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Cover - shares
 12 Months Ended
Dec. 31, 2021
Dec. 31, 2020
Entity Addresses [Line Items]    
Document Type 20-F  
Amendment Flag false  
Document Registration Statement false  
Document Annual Report true  
Document Transition Report false  
Document Shell Company Report false  
Document Period End Date Dec. 31, 2021  
Document Fiscal Period Focus FY  
Document Fiscal Year Focus 2021  
Current Fiscal Year End Date --12-31  
Entity File Number 1-15224  
Entity Registrant Name ENERGY CO OF MINAS GERAIS  
Entity Central Index Key 0001157557  
Entity Incorporation, State or Country Code D5  
Entity Address, Address Line One 1200, Avenida Barbacena  
Entity Address, City or Town Belo Horizonte/MG  
Entity Address, Country BR  
Entity Address, Postal Zip Code CEP 30190-131  
Title of 12(b) Security Preferred Shares, R$5.00 par value  
Trading Symbol CIG  
Security Exchange Name NYSE  
Entity Well-known Seasoned Issuer Yes  
Entity Voluntary Filers No  
Entity Current Reporting Status Yes  
Entity Interactive Data Current Yes  
Entity Filer Category Large Accelerated Filer  
Entity Emerging Growth Company false  
Document Accounting Standard International Financial Reporting Standards  
Entity Shell Company false  
ICFR Auditor Attestation Flag true  
Auditor Firm ID 1448 1351
Auditor Name Ernst & Young Auditores Independentes S.S.  
Auditor Location Belo Horizonte  
Common Shares [Member]    
Entity Addresses [Line Items]    
Entity Common Stock, Shares Outstanding 735,847,624  
Preferred Shares [Member]    
Entity Addresses [Line Items]    
Entity Common Stock, Shares Outstanding 1,465,523,064  
Business Contact [Member]    
Entity Addresses [Line Items]    
Entity Address, Address Line One 1200, Avenida Barbacena  
Entity Address, City or Town Belo Horizonte/MG  
Entity Address, Country BR  
Entity Address, Postal Zip Code 30190-131  
City Area Code 55  
Local Phone Number 3506-5024  
Contact Personnel Name Leonardo George de Magalhães  
Contact Personnel Email Address ri@cemig.com.br