v3.26.1
Financial risk management - Summary of Gross Carrying Amount For Loans At Amortized Cost Based On Credit Ratings (Detail) - JPY (¥)
¥ in Millions
Mar. 31, 2026
Mar. 31, 2025
Disclosure of credit risk exposure [line items]    
Exposure to credit risk of loans ¥ 3,020,544 ¥ 22,435,594
Banking Business in Financial Services Segment Normal [Member]    
Disclosure of credit risk exposure [line items]    
Exposure to credit risk of loans   3,779,876
Banking Business in Financial Services Segment Normal [Member] | 12-month expected credit losses [member]    
Disclosure of credit risk exposure [line items]    
Exposure to credit risk of loans   3,779,029
Banking Business in Financial Services Segment Normal [Member] | Lifetime expected credit losses [member]    
Disclosure of credit risk exposure [line items]    
Exposure to credit risk of loans   847
Banking Business In Financial Services Segment Other Than Normal [Member]    
Disclosure of credit risk exposure [line items]    
Exposure to credit risk of loans   5,145
Banking Business In Financial Services Segment Other Than Normal [Member] | 12-month expected credit losses [member]    
Disclosure of credit risk exposure [line items]    
Exposure to credit risk of loans   2,400
Banking Business In Financial Services Segment Other Than Normal [Member] | Lifetime expected credit losses [member]    
Disclosure of credit risk exposure [line items]    
Exposure to credit risk of loans   2,745
Housing Loan [Member]    
Disclosure of credit risk exposure [line items]    
Exposure to credit risk of loans   3,763,747
Housing Loan [Member] | Banking Business in Financial Services Segment Normal [Member]    
Disclosure of credit risk exposure [line items]    
Exposure to credit risk of loans   3,758,693
Housing Loan [Member] | Banking Business in Financial Services Segment Normal [Member] | 12-month expected credit losses [member]    
Disclosure of credit risk exposure [line items]    
Exposure to credit risk of loans   3,758,168
Housing Loan [Member] | Banking Business in Financial Services Segment Normal [Member] | Lifetime expected credit losses [member]    
Disclosure of credit risk exposure [line items]    
Exposure to credit risk of loans   525
Housing Loan [Member] | Banking Business In Financial Services Segment Other Than Normal [Member]    
Disclosure of credit risk exposure [line items]    
Exposure to credit risk of loans   5,054
Housing Loan [Member] | Banking Business In Financial Services Segment Other Than Normal [Member] | 12-month expected credit losses [member]    
Disclosure of credit risk exposure [line items]    
Exposure to credit risk of loans   2,393
Housing Loan [Member] | Banking Business In Financial Services Segment Other Than Normal [Member] | Lifetime expected credit losses [member]    
Disclosure of credit risk exposure [line items]    
Exposure to credit risk of loans   2,661
Other Loan [Member]    
Disclosure of credit risk exposure [line items]    
Exposure to credit risk of loans   21,274
Other Loan [Member] | Banking Business in Financial Services Segment Normal [Member]    
Disclosure of credit risk exposure [line items]    
Exposure to credit risk of loans   21,183
Other Loan [Member] | Banking Business in Financial Services Segment Normal [Member] | 12-month expected credit losses [member]    
Disclosure of credit risk exposure [line items]    
Exposure to credit risk of loans   20,861
Other Loan [Member] | Banking Business in Financial Services Segment Normal [Member] | Lifetime expected credit losses [member]    
Disclosure of credit risk exposure [line items]    
Exposure to credit risk of loans   322
Other Loan [Member] | Banking Business In Financial Services Segment Other Than Normal [Member]    
Disclosure of credit risk exposure [line items]    
Exposure to credit risk of loans   91
Other Loan [Member] | Banking Business In Financial Services Segment Other Than Normal [Member] | 12-month expected credit losses [member]    
Disclosure of credit risk exposure [line items]    
Exposure to credit risk of loans   7
Other Loan [Member] | Banking Business In Financial Services Segment Other Than Normal [Member] | Lifetime expected credit losses [member]    
Disclosure of credit risk exposure [line items]    
Exposure to credit risk of loans   84
Total Loans [Member]    
Disclosure of credit risk exposure [line items]    
Exposure to credit risk of loans   ¥ 3,785,021