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Pensions and Other Postretirement Benefits-Assumptions (Details)
3 Months Ended 6 Months Ended 12 Months Ended
Dec. 31, 2021
Sep. 30, 2021
Jun. 30, 2021
Mar. 31, 2021
Dec. 31, 2020
Sep. 30, 2020
Jun. 30, 2020
Mar. 31, 2020
Dec. 31, 2019
Sep. 30, 2019
Jun. 30, 2019
Mar. 31, 2019
Jun. 30, 2020
Dec. 31, 2021
Dec. 31, 2020
Dec. 31, 2019
HSBC North America Pension Plan                                
Net Benefit Cost [Abstract]                                
Discount rate 2.80% 2.70% 3.10% 2.45% 2.55% 2.70% 3.20% 3.15% 3.15% 3.55% 3.85% 4.25%        
Expected long-term rate of return on Plan assets                         5.00% 3.50% 3.50% 5.00%
Postretirement Plans Other Than Pensions                                
Projected Benefit Obligation [Abstract]                                
Discount rate 2.70%       2.25%       3.00%         2.70% 2.25% 3.00%
Salary increase assumption 3.00%       3.00%       3.00%         3.00% 3.00% 3.00%