Available-for-Sale Securities Measured at Fair Value (Parenthetical) (Detail) (Maximum)	Mar. 31, 2012
Asset-backed securities and collateralized mortgage obligations
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale securities, maturities	26 years
Corporate notes and bonds
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale securities, maturities	3 years