarterly average assets
Adjusted quarterly average assets	192,521	200,026
Total leverage exposure
Total leverage exposure	$ 248,584	$ 221,334
As Previously Reported
Common equity Tier 1 ratio:
Actual Ratio, Common equity Tier 1		0.172
Tier 1 capital ratio:
Actual Ratio, Tier 1 capital		0.196
Total capital ratio:
Actual Ratio, Total capital		0.220
Risk weighted assets:
Banking Regulation, Risk-Weighted Assets, Actual		$ 105,681