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Measurement at Fair Value - Summary of Instruments Measured at Fair Value (Detail) - BRL (R$) R$ in Millions | Dec. 31, 2017 | Dec. 31, 2016
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Disclosure of financial assets and liabilities measured at fair value [Line Items] |  |
Financial assets | R$ 1,053 | R$ 995
Financial liabilities at fair value through profit or loss, category [member] |  |
Disclosure of financial assets and liabilities measured at fair value [Line Items] |  |
Financial liabilities | (857) | (1,342)
Fair value through profit or loss | 566 | (131)
Financial liabilities at fair value through profit or loss, category [member] | Derivative financial instruments [member] |  |
Disclosure of financial assets and liabilities measured at fair value [Line Items] |  |
Financial liabilities | (41) | (1,342)
Financial liabilities at fair value through profit or loss, category [member] | Derivative Financial Instruments Sale Option [member] |  |
Disclosure of financial assets and liabilities measured at fair value [Line Items] |  |
Financial liabilities | (816) |
Financial assets at fair value through profit or loss, classified as held for trading, category [member] | Bank certificates of deposit [member] |  |
Disclosure of financial assets and liabilities measured at fair value [Line Items] |  |
Financial assets |  | 33
Financial assets at fair value through profit or loss, classified as held for trading, category [member] | Treasury financial notes (LFTs) [member] |  |
Disclosure of financial assets and liabilities measured at fair value [Line Items] |  |
Financial assets |  | 193
Financial assets at fair value through profit or loss, classified as held for trading, category [member] | Bank financial notes [Member] |  |
Disclosure of financial assets and liabilities measured at fair value [Line Items] |  |
Financial assets |  | 724
Financial assets at fair value through profit or loss, classified as held for trading, category [member] | Debentures [member] |  |
Disclosure of financial assets and liabilities measured at fair value [Line Items] |  |
Financial assets |  | 45
Financial assets available-for-sale, category [member] |  |
Disclosure of financial assets and liabilities measured at fair value [Line Items] |  |
Financial assets | 370 | 216
Financial assets available-for-sale, category [member] | Infrastructure -Distribution [Member] |  |
Disclosure of financial assets and liabilities measured at fair value [Line Items] |  |
Financial assets | 370 | 216
Financial assets at fair value through profit or loss, category [member] |  |
Disclosure of financial assets and liabilities measured at fair value [Line Items] |  |
Financial assets | 1,044 |
Financial assets at fair value through profit or loss, category [member] | Bank certificates of deposit [member] |  |
Disclosure of financial assets and liabilities measured at fair value [Line Items] |  |
Financial assets | 3 |
Financial assets at fair value through profit or loss, category [member] | Treasury financial notes (LFTs) [member] |  |
Disclosure of financial assets and liabilities measured at fair value [Line Items] |  |
Financial assets | 290 |
Financial assets at fair value through profit or loss, category [member] | Bank financial notes [Member] |  |
Disclosure of financial assets and liabilities measured at fair value [Line Items] |  |
Financial assets | 740 |
Financial assets at fair value through profit or loss, category [member] | Debentures [member] |  |
Disclosure of financial assets and liabilities measured at fair value [Line Items] |  |
Financial assets | 11 |
Financial assets at fair value through profit or loss, category [member] | Derivatives [member] |  |
Disclosure of financial assets and liabilities measured at fair value [Line Items] |  |
Financial assets | 9 |
Level 1 [member] |  |
Disclosure of financial assets and liabilities measured at fair value [Line Items] |  |
Financial assets | 740 | 193
Level 1 [member] | Financial liabilities at fair value through profit or loss, category [member] |  |
Disclosure of financial assets and liabilities measured at fair value [Line Items] |  |
Fair value through profit or loss | 740 | 193
Level 1 [member] | Financial assets at fair value through profit or loss, classified as held for trading, category [member] | Treasury financial notes (LFTs) [member] |  |
Disclosure of financial assets and liabilities measured at fair value [Line Items] |  |
Financial assets |  | 193
Level 1 [member] | Financial assets at fair value through profit or loss, category [member] |  |
Disclosure of financial assets and liabilities measured at fair value [Line Items] |  |
Financial assets | 740 |
Level 1 [member] | Financial assets at fair value through profit or loss, category [member] | Bank financial notes [Member] |  |
Disclosure of financial assets and liabilities measured at fair value [Line Items] |  |
Financial assets | 740 |
Level 2 [member] |  |
Disclosure of financial assets and liabilities measured at fair value [Line Items] |  |
Financial assets | 304 | 802
Level 2 [member] | Financial liabilities at fair value through profit or loss, category [member] |  |
Disclosure of financial assets and liabilities measured at fair value [Line Items] |  |
Financial liabilities | (507) | (1,150)
Fair value through profit or loss | (203) | (348)
Level 2 [member] | Financial liabilities at fair value through profit or loss, category [member] | Derivative financial instruments [member] |  |
Disclosure of financial assets and liabilities measured at fair value [Line Items] |  |
Financial liabilities |  | (1,150)
Level 2 [member] | Financial liabilities at fair value through profit or loss, category [member] | Derivative Financial Instruments Sale Option [member] |  |
Disclosure of financial assets and liabilities measured at fair value [Line Items] |  |
Financial liabilities | (507) |
Level 2 [member] | Financial assets at fair value through profit or loss, classified as held for trading, category [member] | Bank certificates of deposit [member] |  |
Disclosure of financial assets and liabilities measured at fair value [Line Items] |  |
Financial assets |  | 33
Level 2 [member] | Financial assets at fair value through profit or loss, classified as held for trading, category [member] | Bank financial notes [Member] |  |
Disclosure of financial assets and liabilities measured at fair value [Line Items] |  |
Financial assets |  | 724
Level 2 [member] | Financial assets at fair value through profit or loss, classified as held for trading, category [member] | Debentures [member] |  |
Disclosure of financial assets and liabilities measured at fair value [Line Items] |  |
Financial assets |  | 45
Level 2 [member] | Financial assets at fair value through profit or loss, category [member] |  |
Disclosure of financial assets and liabilities measured at fair value [Line Items] |  |
Financial assets | 304 |
Level 2 [member] | Financial assets at fair value through profit or loss, category [member] | Bank certificates of deposit [member] |  |
Disclosure of financial assets and liabilities measured at fair value [Line Items] |  |
Financial assets | 3 |
Level 2 [member] | Financial assets at fair value through profit or loss, category [member] | Treasury financial notes (LFTs) [member] |  |
Disclosure of financial assets and liabilities measured at fair value [Line Items] |  |
Financial assets | 290 |
Level 2 [member] | Financial assets at fair value through profit or loss, category [member] | Debentures [member] |  |
Disclosure of financial assets and liabilities measured at fair value [Line Items] |  |
Financial assets | 11 |
Level 3 [member] |  |
Disclosure of financial assets and liabilities measured at fair value [Line Items] |  |
Financial assets | 9 |
Level 3 [member] | Financial liabilities at fair value through profit or loss, category [member] |  |
Disclosure of financial assets and liabilities measured at fair value [Line Items] |  |
Financial liabilities | (350) | (192)
Fair value through profit or loss | 29 | 24
Level 3 [member] | Financial liabilities at fair value through profit or loss, category [member] | Derivative financial instruments [member] |  |
Disclosure of financial assets and liabilities measured at fair value [Line Items] |  |
Financial liabilities | (41) | (192)
Level 3 [member] | Financial liabilities at fair value through profit or loss, category [member] | Derivative Financial Instruments Sale Option [member] |  |
Disclosure of financial assets and liabilities measured at fair value [Line Items] |  |
Financial liabilities | (309) |
Level 3 [member] | Financial assets available-for-sale, category [member] |  |
Disclosure of financial assets and liabilities measured at fair value [Line Items] |  |
Financial assets | 370 | 216
Level 3 [member] | Financial assets available-for-sale, category [member] | Infrastructure -Distribution [Member] |  |
Disclosure of financial assets and liabilities measured at fair value [Line Items] |  |
Financial assets | 370 | R$ 216
Level 3 [member] | Financial assets at fair value through profit or loss, category [member] | Derivatives [member] |  |
Disclosure of financial assets and liabilities measured at fair value [Line Items] |  |
Financial assets | R$ 9 |

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