20. INTANGIBLE ASSETS (Details Narrative) - BRL (R$) R$ in Millions	12 Months Ended
Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Disclosure of detailed information about intangible assets [abstract]
Capitalized borrowing costs	R$ 2	R$ 4	R$ 71
Annual average amortization rate	4.01%

Amount refers to useful lives or amortisation rates intangible assets other than goodwill.

No definition available.

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