Employees
| 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 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 | 
                                                938
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                987
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                987
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                938
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                900
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                934
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                879
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                854
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                797
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                816
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                732
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                719
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
| Average age (Years) | — | — | — | 
                                                41.1
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | — | — | — | — | — | — | — | — | 
| Average length of service (Years) | — | — | — | 
                                                9.0
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | — | — | — | — | — | — | — | — | 
| Average annual salary | — | — | — | 
                                                8,709,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | — | — | — | — | — | — |