Employees
| Concept | 
                                    
                                        As at 2025-03-31  | 
                            
                                
                                    
                                        As at 2025-03-31  | 
                            
                        
|---|---|---|
| Employees | ||
| Metrics related to human capital diversity | ||
| Metrics of consolidated subsidiaries | ||
| Consolidated subsidiaries | 
                                        
                                             
                                                エム・ピー・エム・オペレーション㈱
                                                
                                             
                                        
                                     | 
                                
                                    
                                        
                                             
                                                三菱製紙㈱
                                                
                                             
                                        
                                     | 
                                
                            
| Ratio of male employees taking childcare leave | ||
| All employees | 
                                        
                                             
                                                0.000
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             
                                        
                                     | 
                                
                                    
                                        
                                             
                                                0.333
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             
                                        
                                     | 
                                
                            
| Differences in wages between male and female employees | ||
| All employees | 
                                        
                                             
                                                0.687
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             
                                        
                                     | 
                                
                                    
                                        
                                             
                                                0.581
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             
                                        
                                     | 
                                
                            
| Regular employees | 
                                        
                                             
                                                0.727
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             
                                        
                                     | 
                                
                                    
                                        
                                             
                                                0.694
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             
                                        
                                     | 
                                
                            
| Non-regular employees | 
                                        
                                             
                                                0.782
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             
                                        
                                     | 
                                
                                    
                                        
                                             
                                                0.555
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             
                                        
                                     |