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Post-employment Benefits - Summary of Allocation of Assets by Category, Segmented Into Quoted In an Active Market and Not Quoted In an Active Market (Detail) - BRL (R$) R$ in Millions | 12 Months Ended
--- | ---
Dec. 31, 2018 | Dec. 31, 2017 | Dec. 31, 2016
Disclosure of defined benefit plans [line items] |  |  |
Fair Value | R$ 18,808 | R$ 17,588 | R$ 16,520
Percentage of allocation | 100.00% | 100.00% | 100.00%
Fixed income securities [member] |  |  |
Disclosure of defined benefit plans [line items] |  |  |
Fair Value | R$ 18,065 | R$ 16,851 | R$ 15,134
Percentage of allocation | 96.05% | 95.81% | 91.61%
Fixed income securities [member] | Quoted in an active market [member] |  |  |
Disclosure of defined benefit plans [line items] |  |  |
Fair Value | R$ 17,775 | R$ 16,281 | R$ 14,751
Percentage of allocation | 94.51% | 92.57% | 89.29%
Fixed income securities [member] | NonQuoted in an active market [member] |  |  |
Disclosure of defined benefit plans [line items] |  |  |
Fair Value | R$ 290 | R$ 570 | R$ 383
Percentage of allocation | 1.54% | 3.24% | 2.32%
Variable income securities [member] |  |  |
Disclosure of defined benefit plans [line items] |  |  |
Fair Value | R$ 24 | R$ 19 | R$ 685
Percentage of allocation | 0.13% | 0.11% | 4.15%
Variable income securities [member] | Quoted in an active market [member] |  |  |
Disclosure of defined benefit plans [line items] |  |  |
Fair Value | R$ 18 | R$ 15 | R$ 681
Percentage of allocation | 0.09% | 0.09% | 4.12%
Variable income securities [member] | NonQuoted in an active market [member] |  |  |
Disclosure of defined benefit plans [line items] |  |  |
Fair Value | R$ 6 | R$ 4 | R$ 4
Percentage of allocation | 0.04% | 0.02% | 0.03%
Structured investments [member] |  |  |
Disclosure of defined benefit plans [line items] |  |  |
Fair Value | R$ 59 | R$ 24 | R$ 9
Percentage of allocation | 0.31% | 0.14% | 0.05%
Structured investments [member] | Quoted in an active market [member] |  |  |
Disclosure of defined benefit plans [line items] |  |  |
Fair Value | R$ 1 | R$ 1 | R$ 1
Percentage of allocation | 0.01% | 0.01% | 0.01%
Structured investments [member] | NonQuoted in an active market [member] |  |  |
Disclosure of defined benefit plans [line items] |  |  |
Fair Value | R$ 58 | R$ 23 | R$ 8
Percentage of allocation | 0.30% | 0.13% | 0.04%
Real estate [Member] |  |  |
Disclosure of defined benefit plans [line items] |  |  |
Fair Value | R$ 578 | R$ 615 | R$ 623
Percentage of allocation | 3.07% | 3.49% | 3.77%
Loans to participants [Member] |  |  |
Disclosure of defined benefit plans [line items] |  |  |
Fair Value | R$ 82 | R$ 79 | R$ 69
Percentage of allocation | 0.44% | 0.45% | 0.42%

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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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