Consolidated Balance Sheet (Parenthetical) (USD $)	Dec. 31, 2011	Dec. 31, 2010
Securities held to maturity, fair value	$ 2,300,000,000	$ 3,400,000,000
Loans held for sale, designated under fair value option	377,000,000	1,300,000,000
Interest bearing, designated under fair value option	9,800,000,000	7,400,000,000
Long-term debt, designated under fair value option	5,000,000,000	5,400,000,000
Common stock, par value	$ 5	$ 5
Common stock, shares authorized	150,000,000	150,000,000
Common stock, shares outstanding	712	712
Common stock, shares issued	712	712
HSBC BANK USA, National Association
Securities held to maturity, fair value	2,300,000,000	3,400,000,000
Loans held for sale, designated under fair value option	377,000,000	1,300,000,000
Interest bearing, designated under fair value option	9,800,000,000	7,400,000,000
Long-term debt, designated under fair value option	$ 2,200,000,000	$ 2,500,000,000
Common stock, par value	$ 100	$ 100
Common stock, shares authorized	50,000	50,000
Common stock, shares outstanding	20,015	20,013
Common stock, shares issued	20,015	20,013