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Taxes, Amounts to be Restituted to Customers, Income Tax and Social Contribution - Additional Information (Detail) - BRL (R$) R$ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Disclosure of taxes payable [line items]
Taxes on revenues	R$ 8,765	R$ 8,547	R$ 7,702
Cemig D [member]
Disclosure of taxes payable [line items]
Write down tax expense	1,124	1,087
Escrow deposits	1,149	1,110
Taxes on revenues	R$ 25	R$ 23

X

- Definition

Amount in escrow deposits

+ References

No definition available.

+ Details

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Namespace Prefix:	xcmig_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

X

- Definition

Disclosure of taxes payable [line items].

+ References

No definition available.

+ Details

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Namespace Prefix:	xcmig_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

X

- Definition

Taxes on revenues.

+ References

No definition available.

+ Details

Name:	xcmig_TaxesOnRevenues
Namespace Prefix:	xcmig_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

X

- Definition

Wrote-down other income and expenses

+ References

No definition available.

+ Details

Name:	xcmig_WrotedownOtherIncomeAndExpenses
Namespace Prefix:	xcmig_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

X

- Details

Name:	ifrs-full_BorrowingsByNameAxis=xcmig_CemigDMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type: