Retained Earnings and Regulatory Capital Requirements - Capital Amounts and Ratios in Accordance With Current Banking Regulations (Details) (USD $) In Millions, unless otherwise specified	Mar. 31, 2015		Dec. 31, 2014
HSBC USA Inc [Member]
Total capital ratio:
Capital Amount	$ 24,732		$ 21,017
Well-Capitalized Ratio	10.00%	[1],[2]	10.00%	[3]
Actual Ratio, Total Capital	16.34%		15.78%	[3]
Tier 1 capital ratio:
Capital Amount, Tier 1 capital	19,089		15,205
Well-Capitalized Ratio, Tier 1 capital	6.00%	[1],[2]	6.00%	[1]
Actual Ratio, Tier 1 Capital	12.61%		11.41%	[3]
Common equity Tier 1 ratio:
Capital Amount, Common Equity Tier 1	17,830		13,754
Well Capitalized Ratio Common equity Tier 1	4.50%	[1],[2]	4.50%	[1]
Actual Ratio Common equity Tier 1	11.78%		10.33%	[3]
Tier 1 leverage ratio:
Capital Amount, Tier 1 leverage capital	19,089		15,205
Well-Capitalized Ratio, Tier 1 leverage capital	4.00%	[1],[2]	4.00%	[1]
Actual Ratio, Tier 1 leverage capital	9.91%		8.54%	[3]
Risk weighted assets:
Risk Weighted Assets	151,347		133,211
HSBC Bank USA, National Association [Member]
Total capital ratio:
Capital Amount	26,916		22,760
Well-Capitalized Ratio	10.00%	[1],[2]	10.00%	[1]
Actual Ratio, Total Capital	18.55%		17.86%	[3]
Tier 1 capital ratio:
Capital Amount, Tier 1 capital	22,246		17,215
Well-Capitalized Ratio, Tier 1 capital	8.00%	[1],[2]	8.00%	[1]
Actual Ratio, Tier 1 Capital	15.33%		13.51%	[3]
Common equity Tier 1 ratio:
Capital Amount, Common Equity Tier 1	19,863		17,215
Well Capitalized Ratio Common equity Tier 1	6.50%	[1],[2]	6.50%	[1]
Actual Ratio Common equity Tier 1	13.69%		13.51%	[3]
Tier 1 leverage ratio:
Capital Amount, Tier 1 leverage capital	22,246		17,215
Well-Capitalized Ratio, Tier 1 leverage capital	5.00%	[1],[2]	5.00%	[1]
Actual Ratio, Tier 1 leverage capital	12.02%		10.06%	[3]
Risk weighted assets:
Risk Weighted Assets	$ 145,121		$ 127,456

[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. 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.

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

[3] At March 31, 2015, risk weighted assets are calculated under the Basel III Standardized Approach, which replaced the Basel I risk-based guidance for determining risk weighted assets beginning January 1, 2015.