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Financial Instruments and Risk Management - Summary of Financial Instruments and Fair Value (Parenthetical) (Detail) R$ in Millions	12 Months Ended
	Dec. 31, 2018 BRL (R$)
Sonda (Cemig Telecom) [member]
Disclosure of detailed information about financial instruments [line items]
Options in shares	R$ 4

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- Definition

Line items represent concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes of the table.

+ References

No definition available.

+ Details

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- Definition

Options in shares amount.

+ References

No definition available.

+ Details

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- Details

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Period Type: