Pensions and Other Postretirement Benefits-Assumptions (Details)	6 Months Ended	12 Months Ended
	Jun. 30, 2020	Dec. 31, 2020		Dec. 31, 2019		Dec. 31, 2018
HSBC North America Pension Plan [Member]
Net Benefit Cost [Abstract]
Discount rate		2.45%		3.15%		4.25%
Expected long-term rate of return on Plan assets	5.00%	3.50%	[1]	5.00%	[1]	5.50%	[1]
Postretirement Plans Other Than Pensions [Member]
Projected Benefit Obligation [Abstract]
Discount rate		2.25%		3.00%		4.15%
Salary increase assumption		3.00%		3.00%		3.00%
Net Benefit Cost [Abstract]
Discount rate		3.00%		4.15%		3.45%
Salary increase assumption		3.00%		3.00%		3.00%

[1] As a result of a significant decrease in yields on fixed income securities driven by the COVID-19 pandemic and subsequent reduction in longer term capital market returns, as well as a shift in investment mix that reduced the Plan's exposure to equity investments, HSBC North America decided to reduce its expected long-term rate of return on Plan assets assumption to 3.50 percent, effective beginning July 1, 2020. The expected long-term rate of return on Plan assets used during the first half of 2020 was 5.00 percent