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18. INTANGIBLE ASSETS (Details) - BRL (R$) R$ in Millions | Dec. 31, 2020 | Dec. 31, 2019 | Dec. 31, 2018 | Dec. 31, 2017
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Disclosure of detailed information about intangible assets [line items] |  |  |  |  |  |  |
Intangible assets |  | R$ 11,810 |  | R$ 11,624 | [1] | R$ 10,777 | R$ 11,156
Temporary Easements Intangible Assets [member] |  |  |  |  |  |  |
Disclosure of detailed information about intangible assets [line items] |  |  |  |  |  |  |
Intangible assets |  | 9 |  | 9 |  | 8 |
Onerous Concession [member] |  |  |  |  |  |  |
Disclosure of detailed information about intangible assets [line items] |  |  |  |  |  |  |
Intangible assets |  | 6 |  | 7 |  | 7 |
Assets Of Concession [member] |  |  |  |  |  |  |
Disclosure of detailed information about intangible assets [line items] |  |  |  |  |  |  |
Intangible assets |  | 11,674 | [2] | 11,517 | [2] | 10,680 |
Other Intangible Assets [member] |  |  |  |  |  |  |
Disclosure of detailed information about intangible assets [line items] |  |  |  |  |  |  |
Intangible assets |  | 8 |  | 10 |  | 18 |
Intangible Assets Under Development [member] |  |  |  |  |  |  |
Disclosure of detailed information about intangible assets [line items] |  |  |  |  |  |  |
Intangible assets |  | 113 |  | 82 |  |  |
Useful Life Defined Intangible Asset [member] |  |  |  |  |  |  |
Disclosure of detailed information about intangible assets [line items] |  |  |  |  |  |  |
Intangible assets |  | 11,697 |  | 11,542 |  | R$ 10,714 |
Temporary Easement Intangible Assets [member] |  |  |  |  |  |  |
Disclosure of detailed information about intangible assets [line items] |  |  |  |  |  |  |
Intangible assets |  |  |  | 8 |  |  |
Historical cost [member] |  |  |  |  |  |  |
Disclosure of detailed information about intangible assets [line items] |  |  |  |  |  |  |
Intangible assets |  | 21,004 |  | 20,230 |  |  |
Historical cost [member] | Onerous Concession [member] |  |  |  |  |  |  |
Disclosure of detailed information about intangible assets [line items] |  |  |  |  |  |  |
Intangible assets |  | 19 |  | 20 |  |  |
Historical cost [member] | Assets Of Concession [member] |  |  |  |  |  |  |
Disclosure of detailed information about intangible assets [line items] |  |  |  |  |  |  |
Intangible assets | [2] | 20,781 |  | 20,039 |  |  |
Historical cost [member] | Other Intangible Assets [member] |  |  |  |  |  |  |
Disclosure of detailed information about intangible assets [line items] |  |  |  |  |  |  |
Intangible assets |  | 78 |  | 77 |  |  |
Historical cost [member] | Intangible Assets Under Development [member] |  |  |  |  |  |  |
Disclosure of detailed information about intangible assets [line items] |  |  |  |  |  |  |
Intangible assets |  | 20,891 |  | 82 |  |  |
Historical cost [member] | Useful Life Defined Intangible Asset [member] |  |  |  |  |  |  |
Disclosure of detailed information about intangible assets [line items] |  |  |  |  |  |  |
Intangible assets |  | 113 |  | 20,148 |  |  |
Historical cost [member] | Temporary Easement Intangible Assets [member] |  |  |  |  |  |  |
Disclosure of detailed information about intangible assets [line items] |  |  |  |  |  |  |
Intangible assets |  | 13 |  | 12 |  |  |
Accumulated depreciation and amortisation [member] |  |  |  |  |  |  |
Disclosure of detailed information about intangible assets [line items] |  |  |  |  |  |  |
Intangible assets |  |  |  | (8,606) |  |  |
Accumulated depreciation and amortisation [member] | Onerous Concession [member] |  |  |  |  |  |  |
Disclosure of detailed information about intangible assets [line items] |  |  |  |  |  |  |
Intangible assets |  | (13) |  | (13) |  |  |
Accumulated depreciation and amortisation [member] | Assets Of Concession [member] |  |  |  |  |  |  |
Disclosure of detailed information about intangible assets [line items] |  |  |  |  |  |  |
Intangible assets | [2] | (9,107) |  | (8,522) |  |  |
Accumulated depreciation and amortisation [member] | Other Intangible Assets [member] |  |  |  |  |  |  |
Disclosure of detailed information about intangible assets [line items] |  |  |  |  |  |  |
Intangible assets |  | (70) |  | (67) |  |  |
Accumulated depreciation and amortisation [member] | Useful Life Defined Intangible Asset [member] |  |  |  |  |  |  |
Disclosure of detailed information about intangible assets [line items] |  |  |  |  |  |  |
Intangible assets |  | (9,194) |  | (8,606) |  |  |
Accumulated depreciation and amortisation [member] | Temporary Easement Intangible Assets [member] |  |  |  |  |  |  |
Disclosure of detailed information about intangible assets [line items] |  |  |  |  |  |  |
Intangible assets |  | R$ (4) |  | R$ (4) |  |  |
[1] | See note 2.8.
[2] | The rights of authorization to generate wind power granted to the subsidiary Parajuru and Volta do Rio, at the net value of R$128, and of the gas distribution concession, granted to Gasmig, valued at R$412, are classified in the consolidated statement of financial position under intangibles assets and are amortized by the straight-line method, for the period of the concessions.

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