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Revenues - Additional Information (Detail) - BRL (R$) R$ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Revenue [abstract]
Transmission indemnity revenue	R$ 373	R$ 751	R$ 101
Revenue from indemnity by IPCA	224
Adjustment of BRR of transmission assets	149
Generation indemnity revenue	R$ 271

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Adjustment of BRR of Transmission Assets

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Revenue From Generation Indemnity

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Revenue from indemnity receivable by extended consumer price index.

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Revenue from transmission indemnity.

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