Employees
| Concept | As at 2024-12-31 | As at 2024-12-31 | As at 2024-12-31 | As at 2024-12-31 | As at 2024-12-31 | As at 2024-12-31 | As at 2024-12-31 | As at 2024-12-31 | As at 2024-12-31 | As at 2024-12-31 | As at 2024-12-31 | As at 2024-12-31 | As at 2023-12-31 | As at 2023-12-31 | As at 2022-12-31 | As at 2022-12-31 | As at 2022-03-31 | As at 2022-03-31 | As at 2021-03-31 | As at 2021-03-31 | As at 2020-03-31 | As at 2020-03-31 | 
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Employees | ||||||||||||||||||||||
| Information about reporting company | ||||||||||||||||||||||
| Information about employees of reporting company | ||||||||||||||||||||||
| Number of employees | 
                                                3,785
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                4,410
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                424
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                6,658
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                3
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                1,681
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                5,450
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                1,053
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                1,470
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                7,763
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                25,337
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                1,460
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                25,303
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                4,033
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                25,211
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                3,849
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                24,584
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                3,370
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                24,050
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                3,356
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                23,635
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                3,068
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
| Average age (Years) | — | 
                                                43.2
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | 
| Average length of service (Years) | — | 
                                                13.5
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | 
| Average annual salary | — | 
                                                8,353,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — |