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Investment in Securities - Additional Information (Detail) (JPY ¥)
In Millions, unless otherwise specified
 12 Months Ended
Mar. 31, 2014
Investment
Mar. 31, 2013
Investment
Mar. 31, 2012
Schedule of Investments [Line Items]      
Net unrealized holding gains (losses) on trading securities ¥ 3,083 ¥ 1,662 ¥ 4,730
Proceeds from sales of available-for-sale securities 318,697 417,534 279,367
Available-for-sale securities gross realized gains 14,517 17,830 9,882
Available-for-sale securities gross realized losses 368 578 963
Write-downs of securities 7,989 22,838 16,470
Aggregate carrying amount of other securities accounted for under the cost method 80,953 86,406  
Aggregate carrying amount of other securities not evaluated for impairment 72,089 83,591  
Investment funds fair value 11,433 5,800  
Number of investment securities in an unrealized loss position 184 132  
Interest income on investment securities 12,393 11,505 15,169
Carrying amount of debt securities acquired with evidence of deterioration of credit quality 1,267 5,556  
Nominal value of debt securities acquired with evidence of deterioration of credit quality 6,112 14,951  
Outstanding balance of accretable yield of debt securities acquired with evidence of deterioration of credit quality 1,074 4,994  
CMBS and RMBS in the U.S., and other asset-backed securities
      
Schedule of Investments [Line Items]      
Non-credit components of other-than-temporary impairments, gross unrealized losses 102 435 857
Non-credit components of other-than-temporary impairments, gross unrealized gains 59    
Non-credit components of other-than-temporary impairments losses, accumulated other comprehensive income 65 277 547
Non-credit components of other-than-temporary impairments gains, accumulated other comprehensive income 38    
Other securities
      
Schedule of Investments [Line Items]      
Investment funds fair value 6,317 5,800  
Available-for-sale securities
      
Schedule of Investments [Line Items]      
Investment funds fair value ¥ 5,116