| 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 | 
                                                5,591
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                264
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                3
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                5,858
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                2,365
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                2,230
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                5,606
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                2,166
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                5,885
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                2,131
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                6,018
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                5,890
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                2,116
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
| Average age (Years) | — | — | — | — | 
                                                41.6
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | — | — | — | — | — | — | — | — | 
| Average length of service (Years) | — | — | — | — | 
                                                15.0
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | — | — | — | — | — | — | — | — | 
| Average annual salary | — | — | — | — | 
                                                11,291,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | — | — | — | — | — | — |