Employees
| Concept | As at 2024-03-31 | As at 2024-03-31 | 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 | As at 2020-03-31 | As at 2020-03-31 | 
|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Employees | ||||||||||||
| Information about reporting company | ||||||||||||
| Information about employees of reporting company | ||||||||||||
| Number of employees | 
                                                3,233
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                1,721
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                3,496
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                263
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                3,941
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                1,624
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                1,603
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                4,018
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                4,174
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                1,591
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                1,591
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                4,662
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
| Average number of temporary employees | 
                                                868
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                773
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                912
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                44
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                732
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                575
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                520
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                703
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                680
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                436
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                443
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                732
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
| Average age (Years) | — | 
                                                42.2
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | — | — | — | — | — | — | — | — | — | — | 
| Average length of service (Years) | — | 
                                                13.3
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | — | — | — | — | — | — | — | — | — | — | 
| Average annual salary | — | 
                                                10,003,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | — | — | — | — | — | — | — | — |