Other short-term borrowings (Parenthetical) (Detail)	Mar. 31, 2012	Mar. 31, 2011
Short-term Debt [Line Items]
Federal Home Loan Bank Advances General Debt Obligations Disclosures Interest Rate Range From	0.37%	0.36%
Federal Home Loan Bank Advances General Debt Obligations Disclosures Interest Rate Range To	0.40%	0.40%
Term Funds Interest Rate Range From	0.00%	0.70%
Term Funds Interest Rate Range To	0.00%	1.05%