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Investment in Securities (Summary of Contractual Maturities of Available-for-Sale Debt Securities and Held-to-Maturity Debt Securities) (Detail) - JPY (¥)
¥ in Millions
Mar. 31, 2023
Mar. 31, 2022
Available-for-sale debt securities, amortized cost    
Due within one year ¥ 75,103  
Due after one to five years 305,405  
Due after five to ten years 378,144  
Due after ten years 1,730,206  
Available-for-sale debt securities, Amortized cost 2,488,858 ¥ 2,276,425
Available-for-sale debt securities, fair value    
Due within one year 75,662  
Due after one to five years 305,832  
Due after five to ten years 364,070  
Due after ten years 1,489,044  
Available-for-sale debt securities 2,234,608 2,174,891
Held-to-maturity debt securities, amortized cost    
Due after five to ten years 28,658  
Due after ten years 86,101  
Held-to-maturity securities, Amortized cost 114,759 ¥ 114,312
Held-to-maturity debt securities, fair value    
Due after five to ten years 32,204  
Due after ten years 97,474  
Held-to-maturity securities, fair value ¥ 129,678