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 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 | 
                                                955
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                82
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                1,010
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                82
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                1,092
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                1,037
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                935
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                987
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                993
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                946
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                939
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                987
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                997
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                952
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
| Average number of temporary employees | — | — | — | — | 
                                                
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                95
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                95
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                94
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                94
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                95
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                96
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                101
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                100
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
| Average age (Years) | — | — | — | — | — | 
                                                45.3
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | — | — | — | — | — | — | — | — | 
| Average length of service (Years) | — | — | — | — | — | 
                                                18.4
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | — | — | — | — | — | — | — | — | 
| Average annual salary | — | — | — | — | — | 
                                                10,896,505
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | — | — | — | — | — | — |