v3.26.1
Income taxes - Additional Information (Detail) - JPY (¥)
¥ in Millions
 12 Months Ended
Mar. 31, 2027
Mar. 31, 2026
Mar. 31, 2025
Mar. 31, 2024
Statements [Line Items]        
Tax expense (income)   ¥ 367,108 ¥ 257,480 ¥ 239,105
Increase decrease in tax expenses from repayment of capital from a subsidiary     48,373  
Increase decrease in tax expenses from dissolution of a subsidiary     ¥ 35,278  
Statutory tax rate   31.50% 31.50% 31.50%
Temporary differences associated with investments in subsidiaries, branches and associates and interests in joint arrangements for which deferred tax liabilities have not been recognised   ¥ 1,221,573 ¥ 1,117,684  
Undistributed earnings   5,294,890 6,678,168  
Deferred tax expense (income) recognised in profit or loss   61,544    
Remeasurement gain for the pre-owned equity interest   116,939    
Deferred tax assets   560,800 559,284  
Deferred tax liabilities   211,391 175,228  
Country of domicile [member]        
Statements [Line Items]        
Tax expense (income)   171,666 64,219 ¥ 120,758
Foreign countries [member]        
Statements [Line Items]        
Tax expense (income)   ¥ 195,442 193,261 ¥ 118,347
Unused tax credits [member]        
Statements [Line Items]        
Description of expiry date of deductible temporary differences, unused tax losses and unused tax credits   As of March 31, 2025 and 2026, the expected expiration period of the tax credit carryforwards for which no deferred tax asset is recognized was mostly within 5 years.    
Undistributed Earnings Of Foreign Subsidiaries And Corporate Joint Ventures [Member]        
Statements [Line Items]        
Undistributed earnings   ¥ 19,545 17,883  
Unrealised foreign exchange gains (losses) [member]        
Statements [Line Items]        
Deferred tax assets   197,149 173,711  
Deferred tax liabilities   ¥ 1,499,571 ¥ 1,047,225  
Change of applicable tax rate [member]        
Statements [Line Items]        
Statutory tax rate 32.30%