Employees
| Concept | As at 2025-03-31 | 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 2023-03-31 | As at 2023-03-31 | As at 2022-03-31 | As at 2022-03-31 | As at 2021-03-31 | As at 2021-03-31 | 
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Employees | |||||||||||||
| Information about reporting company | |||||||||||||
| Information about employees of reporting company | |||||||||||||
| Number of employees | 
                                                815
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                58
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                102
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                975
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                815
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                810
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                966
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                966
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                805
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                801
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                961
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                944
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                793
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
| Average age (Years) | — | — | — | — | 
                                                45.4
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | — | — | — | — | — | — | — | — | 
| Average length of service (Years) | — | — | — | — | 
                                                18.5
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | — | — | — | — | — | — | — | — | 
| Average annual salary | — | — | — | — | 
                                                9,629,666
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | — | — | — | — | — | — |