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Revenues - Additional Information (Detail) - BRL (R$) R$ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Revenue [abstract]
Transmission concession revenue	R$ 13
Transmission indemnity revenue	250	R$ 373	R$ 751
Generation indemnity revenue	R$ 55	R$ 271

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- References

No definition available.

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Name:	ifrs-full_RevenueAbstract
Namespace Prefix:	ifrs-full_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

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- Definition

Revenue From Generation Indemnity

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No definition available.

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Name:	xcmig_RevenueFromGenerationIndemnity
Namespace Prefix:	xcmig_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

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- Definition

Revenue from transmission indemnity.

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No definition available.

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Name:	xcmig_RevenueFromTransmissionIndemnity
Namespace Prefix:	xcmig_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

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- Definition

Transmission concession revenue.

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No definition available.

+ Details

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