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8. RECEIVABLES FROM CUSTOMERS, TRADERS AND POWER TRANSPORT CONCESSION HOLDERS (Details 2) - BRL (R$) R$ in Millions | 12 Months Ended
--- | ---
Dec. 31, 2020 | Dec. 31, 2019 | Dec. 31, 2018
Cemig GT [member] |  |  |
Disclosure Of Advances From Customers [line items] |  |  |
Beginning balance | R$ 810 | R$ 751 | R$ 568
Effect of adoption of IFRS 9 on Jan. 1, 2018 |  |  | 150
Additions | 146 |  | 264
Write-off |  |  | (231)
Disposals | (244) |  |
Ending Balance | 712 | 810 | 751
Eletrobras [member] |  |  |
Disclosure Of Advances From Customers [line items] |  |  |
Beginning balance | R$ 810 | 751 |
Additions |  | 238 |
Disposals |  | (179) |
Ending Balance |  | R$ 810 | R$ 751

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- Definition Additions to advances payable. + References No definition available. + Details
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Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | duration

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- Definition Disclosure Of Advances From Customers [line items] + References No definition available. + Details
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Namespace Prefix: | cig_
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Balance Type: | na
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- Definition Represent information about the disposals to advance payable. + References No definition available. + Details
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Namespace Prefix: | cig_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | duration

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- Definition The amount of effect of adoption of ifrs. + References No definition available. + Details
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- Definition Represent information about the writeoff advance payable. + References No definition available. + Details
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Data Type: | xbrli:monetaryItemType
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- Definition The amount of current payments received for goods or services to be provided in the future. [Refer: Advances received] + References Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef -Name IAS -Number 1 -IssueDate 2020-01-01 -Paragraph 55 -URI http://eifrs.ifrs.org/eifrs/xifrs-link?type=IAS&num=1&code=ifrs-tx-2020-en-r&anchor=para_55&doctype=Standard -URIDate 2020-01-01 + Details
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Period Type: | instant

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

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