Insurance - Summary of Amounts Arising From Insurance Contracts (Parenthetical) (Detail) - 12 months ended Dec. 31, 2018 R$ in Millions, $ in Millions	BRL (R$)	USD ($)
Disclosure of types of insurance contracts [line items]
Expense arising from insurance	R$ 0	$ 0
Cemig Geracao e Transmissao [member]
Disclosure of types of insurance contracts [line items]
Maximum indemnity limit	R$ 231

The amount of expense arising from insurance contracts. [Refer: Types of insurance contracts [member]]

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Note Expiry date 2021-01-01
-Name IFRS
-Number 4
-IssueDate 2018-01-01
-Paragraph 37
-Subparagraph b
-URI http://eifrs.ifrs.org/eifrs/XBRL?type=IFRS&num=4&date=2018-03-02&anchor=para_37_b&doctype=Standard&book=b
-URIDate 2018-03-16

Name:	ifrs-full_ExpenseArisingFromInsuranceContracts
Namespace Prefix:	ifrs-full_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration