v3.26.1
Fair Value Measurements - Changes in Level 3 Assets and Liabilities Measured at Fair Value on Recurring Basis (Detail) - Fair value, measurements, recurring [Member] - JPY (¥)
¥ in Millions
 12 Months Ended
Mar. 31, 2026
Mar. 31, 2025
Disclosure details of fair value measurements of financial assets [Line items]    
Balance at beginning of year ¥ 293,257 ¥ 432,259
Net income (loss) 33,386 (62,873)
Other comprehensive income (loss) 17,978 (40,717)
Purchases and issuances 866,955 45,902
Sales and settlements (12,200) (10,245)
Transfer to (from) Level 3 (1,452) (81,009)
Others 33,749 9,939
Balance at end of year 1,231,673 293,257
Unrealized gains or losses included in profit or loss on assets held at March 31 33,376 (87,741)
Total 33,376 (87,741)
Public and corporate bonds [Member]    
Disclosure details of fair value measurements of financial assets [Line items]    
Balance at beginning of year 30,111 31,170
Net income (loss) 35 (8)
Purchases and issuances 9,692 9,572
Sales and settlements (7,399) (9,210)
Transfer to (from) Level 3 (1,452) (3,125)
Others 659 1,711
Balance at end of year 31,646 30,111
Unrealized gains or losses included in profit or loss on assets held at March 31 25 (76)
Total 25 (76)
Stocks [Member]    
Disclosure details of fair value measurements of financial assets [Line items]    
Balance at beginning of year 238,346 401,089
Net income (loss) 8,074 (87,665)
Other comprehensive income (loss) 17,978 (40,717)
Purchases and issuances 857,263 36,330
Sales and settlements (4,801) (1,035)
Transfer to (from) Level 3   (77,884)
Others 31,371 8,228
Balance at end of year 1,148,232 238,346
Unrealized gains or losses included in profit or loss on assets held at March 31 8,074 (87,665)
Total 8,074 (87,665)
Derivative financial instruments [Member]    
Disclosure details of fair value measurements of financial assets [Line items]    
Balance at beginning of year 24,800  
Net income (loss) 25,277 24,800
Others 1,718  
Balance at end of year 51,795 ¥ 24,800
Unrealized gains or losses included in profit or loss on assets held at March 31 25,277  
Total ¥ 25,277