Key Financial Data Of Group
| Concept | As at 2023-12-31 | 2023-10-01 to 2023-12-31 | 2023-04-01 to 2023-12-31 | As at 2023-03-31 | 2022-04-01 to 2023-03-31 | As at 2022-12-31 | 2022-04-01 to 2022-12-31 | 2022-10-01 to 2022-12-31 | 
|---|---|---|---|---|---|---|---|---|
| Key financial data of group | ||||||||
| Business results of group | ||||||||
| Ordinary profit (loss) | — | — | 
                                                740,000,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | 
                                                1,074,000,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | 
                                                655,000,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | 
| Net assets | 
                                                11,233,000,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | 
                                                10,951,000,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | 
                                                10,672,000,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | 
| Total assets | 
                                                19,125,000,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | 
                                                18,354,000,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | 
                                                16,347,000,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | 
| Basic earnings (loss) per share | — | 
                                                28.12
                                                
                                             | 
                                                40.60
                                                
                                             | — | 
                                                59.10
                                                
                                             | — | 
                                                35.53
                                                
                                             | 
                                                14.60
                                                
                                             | 
| Diluted earnings per share | — | — |  | — |  | — |  | — | 
| Equity-to-asset ratio | 
                                                0.587
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | — | — | 
                                                0.597
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | — | 
                                                0.653
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | — | — |