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Concession Financial Assets and Liabilities - Summary of Financial Assets and Financial Liabilities With the Tariff Adjustments (Parenthetical) (Detail) | Dec. 31, 2017 BRL (R$)
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CVA account for compensation of changes in portion A costs [member] |
Disclosure Of Financial Assets and Financial Liabilities [line items] |
Excess on energy reserve account | R$ 254

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- Definition Disclosure Of Financial Assets and Financial Liabilities [line items] + References No definition available. + Details
Name: | xcmig_DisclosureOfFinancialAssetsAndFinancialLiabilitiesLineItems
Namespace Prefix: | xcmig_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration

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- Definition Excess on energy reserve account + References No definition available. + Details
Name: | xcmig_ExcessOnEnergyReserveAccount
Namespace Prefix: | xcmig_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | instant

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- Details
Name: | ifrs-full_AssetsAndLiabilitiesAxis=xcmig_CVAAccountForCompensationOfChangesInPortionACostsMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |