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The Annual Tariff Adjustment- Additional Information (Detail) - Cemig Distribution [member]
May 28, 2018
Disclosure Of Financial Assets And Financial Liabilities With The Tariff Adjustments [line items]  
Percentage of annual tariffs adjustment 23.19%
Percentage of annual tariff adjustment manageable cost 4.30%
Percentage of annual tariffs remaining after adjustment 18.89%
Non-manageable (Portion A) costs [member]  
Disclosure Of Financial Assets And Financial Liabilities With The Tariff Adjustments [line items]  
Percentage of annual tariffs adjustment 9.00%
Other financial components [member]  
Disclosure Of Financial Assets And Financial Liabilities With The Tariff Adjustments [line items]  
Percentage of annual tariffs adjustment 9.89%