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30. RELATED PARTY TRANSACTIONS (Details 1) - BRL (R$) R$ in Millions | Dec. 31, 2020 | Dec. 31, 2019
--- | --- | ---
Disclosure of transactions between related parties [line items] |  |
Dividends receivable | R$ 188 | R$ 186
Light [member] |  |
Disclosure of transactions between related parties [line items] |  |
Dividends receivable | 71 | 73
Alianca geracao [member] |  |
Disclosure of transactions between related parties [line items] |  |
Dividends receivable | 114 | 103
Others [member] |  |
Disclosure of transactions between related parties [line items] |  |
Dividends receivable | R$ 3 | R$ 10

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- Definition Dividends Receivable from subsidiaries. + References No definition available. + Details
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Namespace Prefix: | cig_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

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- Definition Line items represent concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes of the table. + References No definition available. + Details
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Namespace Prefix: | ifrs-full_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration

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- Details
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Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

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- Details
Name: | ifrs-full_SignificantInvestmentsInSubsidiariesAxis=cig_AliancaGeracaoMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

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- Details
Name: | ifrs-full_SignificantInvestmentsInSubsidiariesAxis=cig_OthersMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |