Retained Earnings and Regulatory Capital Requirements - Capital Amounts and Ratios in Accordance With Current Banking Regulations (Details) - USD ($) $ in Millions		Sep. 30, 2016	Dec. 31, 2015
HSBC USA Inc [Member]
Common equity Tier 1 ratio:
Capital Amount, Common Equity Tier 1		$ 17,939	$ 17,766
Well Capitalized Ratio Common equity Tier 1	[1],[2]	4.50%	4.50%
Actual Ratio Common equity Tier 1		13.50%	12.00%
Tier 1 capital ratio:
Capital Amount, Tier 1 capital		$ 19,003	$ 18,764
Well-Capitalized Ratio, Tier 1 capital	[1]	6.00%	6.00%
Actual Ratio, Tier 1 Capital		14.30%	12.60%
Total capital ratio:
Capital Amount		$ 23,951	$ 24,425
Well-Capitalized Ratio	[1]	10.00%	10.00%
Actual Ratio, Total Capital		18.00%	16.50%
Tier 1 leverage ratio:
Capital Amount, Tier 1 leverage capital		$ 19,003	$ 18,764
Well-Capitalized Ratio, Tier 1 leverage capital	[1],[2]	4.00%	4.00%
Actual Ratio, Tier 1 leverage capital		9.10%	9.50%
Risk weighted assets:
Risk Weighted Assets		$ 132,885	$ 148,421
HSBC Bank USA, National Association [Member]
Common equity Tier 1 ratio:
Capital Amount, Common Equity Tier 1		$ 19,980	$ 19,796
Well Capitalized Ratio Common equity Tier 1	[1]	6.50%	6.50%
Actual Ratio Common equity Tier 1		15.60%	13.80%
Tier 1 capital ratio:
Capital Amount, Tier 1 capital		$ 22,334	$ 22,109
Well-Capitalized Ratio, Tier 1 capital	[1]	8.00%	8.00%
Actual Ratio, Tier 1 Capital		17.40%	15.40%
Total capital ratio:
Capital Amount		$ 26,715	$ 26,670
Well-Capitalized Ratio	[1]	10.00%	10.00%
Actual Ratio, Total Capital		20.80%	18.60%
Tier 1 leverage ratio:
Capital Amount, Tier 1 leverage capital		$ 22,334	$ 22,109
Well-Capitalized Ratio, Tier 1 leverage capital	[1]	5.00%	5.00%
Actual Ratio, Tier 1 leverage capital		11.00%	11.60%
Risk weighted assets:
Risk Weighted Assets		$ 128,290	$ 143,393

[1] HSBC USA and HSBC Bank USA are categorized as "well-capitalized," as defined by their principal regulators. To be categorized as well-capitalized under regulatory guidelines, a banking institution must have the ratios reflected in the above table, and must not be subject to a directive, order, or written agreement to meet and maintain specific capital levels.

[2] There are no common equity Tier 1 or Tier 1 leverage ratio components in the definition of a well-capitalized bank holding company. The ratios shown are the regulatory minimum ratios.