Commitments, contingencies and guarantees - Information on Derivative Contracts and Standby Letters of Credit and Other Guarantees (Parenthetical) (Detail) (JPY ¥) In Millions, unless otherwise specified	Mar. 31, 2013	Mar. 31, 2012
Contingencies And Commitments [Line Items]
Collateral held in connection with standby letters of credit and other guarantees	¥ 6,374	¥ 6,377