CONSOLIDATED BALANCE SHEET (Parenthetical) (USD $)	Dec. 31, 2012	Dec. 31, 2011
Securities held-to-maturity, fair value	$ 1,800,000,000	$ 2,300,000,000
Loans held for sale, fair value	465,000,000	377,000,000
Interest bearing, designated under fair value option	8,700,000,000	9,800,000,000
Long-term debt, designated under fair value option	7,280,000,000	5,000,000,000
Common stock, par value	$ 5	$ 5
Common stock, shares authorized	150,000,000	150,000,000
Common stock, shares issued	713	712
Common stock, shares outstanding	713	712
HSBC Bank USA, National Association [Member]
Securities held-to-maturity, fair value	1,800,000,000	2,300,000,000
Loans held for sale, fair value	465,000,000	377,000,000
Interest bearing, designated under fair value option	8,700,000,000	9,800,000,000
Long-term debt, designated under fair value option	$ 2,600,000,000	$ 2,200,000,000
Common stock, par value	$ 100	$ 100
Common stock, shares authorized	50,000	50,000
Common stock, shares issued	20,016	20,015
Common stock, shares outstanding	20,016	20,015