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Loans, Financings and Debentures - Summary of Loans Financing and Debentures (Detail) € in Millions, R$ in Millions | 12 Months Ended |  |
--- | --- | --- | ---
Dec. 31, 2017 BRL (R$) | Dec. 31, 2017 EUR (€) | Dec. 31, 2016 BRL (R$) | Dec. 31, 2016 EUR (€)
Disclosure of detailed information about borrowings [line items] |  |  |  |
Current |  | € 2,371 |  |
Current | R$ | R$ 2,371 |  |  |
2017 Non-current |  | 12,027 |  |
Non-current | R$ | 12,027 |  | R$ 10,342 |
Total |  | 14,398 |  | € 15,179
Total | R$ | 14,398 |  | 15,179 |
Interest paid in advance [member] |  |  |  |
Disclosure of detailed information about borrowings [line items] |  |  |  |
2017 Non-current | (48) | (48) |  |
Total | (48) | (48) |  |
Debt in Foreign Currency [member] |  |  |  |
Disclosure of detailed information about borrowings [line items] |  |  |  |
Current | 31 | 31 |  |
2017 Non-current | 3,267 | 3,267 |  |
Total | R$ 3,298 | 3,298 | 30 | 30
TJLP Plus Two Point Three Four [member] |  |  |  |
Disclosure of detailed information about borrowings [line items] |  |  |  |
Principal maturity | 2017 |  |  |
Annual financial cost | TJLP+2.34% |  |  |
Currency | R$ |  |  |
Total |  |  | 74 | 74
Debt in Brazilian currency [member] |  |  |  |
Disclosure of detailed information about borrowings [line items] |  |  |  |
Current | R$ 151 | 151 |  |
2017 Non-current | 1,920 | 1,920 |  |
Total | 2,071 | 2,071 | 3,729 | 3,729
Loans and Financings [member] |  |  |  |
Disclosure of detailed information about borrowings [line items] |  |  |  |
Current | 182 | 182 |  |
2017 Non-current | 5,187 | 5,187 |  |
Total | R$ 5,369 | 5,369 | 3,759 | 3,759
Transaction costs [member] |  |  |  |
Disclosure of detailed information about borrowings [line items] |  |  |  |
Current |  | (2) |  |
2017 Non-current |  | (48) |  |
Total |  | (50) |  | (79)
KfW (Cemig GT) [member] |  |  |  |
Disclosure of detailed information about borrowings [line items] |  |  |  |
Principal maturity | 2019 |  |  |
Annual financial cost | 178 |  |  |
Currency | Euros |  |  |
Current |  | 4 |  |
Total |  | 4 |  | 7
Eurobonds [member] |  |  |  |
Disclosure of detailed information about borrowings [line items] |  |  |  |
Principal maturity | 2024 |  |  |
Annual financial cost | 9.25 |  |  |
Currency | USD |  |  |
Current | R$ 25 | 25 |  |
2017 Non-current | 3,308 | 3,308 |  |
Total | R$ 3,333 | 3,333 |  |
Banco do Brasil (Cemig GT) [member] | One Zero Eight Point Three Three Percent of Interbank Rate for Certificates of Deposit [member] |  |  |  |
Disclosure of detailed information about borrowings [line items] |  |  |  |
Principal maturity | 2017 |  |  |
Annual financial cost | 108.33% of the CDI Rate |  |  |
Currency | R$ |  |  |
Total |  |  | 73 | 73
Banco do Brasil (Cemig GT) [member] | One Zero Eight Point Zero Zero Percent of Interbank Rate for Certificates of Deposit [member] |  |  |  |
Disclosure of detailed information about borrowings [line items] |  |  |  |
Principal maturity | 2017 |  |  |
Annual financial cost | 108.00% of CDI |  |  |
Currency | R$ |  |  |
Total |  |  | 151 | 151
Banco do Brasil (Cemig GT) [member] | One One One Point Zero Zero Percent of Interbank Rate for Certificates of Deposit [member] |  |  |  |
Disclosure of detailed information about borrowings [line items] |  |  |  |
Principal maturity | 2017 |  |  |
Annual financial cost | 111.00% of CDI Rate |  |  |
Currency | R$ |  |  |
Total |  |  | 51 | 51
Banco do Brasil (Cemig GT) [member] | One four zero point zero percent of interbank rate for certificates of deposit [member] |  |  |  |
Disclosure of detailed information about borrowings [line items] |  |  |  |
Principal maturity | 2021 |  |  |
Annual financial cost | 140.00% of CDI Rate |  |  |
Currency | R$ |  |  |
Current | R$ 1 | 1 |  |
2017 Non-current | 741 | 741 |  |
Total | R$ 742 | 742 | 1,156 | 1,156
Banco do Brasil (Cemig GT) [member] | One four six point five zero percent of interbank rate for certificates of deposit [member] |  |  |  |
Disclosure of detailed information about borrowings [line items] |  |  |  |
Principal maturity | 2022 |  |  |
Annual financial cost | 146.50% of CDI |  |  |
Currency | R$ |  |  |
2017 Non-current | R$ 500 | 500 |  |
Total | R$ 500 | 500 | 510 | 510
CEF [member] | One four six point five zero percent of interbank rate for certificates of deposit [member] |  |  |  |
Disclosure of detailed information about borrowings [line items] |  |  |  |
Principal maturity | 2022 |  |  |
Annual financial cost | 146.50% of CDI |  |  |
Currency | R$ |  |  |
Current | R$ 1 | 1 |  |
2017 Non-current | 626 | 626 |  |
Total | R$ 627 | 627 | 698 | 698
CEF [member] | One One Nine Point Zero Zero Percent of interbank rate for certificates of deposit [member] |  |  |  |
Disclosure of detailed information about borrowings [line items] |  |  |  |
Principal maturity | 2018 |  |  |
Annual financial cost | 119.00% of CDI |  |  |
Currency | R$ |  |  |
Current | R$ 8 | 8 |  |
Total | R$ 8 | 8 | 109 | 109
Eletrobras [member] |  |  |  |
Disclosure of detailed information about borrowings [line items] |  |  |  |
Principal maturity | 2023 |  |  |
Annual financial cost | UFIR; RGR + 6.00 to 8.00% |  |  |
Currency | R$ |  |  |
Current | R$ 17 | 17 |  |
2017 Non-current | 33 | 33 |  |
Total | R$ 50 | 50 | 68 | 68
Large Consumers [member] | Various [member] |  |  |  |
Disclosure of detailed information about borrowings [line items] |  |  |  |
Principal maturity | 2024 |  |  |
Annual financial cost | Various |  |  |
Currency | R$ |  |  |
Current | R$ 2 | 2 |  |
2017 Non-current | 2 | 2 |  |
Total | R$ 4 | 4 | 6 | 6
FINEP [member] | Tjlp plus five and tjlp plus two point five [member] |  |  |  |
Disclosure of detailed information about borrowings [line items] |  |  |  |
Principal maturity | 2018 |  |  |
Annual financial cost | TJLP + 5% and TJLP + 8% |  |  |
Currency | R$ |  |  |
Current | R$ 2 | 2 |  |
Total | R$ 2 | 2 | 6 | 6
Promissory Notes - Cemig GT - 7th Issue [member] | One two eight point zero zero of interbank rate for certificates of deposit [member] |  |  |  |
Disclosure of detailed information about borrowings [line items] |  |  |  |
Principal maturity | 2017 |  |  |
Annual financial cost | 128.00% of CDI |  |  |
Currency | R$ |  |  |
Total |  |  | 674 | 674
Banco da amazonia [member] | Interbank rate for certificates of deposit plus one point nine zero [member] |  |  |  |
Disclosure of detailed information about borrowings [line items] |  |  |  |
Principal maturity | 2018 |  |  |
Annual financial cost | CDI + 1.90% |  |  |
Currency | R$ |  |  |
Current | R$ 122 | 122 |  |
Total | R$ 122 | 122 | 123 | 123
Sonda (Cemig Telecom) [member] | One one zero percent of interbank rate for certificates of deposit [member] |  |  |  |
Disclosure of detailed information about borrowings [line items] |  |  |  |
Principal maturity | 2021 |  |  |
Annual financial cost | 110.00% of CDI |  |  |
Currency | R$ |  |  |
2017 Non-current | R$ 42 | 42 |  |
Total | 42 | 42 | 83 | 83
Transaction costs [member] |  |  |  |
Disclosure of detailed information about borrowings [line items] |  |  |  |
Current | (2) | (2) |  |
2017 Non-current | (24) | (24) |  |
Total | (26) | (26) | (53) | (53)
Total | R$ | (50) |  | (79) |
Transaction costs [member] | Transaction costs [member] |  |  |  |
Disclosure of detailed information about borrowings [line items] |  |  |  |
Current | R$ | (2) |  |  |
Non-current | R$ | (48) |  |  |
Total | R$ | R$ (50) |  | (79) |
Debentures-3rd Issue, 1st Series [member] | Interbank rate for certificates of deposit plus zero point nine zero [member] |  |  |  |
Disclosure of detailed information about borrowings [line items] |  |  |  |
Principal maturity | 2017 |  |  |
Annual financial cost | CDI + 0.90% |  |  |
Currency | R$ |  |  |
Total | R$ |  |  | 543 |
Total |  |  |  | 543
Debentures-3rd Issue, 1st Series [member] | Interbank rate for certificates of deposit plus zero point six nine [member] |  |  |  |
Disclosure of detailed information about borrowings [line items] |  |  |  |
Principal maturity | 2018 |  |  |
Annual financial cost | CDI + 0.69% |  |  |
Currency | R$ |  |  |
Current | R$ | R$ 447 |  |  |
Current |  | 447 |  |
Total | R$ | R$ 447 |  | 464 |
Total |  | 447 |  | 464
Debentures-3rd Issue, 2nd Series [member] | Ipca plus six point zero zero [member] |  |  |  |
Disclosure of detailed information about borrowings [line items] |  |  |  |
Principal maturity | 2019 |  |  |
Annual financial cost | IPCA + 6.00% |  |  |
Currency | R$ |  |  |
Current | R$ | R$ 158 |  |  |
Current |  | 158 |  |
Non-current | R$ | 143 |  |  |
2017 Non-current |  | 143 |  |
Total | R$ | R$ 301 |  | 293 |
Total |  | 301 |  | 293
Debentures-3rd Issue, 2nd Series [member] | Ipca plus four point seven zero [member] |  |  |  |
Disclosure of detailed information about borrowings [line items] |  |  |  |
Principal maturity | 2021 |  |  |
Annual financial cost | IPCA + 4.70% |  |  |
Currency | R$ |  |  |
Current | R$ | R$ 59 |  |  |
Current |  | 59 |  |
Non-current | R$ | 1,478 |  |  |
2017 Non-current |  | 1,478 |  |
Total | R$ | R$ 1,537 |  | 1,496 |
Total |  | 1,537 |  | 1,496
Debentures-3rd Issue, 3rd Series [member] | Ipca plus six point two zero [member] |  |  |  |
Disclosure of detailed information about borrowings [line items] |  |  |  |
Principal maturity | 2022 |  |  |
Annual financial cost | IPCA + 6.20% |  |  |
Currency | R$ |  |  |
Current | R$ | R$ 51 |  |  |
Current |  | 51 |  |
Non-current | R$ | 960 |  |  |
2017 Non-current |  | 960 |  |
Total | R$ | R$ 1,011 |  | 984 |
Total |  | 1,011 |  | 984
Debentures-3rd Issue, 3rd Series [member] | Ipca plus five point one zero [member] |  |  |  |
Disclosure of detailed information about borrowings [line items] |  |  |  |
Principal maturity | 2025 |  |  |
Annual financial cost | IPCA + 5.10% |  |  |
Currency | R$ |  |  |
Current | R$ | R$ 39 |  |  |
Current |  | 39 |  |
Non-current | R$ | 882 |  |  |
2017 Non-current |  | 882 |  |
Total | R$ | R$ 921 |  | 896 |
Total |  | 921 |  | 896
Debentures-5th Issue, 1st Series [member] | Interbank rate for certificates of deposit plus one point seven zero [Member] |  |  |  |
Disclosure of detailed information about borrowings [line items] |  |  |  |
Principal maturity | 2018 |  |  |
Annual financial cost | CDI + 1.70% |  |  |
Currency | R$ |  |  |
Current | R$ | R$ 703 |  |  |
Current |  | 703 |  |
Total | R$ | R$ 703 |  | 1,411 |
Total |  | 703 |  | 1,411
Debentures sixth issue first series [member] | Interbank rate for certificates of deposit plus one point six zero [Member] |  |  |  |
Disclosure of detailed information about borrowings [line items] |  |  |  |
Principal maturity | 2018 |  |  |
Annual financial cost | CDI + 1.60% |  |  |
Currency | R$ |  |  |
Current | R$ | R$ 508 |  |  |
Current |  | 508 |  |
Total | R$ | R$ 508 |  | 1,041 |
Total |  | 508 |  | 1,041
Debentures sixth issue first series [member] | Ipca plus eight point zero seven [Member] |  |  |  |
Disclosure of detailed information about borrowings [line items] |  |  |  |
Principal maturity | 2020 |  |  |
Annual financial cost | IPCA +8.07% |  |  |
Currency | R$ |  |  |
Current | R$ | R$ 1 |  |  |
Current |  | 1 |  |
Non-current | R$ | 31 |  |  |
2017 Non-current |  | 31 |  |
Total | R$ | R$ 32 |  | 31 |
Total |  | 32 |  | 31
Debentures-7th Issue, 1st Series [member] | One four zero point zero percent of interbank rate for certificates of deposit [member] |  |  |  |
Disclosure of detailed information about borrowings [line items] |  |  |  |
Principal maturity | 2021 |  |  |
Annual financial cost | 140.00% of CDI |  |  |
Currency | R$ |  |  |
Current | R$ | R$ 47 |  |  |
Current |  | 47 |  |
Non-current | R$ | 1,636 |  |  |
2017 Non-current |  | 1,636 |  |
Total | R$ | R$ 1,683 |  | 2,242 |
Total |  | 1,683 |  | 2,242
Debentures, 2nd Issue [member] | Ipca plus seven point nine six [Member] |  |  |  |
Disclosure of detailed information about borrowings [line items] |  |  |  |
Principal maturity | 2017 |  |  |
Annual financial cost | IPCA + 7.96% |  |  |
Currency | R$ |  |  |
Total | R$ |  |  | 235 |
Total |  |  |  | 235
Debentures fourth issue first series [member] | One four six point five zero percent of interbank rate for certificates of deposit [member] |  |  |  |
Disclosure of detailed information about borrowings [line items] |  |  |  |
Principal maturity | 2022 |  |  |
Annual financial cost | 146.50% of CDI |  |  |
Currency | R$ |  |  |
Current | R$ | R$ 1 |  |  |
Current |  | 1 |  |
Non-current | R$ | 1,575 |  |  |
2017 Non-current |  | 1,575 |  |
Total | R$ | R$ 1,576 |  |  |
Total |  | 1,576 |  |
Debentures fourth issue first series [member] | Interbank rate for certificates of deposit plus four point zero five percentage one [member] |  |  |  |
Disclosure of detailed information about borrowings [line items] |  |  |  |
Principal maturity | 2018 |  |  |
Annual financial cost | CDI + 4.05% |  |  |
Currency | R$ |  |  |
Current | R$ | R$ 20 |  |  |
Current |  | 20 |  |
Total | R$ | 20 |  | 1,627 |
Total |  | 20 |  | 1,627
Debentures [member] |  |  |  |
Disclosure of detailed information about borrowings [line items] |  |  |  |
Total | R$ | R$ 9,029 |  | 11,420 |
Debentures [member] | CDI + 1.60 [member] |  |  |  |
Disclosure of detailed information about borrowings [line items] |  |  |  |
Principal maturity | 2018 |  |  |
Annual financial cost | CDI + 1.60% |  |  |
Currency | R$ |  |  |
Current | R$ | R$ 100 |  |  |
Current |  | 100 |  |
Total | R$ | R$ 100 |  | 101 |
Total |  | 100 |  | 101
Debentures [member] | Interbank rate for certificates of deposit plus zero point seven four [member] |  |  |  |
Disclosure of detailed information about borrowings [line items] |  |  |  |
Principal maturity | 2018 |  |  |
Annual financial cost | CDI + 0.74% |  |  |
Currency | R$ |  |  |
Current | R$ | R$ 34 |  |  |
Current |  | 34 |  |
Total | R$ | R$ 34 |  | 67 |
Total |  | 34 |  | 67
Debentures [member] | Tjlp plus one point eight two percentage selic plus one point eight two percentage [member] |  |  |  |
Disclosure of detailed information about borrowings [line items] |  |  |  |
Principal maturity | 2022 |  |  |
Annual financial cost | TJLP+1.82% (75%); Selic+1.82% (25%) |  |  |
Currency | R$ |  |  |
Current | R$ | R$ 33 |  |  |
Current |  | 33 |  |
Non-current | R$ | 122 |  |  |
2017 Non-current |  | 122 |  |
Total | R$ | R$ 155 |  | 133 |
Total |  | 155 |  | 133
Debentures [member] | One one six point five zero percent of inter bank rate for certificates of deposit [member] |  |  |  |
Disclosure of detailed information about borrowings [line items] |  |  |  |
Principal maturity | 2019 |  |  |
Annual financial cost | 116.50% of CDI |  |  |
Currency | R$ |  |  |
Non-current | R$ | R$ 50 |  |  |
2017 Non-current |  | 50 |  |
Total | R$ | R$ 50 |  |  |
Total |  | 50 |  |
Debentures [member] | One two eight point five zero percent of inter bank rate for certificates of deposit [member] |  |  |  |
Disclosure of detailed information about borrowings [line items] |  |  |  |
Principal maturity | 2019 |  |  |
Annual financial cost | 128.50% of CDI |  |  |
Currency | R$ |  |  |
Current | R$ | R$ 15 |  |  |
Current |  | 15 |  |
Non-current | R$ | 11 |  |  |
2017 Non-current |  | 11 |  |
Total | R$ | 26 |  |  |
Total |  | 26 |  |
Subsidiary Securities [member] |  |  |  |
Disclosure of detailed information about borrowings [line items] |  |  |  |
Current | R$ | (25) |  |  |
Current |  | (25) |  |
Total | R$ | (25) |  | (65) |
Total |  | (25) |  | (65)
Total | R$ | (25) |  | (65) |
Net debentures [member] |  |  |  |
Disclosure of detailed information about borrowings [line items] |  |  |  |
Current | R$ | 2,189 |  |  |
Current |  | 2,189 |  |
Non-current | R$ | 6,840 |  |  |
2017 Non-current |  | 6,840 |  |
Total | R$ | R$ 9,029 |  | R$ 11,420 |
Total |  | 9,029 |  | 11,420
Debt in Foreign Currency [member] | Banco do Brasil (Cemig GT) [member] | Various [member] |  |  |  |
Disclosure of detailed information about borrowings [line items] |  |  |  |
Principal maturity | 2024 |  |  |
Annual financial cost | Various |  |  |
Currency | US$ |  |  |
Current |  | 2 |  |
2017 Non-current |  | 22 |  |
Total |  | 24 |  | € 23
Transaction costs [member] |  |  |  |
Disclosure of detailed information about borrowings [line items] |  |  |  |
2017 Non-current | R$ (15) | (15) |  |
Total | R$ (15) | € (15) |  |

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- Definition The amount of outstanding funds that the entity is obligated to repay. + References Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef -Name IAS -Number 1 -IssueDate 2017-01-01 -Paragraph 55 -URI http://eifrs.ifrs.org/eifrs/XBRL?type=IAS&num=1&date=2017-03-01&anchor=para_55&doctype=Standard -URIDate 2017-03-09 + Details
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- Definition The currency in which the borrowings are denominated. [Refer: Borrowings] + References Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef -Name IFRS -Number 7 -IssueDate 2017-01-01 -Paragraph 7 -URI http://eifrs.ifrs.org/eifrs/XBRL?type=IFRS&num=7&date=2017-03-01&anchor=para_7&doctype=Standard -URIDate 2017-03-09 + Details
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- Definition The amount of current borrowings and current portion of non-current borrowings. [Refer: Borrowings] + References Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef -Name IAS -Number 1 -IssueDate 2017-01-01 -Paragraph 55 -URI http://eifrs.ifrs.org/eifrs/XBRL?type=IAS&num=1&date=2017-03-01&anchor=para_55&doctype=Standard -URIDate 2017-03-09 + Details
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- Definition The amount of current loans received and the current portion of non-current loans received. [Refer: Loans received] + References Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef -Name IAS -Number 1 -IssueDate 2017-01-01 -Paragraph 112 -Subparagraph c -URI http://eifrs.ifrs.org/eifrs/XBRL?type=IAS&num=1&date=2017-03-01&anchor=para_112_c&doctype=Standard -URIDate 2017-03-09 + Details
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- Definition The amount of current notes and debentures issued and the current portion of non-current notes and debentures issued. [Refer: Notes and debentures issued] + References Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef -Name IAS -Number 1 -IssueDate 2017-01-01 -Paragraph 112 -Subparagraph c -URI http://eifrs.ifrs.org/eifrs/XBRL?type=IAS&num=1&date=2017-03-01&anchor=para_112_c&doctype=Standard -URIDate 2017-03-09 + Details
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- Definition The amount of loans received. + References Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef -Name IAS -Number 1 -IssueDate 2017-01-01 -Paragraph 112 -Subparagraph c -URI http://eifrs.ifrs.org/eifrs/XBRL?type=IAS&num=1&date=2017-03-01&anchor=para_112_c&doctype=Standard -URIDate 2017-03-09 + Details
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- Definition The non-current portion of non-current borrowings. [Refer: Borrowings] + References Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef -Name IAS -Number 1 -IssueDate 2017-01-01 -Paragraph 55 -URI http://eifrs.ifrs.org/eifrs/XBRL?type=IAS&num=1&date=2017-03-01&anchor=para_55&doctype=Standard -URIDate 2017-03-09 + Details
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- Definition The non-current portion of non-current loans received. [Refer: Loans received] + References Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef -Name IAS -Number 1 -IssueDate 2017-01-01 -Paragraph 112 -Subparagraph c -URI http://eifrs.ifrs.org/eifrs/XBRL?type=IAS&num=1&date=2017-03-01&anchor=para_112_c&doctype=Standard -URIDate 2017-03-09 + Details
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