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Post-Retirement Obligation - Summary of Fair Value of Pension Plan Assets Issued by Sponsor and Subsidiaries (Detail) - BRL (R$) R$ in Millions | Dec. 31, 2017 | Dec. 31, 2016
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Disclosure of fair value of plan assets [line items] |  |
Assets of the pension plan | R$ 1,098 | R$ 1,114
Non-convertible debentures issued by the Company and subsidiaries [member] |  |
Disclosure of fair value of plan assets [line items] |  |
Assets of the pension plan | 363 | 397
Shares issued by the Company [member] |  |
Disclosure of fair value of plan assets [line items] |  |
Assets of the pension plan | 10 | 7
Real estate properties of the Foundation, occupied by the Company and subsidiaries [member] |  |
Disclosure of fair value of plan assets [line items] |  |
Assets of the pension plan | R$ 725 | R$ 710

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- Definition The amount that securities that are backed by underlying assets constitute of the fair value of defined benefit plan assets. [Refer: Plan assets, at fair value; Defined benefit plans [member]] + References Reference 1: http://www.xbrl.org/2003/role/exampleRef -Name IAS -Number 19 -IssueDate 2017-01-01 -Paragraph 142 -Subparagraph g -URI http://eifrs.ifrs.org/eifrs/XBRL?type=IAS&num=19&date=2017-03-01&anchor=para_142_g&doctype=Standard -URIDate 2017-03-09 + Details
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