Regulatory Capital (Details) (USD $)	6 Months Ended
	Jun. 30, 2012	Dec. 31, 2011
Regulatory Capital (Textual) [Abstract]
Consolidated assets under tier one common capital	$ 50,000,000,000
Capital charge for measuring and reporting risk-based capital and related ratios, not part of transferred portfolios	8.00%
Deferred tax assets excluded in the computation of regulatory capital	959,000,000	363,000,000
HSBC USA Inc [Member]
Total capital ratio:
Capital Amount	20,964,000,000	21,908,000,000
Well-Capitalized Minimum Ratio, Total capital	10.00%	10.00%
Actual Ratio, Total Capital	20.61%	18.39%
Tier 1 capital ratio:
Capital Amount, Tier 1 capital	14,588,000,000	15,179,000,000
Well-Capitalized Minimum Ratio, Tier 1 capital	6.00%	6.00%
Actual Ratio, Tier 1 Capital	14.34%	12.74%
Tier 1 common ratio:
Capital Amount, Tier 1 common capital	12,181,000,000	12,773,000,000
Well-Capitalized Minimum Ratio, Tier 1 common capital	5.00%	5.00%
Actual Ratio, Tier 1 common capital	11.97%	10.72%
Tier 1 leverage ratio:
Capital Amount, Tier 1 leverage capital	14,588,000,000	15,179,000,000
Well-Capitalized Minimum Ratio, Tier 1 leverage capital	3.00%	3.00%
Actual Ratio, Tier 1 leverage capital	7.45%	7.43%
Risk weighted assets:
Risk Weighted Assets	101,728,000,000	119,099,000,000
HSBC Bank USA [Member]
Total capital ratio:
Capital Amount	21,579,000,000	22,390,000,000
Well-Capitalized Minimum Ratio, Total capital	10.00%	10.00%
Actual Ratio, Total Capital	21.75%	18.86%
Tier 1 capital ratio:
Capital Amount, Tier 1 capital	15,511,000,000	15,996,000,000
Well-Capitalized Minimum Ratio, Tier 1 capital	6.00%	6.00%
Actual Ratio, Tier 1 Capital	15.64%	13.48%
Tier 1 common ratio:
Capital Amount, Tier 1 common capital	15,511,000,000	15,996,000,000
Well-Capitalized Minimum Ratio, Tier 1 common capital	5.00%	5.00%
Actual Ratio, Tier 1 common capital	15.64%	13.48%
Tier 1 leverage ratio:
Capital Amount, Tier 1 leverage capital	15,511,000,000	15,996,000,000
Well-Capitalized Minimum Ratio, Tier 1 leverage capital	5.00%	5.00%
Actual Ratio, Tier 1 leverage capital	8.04%	7.98%
Risk weighted assets:
Risk Weighted Assets	99,193,000,000	118,688,000,000
Regulatory Capital (Additional Textual) [Abstract]
Contributions to Subsidiary in Part to Provide Capital Support for Receivables Purchased from Our Affiliates	2,000,000
Net book value of low-quality credit card receivables sold		$ 266,000,000
Capital requirements, risk-based capital charge	100.00%