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Other information about investments (Details)
 12 Months Ended
Dec. 31, 2018
EUR (€)
Dec. 31, 2017
EUR (€)
Disclosure of subsidiaries [line items]    
Share capital € 4,005,000,000 € 4,005,000,000
Parent [Member]    
Disclosure of subsidiaries [line items]    
Share capital € 4,005,358,876  
Parent [Member] | Cassa Depositi ePrestiti SpA [Member]    
Disclosure of subsidiaries [line items]    
Name of parent entity [1] Eni SpA(#)  
Registered office Rome  
Principal place of business Italy  
Name of Shareholders Cassa Depositi e Prestiti SpA  
Equity Method Investments, Ownership Percentage 25.76  
Parent [Member] | Ministero dell Economia e delle Finanze [Member]    
Disclosure of subsidiaries [line items]    
Name of Shareholders Ministero dell’Economia e delle Finanze  
Equity Method Investments, Ownership Percentage 4.34  
Parent [Member] | ENI SPA [Member]    
Disclosure of subsidiaries [line items]    
Name of Shareholders Eni SpA  
Equity Method Investments, Ownership Percentage 0.91  
Parent [Member] | Other Shareholders [Member]    
Disclosure of subsidiaries [line items]    
Name of Shareholders Other shareholders  
Equity Method Investments, Ownership Percentage 68.99  
[1] Company with shares quoted in the regulated market of Italy or of other EU countries