XML 224 R217.htm IDEA: XBRL DOCUMENT
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Subsequent Events - Additional Information (Detail) - BRL (R$) |  |  |  |  | 1 Months Ended | 3 Months Ended |  |  |  |
--- | --- | --- | --- | --- | --- | --- | --- | --- | --- | ---
Apr. 23, 2018 | Mar. 31, 2018 | Mar. 21, 2018 | Oct. 26, 2017 | Jan. 05, 2018 | Mar. 31, 2018 | May 03, 2018 | Dec. 31, 2017 | Dec. 31, 2016 | Dec. 31, 2015
Disclosure of non-adjusting events after reporting period [line items] |  |  |  |  |  |  |  |  |  |
Number of shares issued |  |  |  |  |  |  |  | 1,258,841,654 | 1,258,841,654 | 1,258,841,654
Capital increase | R$ 1,000,000,000 |  |  | R$ 1,000,000,000 |  |  |  |  |  |
New shares authorized | 199,910,947 |  |  | 199,910,947 |  |  |  |  |  |
Par value per share | R$ 5.00 |  |  | R$ 5.00 |  |  |  |  |  |
Proceeds from issuance capital | R$ 1,324,000,000 |  |  |  |  |  |  |  |  |
Capital reserve | R$ 324,000,000 |  |  |  |  |  |  | R$ 1,925,000,000 | R$ 1,925,000,000 | R$ 1,925,000,000
Preference shares [member] |  |  |  |  |  |  |  |  |  |
Disclosure of non-adjusting events after reporting period [line items] |  |  |  |  |  |  |  |  |  |
Number of shares issued |  |  |  |  |  |  |  | 838,076,946 | 838,076,946 | 838,076,946
New shares authorized | 133,061,442 |  |  | 133,061,442 |  |  |  |  |  |
Par value per share |  |  |  | R$ 6.57 |  |  |  |  |  |
Common shares [member] |  |  |  |  |  |  |  |  |  |
Disclosure of non-adjusting events after reporting period [line items] |  |  |  |  |  |  |  |  |  |
Number of shares issued |  |  |  |  |  |  |  | 420,764,708 | 420,764,708 | 420,764,708
New shares authorized | 66,849,505 |  |  | 66,849,505 |  |  |  |  |  |
Par value per share |  |  |  | R$ 6.57 |  |  |  |  |  |
Chipley [member] |  |  |  |  |  |  |  |  |  |
Disclosure of non-adjusting events after reporting period [line items] |  |  |  |  |  |  |  |  |  |
Percentage of shares to be acquired |  |  |  |  |  |  | 100.00% |  |  |
Renova [member] |  |  |  |  |  |  |  |  |  |
Disclosure of non-adjusting events after reporting period [line items] |  |  |  |  |  |  |  |  |  |
Percentage of shares to be acquired |  |  |  |  |  |  | 51.00% |  |  |
Bottom of range [member] |  |  |  |  |  |  |  |  |  |
Disclosure of non-adjusting events after reporting period [line items] |  |  |  |  |  |  |  |  |  |
Capital increase | R$ 6,294,000,000 |  |  |  |  |  |  |  |  |
Top of range [member] |  |  |  |  |  |  |  |  |  |
Disclosure of non-adjusting events after reporting period [line items] |  |  |  |  |  |  |  |  |  |
Capital increase | R$ 7,294,000,000 |  |  |  |  |  |  |  |  |
Promissory Notes [member] |  |  |  |  |  |  |  |  |  |
Disclosure of non-adjusting events after reporting period [line items] |  |  |  |  |  |  |  |  |  |
Borrowings |  |  |  |  | R$ 400,000,000 |  |  |  |  |
Debt instrument interest rate |  |  |  |  | 151.00% |  |  |  |  |
Entering into significant commitments or contingent liabilities [member] |  |  |  |  |  |  |  |  |  |
Disclosure of non-adjusting events after reporting period [line items] |  |  |  |  |  |  |  |  |  |
Financial volume from stock issuance |  |  | R$ 111,000,000 |  |  |  |  |  |  |
Entering into significant commitments or contingent liabilities [member] | Ordinary shares [member] |  |  |  |  |  |  |  |  |  |
Disclosure of non-adjusting events after reporting period [line items] |  |  |  |  |  |  |  |  |  |
Number of shares issued |  |  | 13,139,799 |  |  |  |  |  |  |
Average price per share |  |  | R$ 7.30 |  |  |  |  |  |  |
Share price |  |  | R$ 96,000,000 |  |  |  |  |  |  |
Entering into significant commitments or contingent liabilities [member] | Preference shares [member] |  |  |  |  |  |  |  |  |  |
Disclosure of non-adjusting events after reporting period [line items] |  |  |  |  |  |  |  |  |  |
Number of shares issued |  |  | 1,815,750 |  |  |  |  |  |  |
Average price per share |  |  | R$ 8.22 |  |  |  |  |  |  |
Share price |  |  | R$ 15,000,000 |  |  |  |  |  |  |
Entering into significant commitments or contingent liabilities [member] | Ceming GT [Member] |  |  |  |  |  |  |  |  |  |
Disclosure of non-adjusting events after reporting period [line items] |  |  |  |  |  |  |  |  |  |
Advanced payment for power supply |  |  |  |  |  | R$ 71,000,000 |  |  |  |
Entering into significant commitments or contingent liabilities [member] | Ceming GT [Member] | Interbank deposit certificate CDI rate [member] |  |  |  |  |  |  |  |  |  |
Disclosure of non-adjusting events after reporting period [line items] |  |  |  |  |  |  |  |  |  |
Advanced discount percentage |  |  |  |  |  | 155.00% |  |  |  |
Entering into significant commitments or contingent liabilities [member] | Two Thousand Eighteen Employee Voluntary Severance Program [Member] |  |  |  |  |  |  |  |  |  |
Disclosure of non-adjusting events after reporting period [line items] |  |  |  |  |  |  |  |  |  |
Description of type of retirement benefit plan |  | In March 2018, the Company approved the Programmed Voluntary Retirement Program (‘the 2018 PDVP’). Employees eligible to be part of the program are those will have worked for Cemig for 25 years or more by December 31, 2018. The period for joining the program was April 2 through 30, 2018. The program offers payment of the severance amounts specified by law, including payment for notice period, and especial deposit of the ‘penalty’ amount of 40% of the FGTS (Labour Guarantee Fund) Base Value, and other charges specified by the legislation, with no provision for the payment of any additional amounts. |  |  |  |  |  |  |  |
Description of eligible employees to take part of plan |  | Employees eligible to be part of the program are those will have worked for Cemig for 25 years or more by December 31, 2018. |  |  |  |  |  |  |  |
Description of benefits to participants |  | The program offers payment of the severance amounts specified by law, including payment for notice period, and especial deposit of the 'penalty' amount of 40% of the FGTS (Labour Guarantee Fund) Base Value, and other charges specified by the legislation |  |  |  |  |  |  |  |
Percentage of penalty payment on base value of the employee's FGTS fund |  | 40.00% |  |  |  |  |  |  |  |

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