| 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 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 | 
                                                4,592
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                995
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                3,134
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                3,805
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                12,526
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                3,570
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                3,570
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                3,598
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                12,776
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                12,885
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                3,674
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                3,703
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                12,949
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                13,050
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                3,668
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
| Average age (Years) | — | — | — | — | — | — | — | — | 
                                                42.2
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | — | — | — | — | — | — | — | — | — | 
| Average length of service (Years) | — | — | — | — | — | — | — | — | 
                                                20.4
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | — | — | — | — | — | — | — | — | — | 
| Average annual salary | — | — | — | — | — | — | — | — | 
                                                8,427,313
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | — | — | — | — | — | — | — |