Retained Earnings and Regulatory Capital Requirements - Capital Amounts and Ratios in Accordance With Current Banking Regulations (Details) - USD ($) $ in Millions		Sep. 30, 2015		Dec. 31, 2014
HSBC USA Inc [Member]
Total capital ratio:
Capital Amount	[1]	$ 24,346		$ 21,017
Well-Capitalized Ratio	[1],[2]	10.00%		10.00%
Actual Ratio, Total Capital	[1]	16.33%		15.78%
Tier 1 capital ratio:
Capital Amount, Tier 1 capital	[1]	$ 18,952		$ 15,205
Well-Capitalized Ratio, Tier 1 capital	[2]	6.00%	[3]	6.00%	[1]
Actual Ratio, Tier 1 Capital	[1]	12.71%		11.41%
Common equity Tier 1 ratio:
Capital Amount, Common Equity Tier 1	[1]	$ 17,965		$ 13,754
Well Capitalized Ratio Common equity Tier 1	[1],[2],[3]	4.50%		4.50%
Actual Ratio Common equity Tier 1	[1]	12.05%		10.33%
Tier 1 leverage ratio:
Capital Amount, Tier 1 leverage capital		$ 18,952		$ 15,205
Well-Capitalized Ratio, Tier 1 leverage capital	[2],[3]	4.00%		4.00%
Actual Ratio, Tier 1 leverage capital		9.52%		8.54%
Risk weighted assets:
Risk Weighted Assets	[1]	$ 149,085		$ 133,211
HSBC Bank USA, National Association [Member]
Total capital ratio:
Capital Amount	[1]	$ 26,605		$ 22,760
Well-Capitalized Ratio	[1],[2]	10.00%		10.00%
Actual Ratio, Total Capital	[1]	18.60%		17.86%
Tier 1 capital ratio:
Capital Amount, Tier 1 capital	[1]	$ 22,311		$ 17,215
Well-Capitalized Ratio, Tier 1 capital	[1],[2]	8.00%		8.00%
Actual Ratio, Tier 1 Capital	[1]	15.59%		13.51%
Common equity Tier 1 ratio:
Capital Amount, Common Equity Tier 1	[1]	$ 20,004		$ 17,215
Well Capitalized Ratio Common equity Tier 1	[1],[2]	6.50%		6.50%
Actual Ratio Common equity Tier 1	[1]	13.98%		13.51%
Tier 1 leverage ratio:
Capital Amount, Tier 1 leverage capital		$ 22,311		$ 17,215
Well-Capitalized Ratio, Tier 1 leverage capital	[2]	5.00%		5.00%
Actual Ratio, Tier 1 leverage capital		11.60%		10.06%
Risk weighted assets:
Risk Weighted Assets	[1]	$ 143,072		$ 127,456

[1] Risk weighted assets are calculated under the Basel III Standardized Approach which came into effect on January 1, 2015, replacing the Basel I risk-based approach used in 2014.

[2] 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. The regulatory ratios for an institution to be well-capitalized under Basel III became effective beginning January 1, 2015 and the new ratios are shown for both periods.

[3] 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 in both periods are the required regulatory minimum ratios beginning in 2015.