Shareholdings
| Concept | As at 2025-03-31 | As at 2025-03-31 | As at 2025-03-31 | As at 2025-03-31 | As at 2024-03-31 | As at 2024-03-31 | As at 2024-03-31 | As at 2024-03-31 | 
|---|---|---|---|---|---|---|---|---|
| Shareholdings | ||||||||
| Reporting company | ||||||||
| Details of deemed holdings of shares held for purposes other than pure investment | ||||||||
| Issue | 
                                                みずほフィナンシャルグループ(注1)
                                                
                                             | 
                                                信越化学工業株式会社
                                                
                                             | 
                                                株式会社三菱UFJフィナンシャル・グループ(注1)
                                                
                                             | 
                                                株式会社サンエー化研
                                                
                                             | — | — | — | — | 
| Number of shares | 
                                                26,600
                                                
                                                    
                                                        xbrli:shares
                                                    
                                                
                                             | 
                                                100,000
                                                
                                                    
                                                        xbrli:shares
                                                    
                                                
                                             | 
                                                481,060
                                                
                                                    
                                                        xbrli:shares
                                                    
                                                
                                             | 
                                                600,000
                                                
                                                    
                                                        xbrli:shares
                                                    
                                                
                                             | 
                                                600,000
                                                
                                                    
                                                        xbrli:shares
                                                    
                                                
                                             | 
                                                100,000
                                                
                                                    
                                                        xbrli:shares
                                                    
                                                
                                             | 
                                                481,060
                                                
                                                    
                                                        xbrli:shares
                                                    
                                                
                                             | 
                                                26,600
                                                
                                                    
                                                        xbrli:shares
                                                    
                                                
                                             | 
| Carrying amount | 
                                                64,000,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | 
                                                591,000,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | 
                                                582,000,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | 
                                                313,000,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | 
                                                321,000,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | 
                                                658,000,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | 
                                                749,000,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | 
                                                81,000,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | 
| Purpose of shareholding, overview of business alliance, quantitative effects of shareholding and reason for increase in number of shares | 
                                                議決権行使に関する指図権限
                                                
                                             | 
                                                議決権行使に関する指図権限
                                                
                                             | 
                                                議決権行使に関する指図権限
                                                
                                             | 
                                                議決権行使に関する指図権限
                                                
                                             | — | — | — | — | 
| Whether issuer of aforementioned shares holds reporting company's shares | 
                                                有
                                                
                                             | 
                                                無
                                                
                                             | 
                                                有
                                                
                                             | 
                                                有
                                                
                                             | — | — | — | — |