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 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 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 | 
                                                1,800
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                5
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                263
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                2,653
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                12
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                1,524
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                2,102
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                208
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                365
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                169
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                141
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                5
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                263
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                2,659
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                2,100
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                2,073
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                2,627
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                2,607
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                2,096
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                2,548
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                2,048
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
| Average number of temporary employees | 
                                                46
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | — | — | 
                                                380
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                2
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | — | — | 
                                                33
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                298
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | — | — | — | 
                                                1
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                372
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | — | — | 
                                                357
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                493
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | — | 
                                                338
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | — | 
| Average age (Years) | — | — | — | — | — | — | — | 
                                                43.0
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | — | — | — | — | — | — | — | — | — | — | — | — | — | — | 
| Average length of service (Years) | — | — | — | — | — | — | — | 
                                                18.2
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | — | — | — | — | — | — | — | — | — | — | — | — | — | — | 
| Average annual salary | — | — | — | — | — | — | — | 
                                                10,783,866
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | — | — | — | — | — | — | — | — | — | — | — | — |