9. INVESTMENTS (Details 5)	12 Months Ended
Dec. 31, 2018
Gross Margin
Disclosure of fair value measurement of assets [line items]
Main assumptions (Until 2057)	Based on market studies to capture operations costs and loads, according studied of market trends.
Estimated Costs
Disclosure of fair value measurement of assets [line items]
Main assumptions (Until 2057)	Costs based on studies and market trends.
Growth rate in perpetuity
Disclosure of fair value measurement of assets [line items]
Main assumptions (Until 2057)	Growth rate was not considered due to the projection model until the end of the concession.
Discount rate
Disclosure of fair value measurement of assets [line items]
Main assumptions (Until 2057)	Between 5.1% to 7.9% in real terms.

Based on market studies to capture operations costs and loads, according studied of market trends.

Growth rate was not considered due to the projection model until the end of the concession.