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Reimbursement Of Tariff Subsidies - Additional Information (Detail) - BRL (R$) R$ in Millions	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Disclosure Of Energy Development Account [Line Items]
Subsidies revenue recognized	R$ 842	R$ 792	R$ 801
Cemig D [member]
Disclosure Of Energy Development Account [Line Items]
Current subsidy receivable	R$ 73	R$ 64

X

- Definition

Current subsidy receivable.

+ References

No definition available.

+ Details

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

X

- Definition

Disclosure of energy development account .

+ References

No definition available.

+ Details

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

X

- Definition

Subsidies revenue recognized.

+ References

No definition available.

+ Details

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

X

- Details

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