Regulatory Capital - Additional Information (Detail) (USD $) In Millions, unless otherwise specified	9 Months Ended
	Sep. 30, 2012	Dec. 31, 2011
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items]
Deferred tax assets excluded in the computation of regulatory capital	$ 999	$ 363
HSBC Bank USA [Member]
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items]
Contributions to subsidiary in part to provide capital support for receivables purchased from our affiliates	2
Capital requirements, risk-based capital charge	100.00%
Net book value of low quality credit card receivables sold by subsidiary		$ 266