v3.26.1
Business combinations - Additional Information (Detail) - JPY (¥)
¥ in Millions
12 Months Ended
Dec. 01, 2025
Apr. 01, 2024
Mar. 31, 2026
Mar. 31, 2025
Business Combination [Line Items]        
Business Combination Separately Recognized Transaction Acquisition Related Cost Expensed Statement of Income or Comprehensive Income Extensible Enumeration Not Disclosed Flag     true  
Macquarie Management Holdings Inc [Member]        
Business Combination [Line Items]        
Percentage of equity interests acquired 100.00%      
Purchase price ¥ 288,800      
Overall acquisition-related costs     ¥ 7,034  
Acquisition-related costs     5,120 ¥ 1,914
Increase in assets under management 39,891      
Net income contributed after the acquisition date ¥ 6,409      
Business acquisitions pro forma acquisition related costs   ¥ 7,099    
Business acquisitions pro forma amortization of intangible assets     ¥ 10,025 ¥ 10,153
Macquarie Management Holdings Inc [Member] | Employee Severance [Member]        
Business Combination [Line Items]        
Business acquisitions pro forma employment related expenses   ¥ 10,739