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Concessions and Authorizations - Schedule of Present Value and Nominal Value Portion to be paid (Detail) R$ in Millions | 12 Months Ended
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Dec. 31, 2017 BRL (R$)
Irape enterprise [member] |
Disclosure Of Present Value And Nominal Value Portion To Be Paid [Line Items] |
Percentage interest | 100.00%
Amounts paid in 2017 | R$ 2
Present value of amounts to be paid in 12 months | 2
Nominal value of amounts to be paid in 12 months | R$ 2
Queimadao Consortium Enterprise [member] |
Disclosure Of Present Value And Nominal Value Portion To Be Paid [Line Items] |
Percentage interest | 82.50%
Amounts paid in 2017 | R$ 1
Present value of amounts to be paid in 12 months | 1
Nominal value of amounts to be paid in 12 months | R$ 1
Salto Morais, Rio de Pedras and Others [member] |
Disclosure Of Present Value And Nominal Value Portion To Be Paid [Line Items] |
Percentage interest | 100.00%
Amounts paid in 2017 | R$ 1
Present value of amounts to be paid in 12 months | 1
Nominal value of amounts to be paid in 12 months | R$ 1

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- Definition Concession amount paid. + References No definition available. + Details
Name: | xcmig_ConcessionAmountPaid
Namespace Prefix: | xcmig_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration

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- Definition Disclosure of present value and nominal value portion to be paid line items. + References No definition available. + Details
Name: | xcmig_DisclosureOfPresentValueAndNominalValuePortionToBePaidLineItems
Namespace Prefix: | xcmig_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration

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- Definition Nominal value of amounts to be paid in next twelve months. + References No definition available. + Details
Name: | xcmig_NominalValueOfAmountsToBePaidInNextTwelveMonths
Namespace Prefix: | xcmig_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | instant

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- Definition Percentage of concession interest. + References No definition available. + Details
Name: | xcmig_PercentageOfConcessionInterest
Namespace Prefix: | xcmig_
Data Type: | num:percentItemType
Balance Type: | na
Period Type: | duration

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- Definition Present value of concession amounts to be paid in next twelve months. + References No definition available. + Details
Name: | xcmig_PresentValueOfConcessionAmountsToBePaidInNextTwelveMonths
Namespace Prefix: | xcmig_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | instant

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- Details
Name: | ifrs-full_ClassesOfPropertyPlantAndEquipmentAxis=xcmig_IrapeEnterpriseMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

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- Details
Name: | ifrs-full_ClassesOfPropertyPlantAndEquipmentAxis=xcmig_QueimadaoConsortiumEnterpriseMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

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- Details
Name: | ifrs-full_ClassesOfPropertyPlantAndEquipmentAxis=xcmig_SaltoMoraisRioDePedrasAndOthersEnterpriseMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |