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Other information about investments (Details 13)
 12 Months Ended
Dec. 31, 2017
EUR (€)
Dec. 31, 2017
USD ($)
Dec. 31, 2016
EUR (€)
Disclosure of subsidiaries [line items]      
Share capital € 4,005,000,000   € 4,005,000,000
Outside Italy [Member] | Other significant investments Gas & Power [Member] | Subsidiaries One [Member]      
Disclosure of subsidiaries [line items]      
Company name Angola LNG Supply Services Llc    
Registered office Wilmington (USA)    
Country of operation USA    
Share capital | $   $ 19,278,782  
Method used to account for investments in subsidiaries [1] Co.    
Outside Italy [Member] | Other significant investments Gas & Power [Member] | Subsidiaries One [Member] | Eni USA Gas M. Llc [Member]      
Disclosure of subsidiaries [line items]      
Name of Shareholders Eni USA Gas M. Llc    
% Ownership 13.60%    
Outside Italy [Member] | Other significant investments Gas & Power [Member] | Subsidiaries One [Member] | Third parties [Member]      
Disclosure of subsidiaries [line items]      
Name of Shareholders Third parties    
% Ownership 86.40%    
Outside Italy [Member] | Other significant investments Gas & Power [Member] | Subsidiaries Two [Member]      
Disclosure of subsidiaries [line items]      
Company name Norsea Gas GmbH    
Registered office Emden (Germany)    
Country of operation Germany    
Share capital € 1,533,875.64    
Method used to account for investments in subsidiaries [1] Co.    
Outside Italy [Member] | Other significant investments Gas & Power [Member] | Subsidiaries Two [Member] | Third parties [Member]      
Disclosure of subsidiaries [line items]      
Name of Shareholders Third parties    
% Ownership 86.96%    
Outside Italy [Member] | Other significant investments Gas & Power [Member] | Subsidiaries Two [Member] | Eni International BV [Member]      
Disclosure of subsidiaries [line items]      
Name of Shareholders Eni International BV    
% Ownership 13.04%    
[1] Jointly controlled entity.