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4. CONCESSIONS AND AUTHORIZATIONS (Details 2) R$ in Millions | 12 Months Ended
--- | ---
Dec. 31, 2020 BRL (R$)
Irape Enterprise [member] |
Disclosure Of Present Value And Nominal Value Portion To Be Paid [line items] |
Percentage interest | 100.00%
Amounts paid in 2019 | R$ 2
Nominal value of amounts to be paid in the next 12 months | R$ 2
Queimadao Consortium Enterprise [member] |
Disclosure Of Present Value And Nominal Value Portion To Be Paid [line items] |
Percentage interest | 82.50%
Amounts paid in 2019 | R$ 1
Nominal value of amounts to be paid in the next 12 months | R$ 1

X
- Definition Concession amount paid. + References No definition available. + Details
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Namespace Prefix: | cig_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration

X
- Definition Disclosure of present value and nominal value portion to be paid line items. + References No definition available. + Details
Name: | cig_DisclosureOfPresentValueAndNominalValuePortionToBePaidLineItems
Namespace Prefix: | cig_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration

X
- Definition Nominal value of amounts to be paid in next twelve months. + References No definition available. + Details
Name: | cig_NominalValueOfAmountsToBePaidInNextTwelveMonths
Namespace Prefix: | cig_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | instant

X
- Definition Percentage of concession interest. + References No definition available. + Details
Name: | cig_PercentageOfConcessionInterest
Namespace Prefix: | cig_
Data Type: | num:percentItemType
Balance Type: | na
Period Type: | duration

X
- Details
Name: | ifrs-full_ClassesOfPropertyPlantAndEquipmentAxis=cig_IrapeEnterpriseMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | ifrs-full_ClassesOfPropertyPlantAndEquipmentAxis=cig_QueimadaoConsortiumEnterpriseMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |