Shareholdings
| Concept | 
                                    
                                        As at 2025-03-31  | 
                            
                                
                                    
                                        2024-04-01 to 2025-03-31  | 
                            
                        
|---|---|---|
| Shareholdings | ||
| Reporting company | ||
| Investment shares held for purposes other than pure investment | ||
| Shares not listed | ||
| Number of issues | 
                                        
                                             
                                                20
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             
                                        
                                     | 
                                
                                    — | 
| Carrying amount | 
                                        
                                             
                                                224,000,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             
                                        
                                     | 
                                
                                    — | 
| Number of issues whose number of shares increased | — | 
                                        
                                             
                                                
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             
                                        
                                     | 
                                
                            
| Total acquisition cost for increased shares | — | 
                                        
                                             
                                                
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             
                                        
                                     | 
                                
                            
| Reason for increase in number of shares | — | 
                                        
                                             | 
                                
                            
| Number of issues whose number of shares decreased | — | 
                                        
                                             
                                                
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             
                                        
                                     | 
                                
                            
| Total sale amount for decreased shares | — | 
                                        
                                             
                                                
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             
                                        
                                     | 
                                
                            
| Shares other than those not listed | ||
| Number of issues | 
                                        
                                             
                                                1
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             
                                        
                                     | 
                                
                                    — | 
| Carrying amount | 
                                        
                                             
                                                307,000,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             
                                        
                                     | 
                                
                                    — | 
| Number of issues whose number of shares increased | — | 
                                        
                                             
                                                1
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             
                                        
                                     | 
                                
                            
| Total acquisition cost for increased shares | — | 
                                        
                                             
                                                300,000,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             
                                        
                                     | 
                                
                            
| Reason for increase in number of shares | — | 
                                        
                                             
                                                工事請負に係る中長期的な受注、主に住宅や事務所ビル等の建築工事における受注の確保に向けて、株式取得先との友好的な関係の維持、強化を図るため、保有しております。
                                                
                                             
                                        
                                     | 
                                
                            
| Number of issues whose number of shares decreased | — | 
                                        
                                             
                                                2
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             
                                        
                                     | 
                                
                            
| Total sale amount for decreased shares | — | 
                                        
                                             
                                                1,884,000,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             
                                        
                                     |