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Post-Retirement Obligation - Disclosure of Defined Benefit Plans Expense Recognised in Income Statement (Detail) - BRL (R$) R$ in Millions | 12 Months Ended
--- | ---
Dec. 31, 2017 | Dec. 31, 2016 | Dec. 31, 2015
Disclosure of fair value of plan assets [line items] |  |  |
Cost of current service | R$ 19 | R$ 17 | R$ 17
Interest on the actuarial obligation | 1,246 | 1,263 | 1,153
Expected return on the assets of the Plan | (810) | (833) | (933)
Past service cost | (619) |  | (74)
Expense according to actuarial calculation | (164) | 447 | 285
Expense as per actuarial opinion [member] |  |  |
Disclosure of fair value of plan assets [line items] |  |  |
Expense according to actuarial calculation |  |  | 163
Adjustment relating to debt [member] |  |  |
Disclosure of fair value of plan assets [line items] |  |  |
Expense according to actuarial calculation |  |  | 122
Pension plans and retirement supplement plans [member] |  |  |
Disclosure of fair value of plan assets [line items] |  |  |
Cost of current service | 5 | 5 | 6
Interest on the actuarial obligation | 980 | 1,014 | 934
Expected return on the assets of the Plan | (810) | (833) | (933)
Expense according to actuarial calculation | 175 | 186 | 129
Pension plans and retirement supplement plans [member] | Expense as per actuarial opinion [member] |  |  |
Disclosure of fair value of plan assets [line items] |  |  |
Expense according to actuarial calculation |  |  | 7
Pension plans and retirement supplement plans [member] | Adjustment relating to debt [member] |  |  |
Disclosure of fair value of plan assets [line items] |  |  |
Expense according to actuarial calculation |  |  | 122
Health plan [member] |  |  |
Disclosure of fair value of plan assets [line items] |  |  |
Cost of current service | 11 | 9 | 7
Interest on the actuarial obligation | 178 | 173 | 135
Expense according to actuarial calculation | 189 | 182 | 142
Health plan [member] | Expense as per actuarial opinion [member] |  |  |
Disclosure of fair value of plan assets [line items] |  |  |
Expense according to actuarial calculation |  |  | 142
Dental plan [member] |  |  |
Disclosure of fair value of plan assets [line items] |  |  |
Cost of current service |  |  | 1
Interest on the actuarial obligation | 3 | 4 | 3
Expense according to actuarial calculation | 3 | 4 | 4
Dental plan [member] | Expense as per actuarial opinion [member] |  |  |
Disclosure of fair value of plan assets [line items] |  |  |
Expense according to actuarial calculation |  |  | 4
Life insurance [member] |  |  |
Disclosure of fair value of plan assets [line items] |  |  |
Cost of current service | 3 | 3 | 3
Interest on the actuarial obligation | 85 | 72 | 81
Past service cost | (619) |  | (74)
Expense according to actuarial calculation | R$ (531) | R$ 75 | 10
Life insurance [member] | Expense as per actuarial opinion [member] |  |  |
Disclosure of fair value of plan assets [line items] |  |  |
Expense according to actuarial calculation |  |  | R$ 10

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- Definition The increase (decrease) in the net defined benefit liability (asset) resulting from employee service in the current period. [Refer: Net defined benefit liability (asset)] + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Name IAS -Number 19 -IssueDate 2017-01-01 -Paragraph 141 -Subparagraph a -URI http://eifrs.ifrs.org/eifrs/XBRL?type=IAS&num=19&date=2017-03-01&anchor=para_141_a&doctype=Standard -URIDate 2017-03-09 + Details
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- Definition Line items represent concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes of the table. + References No definition available. + Details
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- Definition The increase (decrease) in the net defined benefit liability (asset) resulting from the passage of time. [Refer: Interest expense; Net defined benefit liability (asset)] + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Name IAS -Number 19 -IssueDate 2017-01-01 -Paragraph 141 -Subparagraph b -URI http://eifrs.ifrs.org/eifrs/XBRL?type=IAS&num=19&date=2017-03-01&anchor=para_141_b&doctype=Standard -URIDate 2017-03-09 + Details
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- Definition The increase (decrease) in the net defined benefit liability (asset) resulting from past service cost. Past service cost is the change in the present value of the defined benefit obligation for employee service in prior periods, resulting from a plan amendment (the introduction or withdrawal of, or changes to, a defined benefit plan) or a curtailment (a significant reduction by the entity in the number of employees covered by a plan). [Refer: Net defined benefit liability (asset); Defined benefit plans [member]] + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Name IAS -Number 19 -IssueDate 2017-01-01 -Paragraph 141 -Subparagraph d -URI http://eifrs.ifrs.org/eifrs/XBRL?type=IAS&num=19&date=2017-03-01&anchor=para_141_d&doctype=Standard -URIDate 2017-03-09 + Details
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- Definition Expected return on plan assets net defined benefit liability asset. + References No definition available. + Details
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- Definition Expense net defined benefit liability asset. + References No definition available. + Details
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