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12. ESCROW DEPOSITS (Details Narrative) - BRL (R$) R$ in Millions | Dec. 31, 2020 | Feb. 13, 2020
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Disclosure of escrow deposits [line items] |  |
Escrow deposits | R$ 6 |
Cemig D and Cemig GT [member] |  |
Disclosure of escrow deposits [line items] |  |
Escrow deposits |  | R$ 1,382
Ceming GT [member] |  |
Disclosure of escrow deposits [line items] |  |
Escrow deposits |  | 1,186
Cemig D [member] |  |
Disclosure of escrow deposits [line items] |  |
Escrow deposits |  | R$ 196

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- Definition Amount in escrow deposits + References No definition available. + Details
Name: | cig_AmountInEscrowDeposits
Namespace Prefix: | cig_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

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- Definition Line items represents information about escrow deposits. + References No definition available. + Details
Name: | cig_DisclosureOfEscrowDepositsLineItems
Namespace Prefix: | cig_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration

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- Details
Name: | ifrs-full_CategoriesOfRelatedPartiesAxis=cig_CemigDAndCemigGTMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

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- Details
Name: | ifrs-full_CategoriesOfRelatedPartiesAxis=cig_CemingGTMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

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- Details
Name: | ifrs-full_CategoriesOfRelatedPartiesAxis=cig_CemigDMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |