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Property, Plant and Equipment - Summary of Accumulated Investments in Consortium (Detail) - BRL (R$) R$ in Millions | 12 Months Ended |
--- | --- | ---
Dec. 31, 2017 | Dec. 31, 2016 | Dec. 31, 2015 | Dec. 31, 2014
Disclosure of detailed information about property, plant and equipment [line items] |  |  |  |
Investment Property | R$ 618 | R$ 801 | R$ 861 | R$ 906
Average annual depreciation rate | 3.14% | 3.51% | 3.39% |
Cemig GT [member] |  |  |  |
Disclosure of detailed information about property, plant and equipment [line items] |  |  |  |
Investment Property | R$ 126 | R$ 127 |  |
Cemig GT [member] | Electricity Generation Consortium [member] | Investment Property Completed [member] | Gross Carrying Amount [member] | Queimado plant [member] |  |  |  |
Disclosure of detailed information about property, plant and equipment [line items] |  |  |  |
Investment Property | R$ 217 | R$ 217 |  |
Stake in energy generated | 82.50% |  |  |
Average annual depreciation rate |  | 4.00% |  |
Cemig GT [member] | Electricity Generation Consortium [member] | Investment Property Completed [member] | Gross Carrying Amount [member] | Accumulated Depreciation and Amortisation [member] |  |  |  |
Disclosure of detailed information about property, plant and equipment [line items] |  |  |  |
Investment Property | R$ (91) | R$ (90) |  |

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- Definition Expiry date 2019-01-01: The amount of property (land or a building - or part of a building - or both) held (by the owner or by the lessee under a finance lease) to earn rentals or for capital appreciation or both, rather than for: (a) use in the production or supply of goods or services or for administrative purposes; or (b) sale in the ordinary course of business. Effective 2019-01-01: The amount of property (land or a building - or part of a building - or both) held (by the owner or by the lessee as a right-of-use asset) to earn rentals or for capital appreciation or both, rather than for: (a) use in the production or supply of goods or services or for administrative purposes; or (b) sale in the ordinary course of business. + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Name IAS -Number 40 -IssueDate 2017-01-01 -Paragraph 76 -URI http://eifrs.ifrs.org/eifrs/XBRL?type=IAS&num=40&date=2017-03-01&anchor=para_76&doctype=Standard -URIDate 2017-03-09 Reference 2: http://www.xbrl.org/2003/role/disclosureRef -Name IAS -Number 40 -IssueDate 2017-01-01 -Paragraph 79 -Subparagraph d -URI http://eifrs.ifrs.org/eifrs/XBRL?type=IAS&num=40&date=2017-03-01&anchor=para_79_d&doctype=Standard -URIDate 2017-03-09 Reference 3: http://www.xbrl.org/2003/role/disclosureRef -Name IAS -Number 1 -IssueDate 2017-01-01 -Paragraph 54 -Subparagraph b -URI http://eifrs.ifrs.org/eifrs/XBRL?type=IAS&num=1&date=2017-03-01&anchor=para_54_b&doctype=Standard -URIDate 2017-03-09 + Details
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