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Pensions and Other Postretirement Benefits-Assumptions (Details)
12 Months Ended
Dec. 31, 2019
Dec. 31, 2018
Dec. 31, 2017
HSBC North America Pension Plan [Member]      
Net Benefit Cost [Abstract]      
Discount rate 3.15% 4.25% 3.60%
Expected long-term rate of return on Plan assets 5.00% 5.50% 5.50%
Postretirement Plans Other Than Pensions [Member]      
Projected Benefit Obligation [Abstract]      
Discount rate 3.00% 4.15% 3.45%
Salary increase assumption 3.00% 3.00% 3.00%
Net Benefit Cost [Abstract]      
Discount rate 4.15% 3.45% 3.95%
Salary increase assumption 3.00% 3.00% 3.00%