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5. OPERATING SEGMENTS (Details 1) - BRL (R$) R$ in Millions |  | 12 Months Ended
--- | --- | ---
Jan. 02, 2019 | [1] | Dec. 31, 2020 | Dec. 31, 2019 | Dec. 31, 2018
Disclosure of revenue [line items] |  |  |  |  |  |
Revenue from supply of energy |  | R$ 26,432 | R$ 26,927 |  | R$ 24,872 |
Revenue from Use of Distribution Systems (the TUSD charge) |  | 3,022 |  |  |  |
CVA and Other financial components in tariff adjustment |  | 455 |  |  |  |
Reimbursement of PIS/Pasep and Cofins over ICMS credits to customers- realization |  | 266 |  |  |  |
Transmission operation and maintenance revenue |  | 280 |  |  |  |
Transmission construction revenue |  | 201 |  |  |  |
Interest revenue arising from the financing component in transmission contract asset |  | 438 |  |  |  |
Generation assets - indemnity revenue |  |  |  |  |  |
Distribution construction revenue |  | 1,436 |  |  |  |
Adjustment to expectation of cash flow from Financial assets of distribution concession to be indemnified |  | 16 |  |  |  |
Gain on inflation updating of concession grant fee |  | 347 |  |  |  |
Transactions in energy on the CCEE |  | 154 |  |  |  |
Mechanism for the sale of surplus |  | 234 |  |  |  |
Supply of gas |  | 2,011 |  |  |  |
Fine for violation of continuity indicator |  | (51) |  |  |  |
Other operating revenues |  | 1,709 | 1,721 |  | 1,585 |
Sector / Regulatory charges reported as Deductions from revenue |  | (11,722) |  |  |  |
NET REVENUE |  | 25,228 | 25,487 | [1] | 22,266 |
Restated [member] |  |  |  |  |  |
Disclosure of revenue [line items] |  |  |  |  |  |
Revenue from supply of energy |  |  | 26,928 |  |  |
Revenue from Use of Distribution Systems (the TUSD charge) |  |  | 2,722 |  | 2,045 |
CVA and Other financial components in tariff adjustment |  |  | 58 |  | 1,973 |
Reimbursement of PIS/Pasep and Cofins over ICMS credits to customers- realization |  |  | 1,428 |  |  |
Transmission operation and maintenance revenue |  |  | 352 |  | 343 |
Transmission construction revenue |  |  | 312 |  | 138 |
Interest revenue arising from the financing component in transmission contract asset |  |  | 328 |  |  |
Generation assets - indemnity revenue |  |  | 328 |  | 55 |
Transmission assets - indemnity revenue |  |  |  |  | 311 |
Distribution construction revenue |  |  | 980 |  | 802 |
Adjustment to expectation of cash flow from Financial assets of distribution concession to be indemnified |  |  | 18 |  |  |
Gain on inflation updating of concession grant fee |  |  | 318 |  | 321 |
Transactions in energy on the CCEE |  |  | 432 |  | 217 |
Supply of gas |  |  | 2,298 |  | 1,995 |
Fine for violation of continuity indicator |  |  | (58) |  | (44) |
Other operating revenues |  |  | 1,721 |  | 1,585 |
Sector / Regulatory charges reported as Deductions from revenue |  |  | (12,351) |  | (12,314) |
NET REVENUE | R$ 22,299 |  | 25,486 | [2],[3] | 22,299 | [2]
Operating Segments [member] | Elimination Segments [member] |  |  |  |  |  |
Disclosure of revenue [line items] |  |  |  |  |  |
Revenue from supply of energy |  | (79) |  |  |  |
Revenue from Use of Distribution Systems (the TUSD charge) |  | (24) |  |  |  |
Transmission operation and maintenance revenue |  | (226) |  |  |  |
Other operating revenues |  | (4) |  |  |  |
NET REVENUE |  | (333) | (307) |  |  |
Operating Segments [member] | Elimination Segments [member] | Restated [member] |  |  |  |  |  |
Disclosure of revenue [line items] |  |  |  |  |  |
Revenue from supply of energy |  |  | (76) |  | (78) |
Revenue from Use of Distribution Systems (the TUSD charge) |  |  | (25) |  | (22) |
CVA and Other financial components in tariff adjustment |  |  |  |  |  |
Reimbursement of PIS/Pasep and Cofins over ICMS credits to customers- realization |  |  |  |  |  |
Transmission operation and maintenance revenue |  |  | (198) |  | (177) |
Transmission construction revenue |  |  |  |  |  |
Transmission assets - indemnity revenue |  |  |  |  |  |
Distribution construction revenue |  |  |  |  |  |
Adjustment to expectation of cash flow from Financial assets of distribution concession to be indemnified |  |  |  |  |  |
Gain on inflation updating of concession grant fee |  |  |  |  |  |
Transactions in energy on the CCEE |  |  |  |  |  |
Supply of gas |  |  |  |  |  |
Fine for violation of continuity indicator |  |  |  |  |  |
Other operating revenues |  |  | (8) |  | (16) |
Sector / Regulatory charges reported as Deductions from revenue |  |  |  |  |  |
NET REVENUE |  |  | (307) |  | (293) |
Operating Segments [member] | Energy Generation Segment [member] |  |  |  |  |  |
Disclosure of revenue [line items] |  |  |  |  |  |
Revenue from supply of energy |  | 7,337 |  |  |  |
Gain on inflation updating of concession grant fee |  | 347 |  |  |  |
Transactions in energy on the CCEE |  | 154 |  |  |  |
Other operating revenues |  | 5 |  |  |  |
Sector / Regulatory charges reported as Deductions from revenue |  | (1,306) |  |  |  |
NET REVENUE |  | 6,537 | 6,882 |  |  |
Operating Segments [member] | Energy Generation Segment [member] | Restated [member] |  |  |  |  |  |
Disclosure of revenue [line items] |  |  |  |  |  |
Revenue from supply of energy |  |  | 7,037 |  | 7,065 |
Revenue from Use of Distribution Systems (the TUSD charge) |  |  |  |  |  |
CVA and Other financial components in tariff adjustment |  |  |  |  |  |
Reimbursement of PIS/Pasep and Cofins over ICMS credits to customers- realization |  |  | 414 |  |  |
Transmission operation and maintenance revenue |  |  |  |  |  |
Transmission construction revenue |  |  |  |  |  |
Generation assets - indemnity revenue |  |  |  |  | 55 |
Transmission assets - indemnity revenue |  |  |  |  |  |
Distribution construction revenue |  |  |  |  |  |
Adjustment to expectation of cash flow from Financial assets of distribution concession to be indemnified |  |  |  |  |  |
Gain on inflation updating of concession grant fee |  |  | 318 |  | 321 |
Transactions in energy on the CCEE |  |  | 439 |  | 217 |
Supply of gas |  |  |  |  |  |
Fine for violation of continuity indicator |  |  |  |  |  |
Other operating revenues |  |  | 82 |  | 82 |
Sector / Regulatory charges reported as Deductions from revenue |  |  | (1,408) |  | (1,366) |
NET REVENUE |  |  | 6,882 |  | 6,374 |
Operating Segments [member] | Energy Transmission Segment [member] |  |  |  |  |  |
Disclosure of revenue [line items] |  |  |  |  |  |
Transmission operation and maintenance revenue |  | 506 |  |  |  |
Transmission construction revenue |  | 201 |  |  |  |
Interest revenue arising from the financing component in transmission contract asset |  | 438 |  |  |  |
Other operating revenues |  | 34 |  |  |  |
Sector / Regulatory charges reported as Deductions from revenue |  | (436) |  |  |  |
NET REVENUE |  | 743 | 811 |  |  |
Operating Segments [member] | Energy Transmission Segment [member] | Restated [member] |  |  |  |  |  |
Disclosure of revenue [line items] |  |  |  |  |  |
Revenue from supply of energy |  |  |  |  |  |
Revenue from Use of Distribution Systems (the TUSD charge) |  |  |  |  |  |
CVA and Other financial components in tariff adjustment |  |  |  |  |  |
Reimbursement of PIS/Pasep and Cofins over ICMS credits to customers- realization |  |  |  |  |  |
Transmission operation and maintenance revenue |  |  | 550 |  | 520 |
Transmission construction revenue |  |  | 312 |  | 138 |
Interest revenue arising from the financing component in transmission contract asset |  |  | 328 |  | 311 |
Distribution construction revenue |  |  |  |  |  |
Adjustment to expectation of cash flow from Financial assets of distribution concession to be indemnified |  |  |  |  |  |
Gain on inflation updating of concession grant fee |  |  |  |  |  |
Transactions in energy on the CCEE |  |  |  |  |  |
Supply of gas |  |  |  |  |  |
Fine for violation of continuity indicator |  |  |  |  |  |
Other operating revenues |  |  | 28 |  | 29 |
Sector / Regulatory charges reported as Deductions from revenue |  |  | (407) |  | (290) |
NET REVENUE |  |  | 811 |  | 708 |
Operating Segments [member] | Energy Distribution Segment [member] |  |  |  |  |  |
Disclosure of revenue [line items] |  |  |  |  |  |
Revenue from supply of energy |  | 19,174 |  |  |  |
Revenue from Use of Distribution Systems (the TUSD charge) |  | 3,046 |  |  |  |
CVA and Other financial components in tariff adjustment |  | 455 |  |  |  |
Reimbursement of PIS/Pasep and Cofins over ICMS credits to customers- realization |  | 266 |  |  |  |
Distribution construction revenue |  | 1,385 |  |  |  |
Adjustment to expectation of cash flow from Financial assets of distribution concession to be indemnified |  | 16 |  |  |  |
Mechanism for the sale of surplus |  | 234 |  |  |  |
Fine for violation of continuity indicator |  | (51) |  |  |  |
Other operating revenues |  | 1,561 |  |  |  |
Sector / Regulatory charges reported as Deductions from revenue |  | (9,574) |  |  |  |
NET REVENUE |  | 16,512 | 15,919 |  |  |
Operating Segments [member] | Energy Distribution Segment [member] | Restated [member] |  |  |  |  |  |
Disclosure of revenue [line items] |  |  |  |  |  |
Revenue from supply of energy |  |  | 19,967 |  | 17,885 |
Revenue from Use of Distribution Systems (the TUSD charge) |  |  | 2,747 |  | 2,067 |
CVA and Other financial components in tariff adjustment |  |  | 58 |  | 1,973 |
Reimbursement of PIS/Pasep and Cofins over ICMS credits to customers- realization |  |  | 830 |  |  |
Transmission operation and maintenance revenue |  |  |  |  |  |
Transmission construction revenue |  |  |  |  |  |
Transmission assets - indemnity revenue |  |  |  |  |  |
Distribution construction revenue |  |  | 937 |  | 757 |
Adjustment to expectation of cash flow from Financial assets of distribution concession to be indemnified |  |  | 18 |  |  |
Gain on inflation updating of concession grant fee |  |  |  |  |  |
Transactions in energy on the CCEE |  |  | (7) |  |  |
Supply of gas |  |  |  |  |  |
Fine for violation of continuity indicator |  |  | (58) |  | (44) |
Other operating revenues |  |  | 1,468 |  | 1,345 |
Sector / Regulatory charges reported as Deductions from revenue |  |  | (10,041) |  | (10,226) |
NET REVENUE |  |  | 15,919 |  | 13,757 |
Operating Segments [member] | Gas Segment [member] |  |  |  |  |  |
Disclosure of revenue [line items] |  |  |  |  |  |
Distribution construction revenue |  | 51 |  |  |  |
Supply of gas |  | 2,011 |  |  |  |
Other operating revenues |  |  |  |  |  |
Sector / Regulatory charges reported as Deductions from revenue |  | (398) |  |  |  |
NET REVENUE |  | 1,664 | 1,858 |  |  |
Operating Segments [member] | Gas Segment [member] | Restated [member] |  |  |  |  |  |
Disclosure of revenue [line items] |  |  |  |  |  |
Revenue from supply of energy |  |  |  |  |  |
Revenue from Use of Distribution Systems (the TUSD charge) |  |  |  |  |  |
CVA and Other financial components in tariff adjustment |  |  |  |  |  |
Reimbursement of PIS/Pasep and Cofins over ICMS credits to customers- realization |  |  |  |  |  |
Transmission operation and maintenance revenue |  |  |  |  |  |
Transmission construction revenue |  |  |  |  |  |
Transmission assets - indemnity revenue |  |  |  |  |  |
Distribution construction revenue |  |  | 43 |  | 45 |
Adjustment to expectation of cash flow from Financial assets of distribution concession to be indemnified |  |  |  |  |  |
Gain on inflation updating of concession grant fee |  |  |  |  |  |
Transactions in energy on the CCEE |  |  |  |  |  |
Supply of gas |  |  | 2,298 |  | 1,995 |
Fine for violation of continuity indicator |  |  |  |  |  |
Other operating revenues |  |  |  |  |  |
Sector / Regulatory charges reported as Deductions from revenue |  |  | (483) |  | (421) |
NET REVENUE |  |  | 1,858 |  | 1,619 |
Operating Segments [member] | Other Segments [member] |  |  |  |  |  |
Disclosure of revenue [line items] |  |  |  |  |  |
Other operating revenues |  | 113 |  |  |  |
Sector / Regulatory charges reported as Deductions from revenue |  | (8) |  |  |  |
NET REVENUE |  | R$ 105 | 324 |  |  |
Operating Segments [member] | Other Segments [member] | Restated [member] |  |  |  |  |  |
Disclosure of revenue [line items] |  |  |  |  |  |
Revenue from supply of energy |  |  |  |  |  |
Revenue from Use of Distribution Systems (the TUSD charge) |  |  |  |  |  |
CVA and Other financial components in tariff adjustment |  |  |  |  |  |
Reimbursement of PIS/Pasep and Cofins over ICMS credits to customers- realization |  |  | 184 |  |  |
Transmission operation and maintenance revenue |  |  |  |  |  |
Transmission construction revenue |  |  |  |  |  |
Transmission assets - indemnity revenue |  |  |  |  |  |
Distribution construction revenue |  |  |  |  |  |
Adjustment to expectation of cash flow from Financial assets of distribution concession to be indemnified |  |  |  |  |  |
Gain on inflation updating of concession grant fee |  |  |  |  |  |
Transactions in energy on the CCEE |  |  |  |  |  |
Supply of gas |  |  |  |  |  |
Fine for violation of continuity indicator |  |  |  |  |  |
Other operating revenues |  |  | 151 |  | 145 |
Sector / Regulatory charges reported as Deductions from revenue |  |  | (12) |  | (11) |
NET REVENUE |  |  | R$ 323 |  | R$ 134 |
[1] | See note 2.8.
[2] | For further details of restatement of comparative balances, see Note 2.8
[3] | Recognition of the profit margin associated to the performance obligation to construct and upgrade the transmission infrastructure, as well as the interest revenue resulting from the financing component;

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

X
- Details
Name: | ifrs-full_SegmentsAxis=cig_TransmissionSegmentMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | ifrs-full_SegmentsAxis=cig_DistributionSegmentMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | ifrs-full_SegmentsAxis=cig_GasAndPowerSegmentMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | ifrs-full_SegmentsAxis=ifrs-full_AllOtherSegmentsMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |