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Principal assumptions on provisions valuation (Details)
 12 Months Ended
Dec. 31, 2017
Dec. 31, 2016
PCBs [Member]    
Disclosure of Principal assumptions on provisions valuation [Line Items]    
Inflation rate 1.23% 1.29%
Discount rate 2.55% 2.77%
Nuclear plants [Member]    
Disclosure of Principal assumptions on provisions valuation [Line Items]    
Inflation rate 1.21% 1.40%
Discount rate 2.94% 3.55%
Spent fuel [Member]    
Disclosure of Principal assumptions on provisions valuation [Line Items]    
Inflation rate 2.93% 2.93%
Discount rate 4.49% 4.49%