Equity and Remuneration to Shareholders - Summary of Calculation of Diluted Earnings per Share (Detail) - BRL (R$) R$ / shares in Units, shares in Millions, R$ in Millions	12 Months Ended
Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Earnings per share [line items]
Net income for the year	R$ 1,002	R$ 334	R$ 2,469
Preferred shares [member]
Earnings per share [line items]
Total basic earnings for the preferred shares	819	291	1,643
Diluted earnings for the common shares (D)	R$ 819	R$ 264	R$ 1,643
Diluted earnings per common share ( D / No. of common shares )	R$ 0.84	R$ 0.32	R$ 1.96
Common shares [member]
Earnings per share [line items]
Total basic earnings for the preferred shares	R$ 182	R$ 44	R$ 826
Diluted earnings for the common shares (D)	R$ 182	R$ 30	R$ 826
Diluted earnings per common share ( D / No. of common shares )	R$ 0.37	R$ 0.07	R$ 1.96
RME/Lepsa Option [Member] \| Preferred shares [member]
Earnings per share [line items]
Dilutive effect		(22)
RME/Lepsa Option [Member] \| Common shares [member]
Earnings per share [line items]
Dilutive effect		(11)
Ativas Option [Member] \| Preferred shares [member]
Earnings per share [line items]
Dilutive effect		(5)
Ativas Option [Member] \| Common shares [member]
Earnings per share [line items]
Dilutive effect		(2)

The amount of profit (loss) attributable to ordinary equity holders of the parent entity (the numerator), divided by the weighted average number of ordinary shares outstanding during the period (the denominator), both adjusted for the effects of all dilutive potential ordinary shares. [Refer: Ordinary shares [member]; Weighted average [member]]

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The number of dilutive potential ordinary shares that relate to the assumed exercise of the entity's share options.

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