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Insurance - Summary of Amounts Arising From Insurance Contracts (Detail) - 12 months ended Dec. 31, 2017 R$ in Thousands, $ in Thousands	BRL (R$)	USD ($)	USD ($)
Companhia Energetica de Minas Gerais Holding [Member] | Facilities in buildings [member]
Disclosure of types of insurance contracts [line items]
Cover	Fire	Fire
Amount insured	R$ 53,348
Annual premium	R$ 12
Companhia Energetica de Minas Gerais Holding [Member] | Bottom of range [member] | Facilities in buildings [member]
Disclosure of types of insurance contracts [line items]
Dates of cover	Jan 8, 2018	Jan 8, 2018
Companhia Energetica de Minas Gerais Holding [Member] | Top of range [member] | Facilities in buildings [member]
Disclosure of types of insurance contracts [line items]
Dates of cover	Jan 8, 2019	Jan 8, 2019
Cemig Geracao e Transmissao [member] | Air transport Aircraft Fuselage [member]
Disclosure of types of insurance contracts [line items]
Cover	Fuselage	Fuselage
Amount insured | $			$ 4,675
Cemig Geracao e Transmissao [member] | Air transport [member]
Disclosure of types of insurance contracts [line items]
Cover	Third party	Third party
Amount insured | $			14,000
Annual premium | $		$ 58
Cemig Geracao e Transmissao [member] | Ware house stores [member]
Disclosure of types of insurance contracts [line items]
Cover	Fire	Fire
Amount insured	R$ 14,931
Annual premium	R$ 21
Cemig Geracao e Transmissao [member] | Buildings [member]
Disclosure of types of insurance contracts [line items]
Cover	Fire	Fire
Amount insured	R$ 454,828
Annual premium	R$ 98
Cemig Geracao e Transmissao [member] | Telecoms equipment [member]
Disclosure of types of insurance contracts [line items]
Cover	Fire	Fire
Amount insured	R$ 11,514
Annual premium	R$ 5
Cemig Geracao e Transmissao [member] | Operational risk [member]
Disclosure of types of insurance contracts [line items]
Cover	-	-
Amount insured	R$ 1,333,711
Annual premium	R$ 1,790
Cemig Geracao e Transmissao [member] | Bottom of range [member] | Air transport [member]
Disclosure of types of insurance contracts [line items]
Dates of cover	Apr 29, 2017	Apr 29, 2017
Cemig Geracao e Transmissao [member] | Bottom of range [member] | Ware house stores [member]
Disclosure of types of insurance contracts [line items]
Dates of cover	Oct 02, 2017	Oct 02, 2017
Cemig Geracao e Transmissao [member] | Bottom of range [member] | Buildings [member]
Disclosure of types of insurance contracts [line items]
Dates of cover	Jan 08, 2018	Jan 08, 2018
Cemig Geracao e Transmissao [member] | Bottom of range [member] | Telecoms equipment [member]
Disclosure of types of insurance contracts [line items]
Dates of cover	Jan 08, 2018	Jan 08, 2018
Cemig Geracao e Transmissao [member] | Bottom of range [member] | Operational risk [member]
Disclosure of types of insurance contracts [line items]
Dates of cover	Dec 07, 2017	Dec 07, 2017
Cemig Geracao e Transmissao [member] | Top of range [member] | Air transport [member]
Disclosure of types of insurance contracts [line items]
Dates of cover	Apr 29, 2018	Apr 29, 2018
Cemig Geracao e Transmissao [member] | Top of range [member] | Ware house stores [member]
Disclosure of types of insurance contracts [line items]
Dates of cover	Oct 02, 2018	Oct 02, 2018
Cemig Geracao e Transmissao [member] | Top of range [member] | Buildings [member]
Disclosure of types of insurance contracts [line items]
Dates of cover	Jan 08, 2019	Jan 08, 2019
Cemig Geracao e Transmissao [member] | Top of range [member] | Telecoms equipment [member]
Disclosure of types of insurance contracts [line items]
Dates of cover	Jan 08, 2019	Jan 08, 2019
Cemig Geracao e Transmissao [member] | Top of range [member] | Operational risk [member]
Disclosure of types of insurance contracts [line items]
Dates of cover	Dec 07, 2018	Dec 07, 2018
Cemig Distribution [member] | Facilities in buildings [member]
Disclosure of types of insurance contracts [line items]
Cover	Fire	Fire
Amount insured	R$ 1,003,221
Annual premium	R$ 217
Cemig Distribution [member] | Air transport Aircraft Fuselage [member]
Disclosure of types of insurance contracts [line items]
Cover	Fuselage	Fuselage
Amount insured | $			3,613
Cemig Distribution [member] | Air transport [member]
Disclosure of types of insurance contracts [line items]
Cover	Third party	Third party
Amount insured | $			$ 14,000
Annual premium	R$ 42	$ 42
Cemig Distribution [member] | Ware house stores [member]
Disclosure of types of insurance contracts [line items]
Cover	Fire	Fire
Amount insured	R$ 84,169
Annual premium	R$ 120
Cemig Distribution [member] | Telecoms equipment [member]
Disclosure of types of insurance contracts [line items]
Cover	Fire	Fire
Amount insured	R$ 17,208
Annual premium	R$ 7
Cemig Distribution [member] | Operational risk [member]
Disclosure of types of insurance contracts [line items]
Cover	Total	Total
Amount insured	R$ 471,265
Annual premium	R$ 633
Cemig Distribution [member] | Bottom of range [member] | Facilities in buildings [member]
Disclosure of types of insurance contracts [line items]
Dates of cover	Jan 08, 2018	Jan 08, 2018
Cemig Distribution [member] | Bottom of range [member] | Air transport [member]
Disclosure of types of insurance contracts [line items]
Dates of cover	Apr 29, 2017	Apr 29, 2017
Cemig Distribution [member] | Bottom of range [member] | Ware house stores [member]
Disclosure of types of insurance contracts [line items]
Dates of cover	Oct 02, 2017	Oct 02, 2017
Cemig Distribution [member] | Bottom of range [member] | Telecoms equipment [member]
Disclosure of types of insurance contracts [line items]
Dates of cover	Jan 08, 2018	Jan 08, 2018
Cemig Distribution [member] | Bottom of range [member] | Operational risk [member]
Disclosure of types of insurance contracts [line items]
Dates of cover	Dec 07, 2017	Dec 07, 2017
Cemig Distribution [member] | Top of range [member] | Facilities in buildings [member]
Disclosure of types of insurance contracts [line items]
Dates of cover	Jan 08, 2019	Jan 08, 2019
Cemig Distribution [member] | Top of range [member] | Air transport [member]
Disclosure of types of insurance contracts [line items]
Dates of cover	Apr 29, 2018	Apr 29, 2018
Cemig Distribution [member] | Top of range [member] | Ware house stores [member]
Disclosure of types of insurance contracts [line items]
Dates of cover	Oct 02, 2018	Oct 02, 2018
Cemig Distribution [member] | Top of range [member] | Telecoms equipment [member]
Disclosure of types of insurance contracts [line items]
Dates of cover	Jan 08, 2019	Jan 08, 2019
Cemig Distribution [member] | Top of range [member] | Operational risk [member]
Disclosure of types of insurance contracts [line items]
Dates of cover	Dec 07, 2018	Dec 07, 2018
Gasmig [member] | Gas Distribution Network Third Party [Member]
Disclosure of types of insurance contracts [line items]
Cover	Third party	Third party
Amount insured	R$ 60,000
Annual premium	R$ 429
Gasmig [member] | Own Vehicle Fleet Operation [Member]
Disclosure of types of insurance contracts [line items]
Cover	Damage to third parties only	Damage to third parties only
Amount insured	R$ 500
Annual premium	R$ 2
Gasmig [member] | Own Vehicle Fleet Directors [Member]
Disclosure of types of insurance contracts [line items]
Cover	Full cover	Full cover
Amount insured	R$ 100
Annual premium	R$ 1
Gasmig [member] | Facilities Multirisk [Member]
Disclosure of types of insurance contracts [line items]
Cover	Robbery, theft and fire	Robbery, theft and fire
Amount insured	R$ 41,374
Gasmig [member] | Bottom of range [member] | Gas Distribution Network Third Party [Member]
Disclosure of types of insurance contracts [line items]
Dates of cover	Dec 15, 2017	Dec 15, 2017
Gasmig [member] | Bottom of range [member] | Own Vehicle Fleet Operation [Member]
Disclosure of types of insurance contracts [line items]
Dates of cover	Jul 07, 2017	Jul 07, 2017
Gasmig [member] | Bottom of range [member] | Own Vehicle Fleet Directors [Member]
Disclosure of types of insurance contracts [line items]
Dates of cover	Oct 25, 2017	Oct 25, 2017
Gasmig [member] | Bottom of range [member] | Facilities Multirisk [Member]
Disclosure of types of insurance contracts [line items]
Dates of cover	Jan 01, 2017	Jan 01, 2017
Gasmig [member] | Top of range [member] | Gas Distribution Network Third Party [Member]
Disclosure of types of insurance contracts [line items]
Dates of cover	Dec 15, 2018	Dec 15, 2018
Gasmig [member] | Top of range [member] | Own Vehicle Fleet Operation [Member]
Disclosure of types of insurance contracts [line items]
Dates of cover	Jul 07, 2018	Jul 07, 2018
Gasmig [member] | Top of range [member] | Own Vehicle Fleet Directors [Member]
Disclosure of types of insurance contracts [line items]
Dates of cover	Oct 25, 2018	Oct 25, 2018
Gasmig [member] | Top of range [member] | Facilities Multirisk [Member]
Disclosure of types of insurance contracts [line items]
Dates of cover	Jan 01, 2018	Jan 01, 2018

X

- Definition

The amount of assets under insurance contracts and reinsurance contracts issued. [Refer: Types of insurance contracts [member]]

+ References

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+ Details

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Balance Type:	debit
Period Type:	instant

X

- Definition

Line items represent concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes of the table.

+ References

No definition available.

+ Details

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Namespace Prefix:	ifrs-full_
Data Type:	xbrli:stringItemType
Balance Type:	na
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X

- Definition

The amount of premiums written, net of amounts reinsured with third parties.

+ References

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Name IAS
-Number 1
-IssueDate 2017-01-01
-Paragraph 85
-URI http://eifrs.ifrs.org/eifrs/XBRL?type=IAS&num=1&date=2017-03-01&anchor=para_85&doctype=Standard
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+ Details

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Namespace Prefix:	ifrs-full_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

X

- Definition

Insurance coverage period one.

+ References

No definition available.

+ Details

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

X

- Definition

Type of insurance coverage.

+ References

No definition available.

+ Details

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

X

- Details

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Namespace Prefix:
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Balance Type:
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- Details

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Namespace Prefix:
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Balance Type:
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- Details

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Namespace Prefix:
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- Details

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Namespace Prefix:
Data Type:	na
Balance Type:
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- Details

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Namespace Prefix:
Data Type:	na
Balance Type:
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X

- Details

Name:	ifrs-full_TypesOfInsuranceContractsAxis=xcmig_AirTransportAircraftThirdPartyLiabilityMember
Namespace Prefix:
Data Type:	na
Balance Type:
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- Details

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Balance Type:
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- Details

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Namespace Prefix:
Data Type:	na
Balance Type:
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- Details

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Balance Type:
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