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Post-Retirement Obligation - Disclosure Of Consolidated Actuarial Information (Detail) - BRL (R$) R$ in Millions | Dec. 31, 2017 | Dec. 31, 2016 | Dec. 31, 2015 | Dec. 31, 2014
--- | --- | --- | --- | ---
Disclosure of defined benefit plans [line items] |  |  |  |
Net liabilities in the statement of financial position | R$ 4,186 | R$ 4,242 | R$ 3,253 | R$ 2,631
Pension plans and retirement supplement plans [member] |  |  |  |
Disclosure of defined benefit plans [line items] |  |  |  |
Fair value of plan assets | (8,546) | (8,128) | (6,703) | (8,051)
Health plan [member] |  |  |  |
Disclosure of defined benefit plans [line items] |  |  |  |
Net liabilities in the statement of financial position | 1,809 | 1,711 | 1,323 | 1,120
Dental plan [member] |  |  |  |
Disclosure of defined benefit plans [line items] |  |  |  |
Net liabilities in the statement of financial position | 38 | 38 | R$ 30 | R$ 33
Actuarial assumptions [Member] |  |  |  |
Disclosure of defined benefit plans [line items] |  |  |  |
Present value of funded obligations | 12,663 | 12,306 |  |
Fair value of plan assets | (8,546) | (8,128) |  |
Net liabilities in the statement of financial position | 4,186 | 4,242 |  |
Actuarial assumptions [Member] | Initial net liabilities [member] |  |  |  |
Disclosure of defined benefit plans [line items] |  |  |  |
Net liabilities in the statement of financial position | 4,117 | 4,178 |  |
Actuarial assumptions [Member] | Adjustment to asset ceiling [member] |  |  |  |
Disclosure of defined benefit plans [line items] |  |  |  |
Net liabilities in the statement of financial position | 69 | 64 |  |
Actuarial assumptions [Member] | Pension plans and retirement supplement plans [member] |  |  |  |
Disclosure of defined benefit plans [line items] |  |  |  |
Present value of funded obligations | 10,545 | 9,743 |  |
Fair value of plan assets | (8,546) | (8,128) |  |
Net liabilities in the statement of financial position | 2,068 | 1,679 |  |
Actuarial assumptions [Member] | Pension plans and retirement supplement plans [member] | Initial net liabilities [member] |  |  |  |
Disclosure of defined benefit plans [line items] |  |  |  |
Net liabilities in the statement of financial position | 1,999 | 1,615 |  |
Actuarial assumptions [Member] | Pension plans and retirement supplement plans [member] | Adjustment to asset ceiling [member] |  |  |  |
Disclosure of defined benefit plans [line items] |  |  |  |
Net liabilities in the statement of financial position | 69 | 64 |  |
Actuarial assumptions [Member] | Health plan [member] |  |  |  |
Disclosure of defined benefit plans [line items] |  |  |  |
Present value of funded obligations | 1,809 | 1,711 |  |
Net liabilities in the statement of financial position | 1,809 | 1,711 |  |
Actuarial assumptions [Member] | Health plan [member] | Initial net liabilities [member] |  |  |  |
Disclosure of defined benefit plans [line items] |  |  |  |
Net liabilities in the statement of financial position | 1,809 | 1,711 |  |
Actuarial assumptions [Member] | Dental plan [member] |  |  |  |
Disclosure of defined benefit plans [line items] |  |  |  |
Present value of funded obligations | 39 | 38 |  |
Net liabilities in the statement of financial position | 39 | 38 |  |
Actuarial assumptions [Member] | Dental plan [member] | Initial net liabilities [member] |  |  |  |
Disclosure of defined benefit plans [line items] |  |  |  |
Net liabilities in the statement of financial position | 39 | 38 |  |
Actuarial assumptions [Member] | Life insurance [member] |  |  |  |
Disclosure of defined benefit plans [line items] |  |  |  |
Present value of funded obligations | 270 | 814 |  |
Net liabilities in the statement of financial position | 270 | 814 |  |
Actuarial assumptions [Member] | Life insurance [member] | Initial net liabilities [member] |  |  |  |
Disclosure of defined benefit plans [line items] |  |  |  |
Net liabilities in the statement of financial position | R$ 270 | R$ 814 |  |

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- Definition The present value, without deducting any plan assets, of expected future payments required to settle the obligation resulting from employee service in the current and prior periods. [Refer: Plan assets, at fair value] + References Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef -Name IAS -Number 19 -IssueDate 2017-01-01 -Paragraph 57 -Subparagraph a -URI http://eifrs.ifrs.org/eifrs/XBRL?type=IAS&num=19&date=2017-03-01&anchor=para_57_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 fair value of defined benefit plan assets. Plan assets comprise assets held by a long-term employee benefit fund and qualifying insurance policies. [Refer: At fair value [member]] + References Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef -Name IAS -Number 19 -IssueDate 2017-01-01 -Paragraph 57 -Subparagraph a -URI http://eifrs.ifrs.org/eifrs/XBRL?type=IAS&num=19&date=2017-03-01&anchor=para_57_a&doctype=Standard -URIDate 2017-03-09 + Details
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- Definition The present value of the defined benefit obligation, less the fair value of the plan assets (if any). [Refer: Plan assets [member]] + References Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef -Name IAS -Number 19 -IssueDate 2017-01-01 -Paragraph 57 -Subparagraph a -URI http://eifrs.ifrs.org/eifrs/XBRL?type=IAS&num=19&date=2017-03-01&anchor=para_57_a&doctype=Standard -URIDate 2017-03-09 + Details
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