Shareholdings
| Concept | 
                                    
                                        As at 2024-03-31  | 
                            
                                
                                    
                                        As at 2024-03-31  | 
                            
                        
|---|---|---|
| Shareholdings | ||
| Largest holding company | ||
| Investment shares reclassified from held for purposes other than pure investment to held for pure investment | ||
| Issue | 
                                        
                                             
                                                東京海上ホールディングス株式会社
                                                
                                             
                                        
                                     | 
                                
                                    
                                        
                                             
                                                大豊建設株式会社
                                                
                                             
                                        
                                     | 
                                
                            
| Number of shares | 
                                        
                                             
                                                469,650
                                                
                                                    
                                                        xbrli:shares
                                                    
                                                
                                             
                                        
                                     | 
                                
                                    
                                        
                                             
                                                33,000
                                                
                                                    
                                                        xbrli:shares
                                                    
                                                
                                             
                                        
                                     | 
                                
                            
| Carrying amount | 
                                        
                                             
                                                2,208,000,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             
                                        
                                     | 
                                
                                    
                                        
                                             
                                                112,000,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             
                                        
                                     |