Post-Retirement Obligation - Summary of Expectation for Payment of Benefits (Detail) R$ in Millions	12 Months Ended
Dec. 31, 2017 BRL (R$)
Disclosure of defined benefit plans [line items]
Estimate of payment of benefits	R$ 1,003
Pension plans and retirement supplement plans [member]
Disclosure of defined benefit plans [line items]
Estimate of payment of benefits	875
Health plan [member]
Disclosure of defined benefit plans [line items]
Estimate of payment of benefits	117
Dental plan [member]
Disclosure of defined benefit plans [line items]
Estimate of payment of benefits	3
Life insurance [member]
Disclosure of defined benefit plans [line items]
Estimate of payment of benefits	R$ 8

The estimate of the expected contributions to be made to a defined benefit plan for the next annual reporting period. [Refer: Defined benefit plans [member]]

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Name IAS
-Number 19
-IssueDate 2017-01-01
-Paragraph 147
-Subparagraph b
-URI http://eifrs.ifrs.org/eifrs/XBRL?type=IAS&num=19&date=2017-03-01&anchor=para_147_b&doctype=Standard
-URIDate 2017-03-09

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Name IAS
-Number 19
-IssueDate 2017-01-01
-Paragraph 148
-Subparagraph d
-Clause iii
-URI http://eifrs.ifrs.org/eifrs/XBRL?type=IAS&num=19&date=2017-03-01&anchor=para_148_d_iii&doctype=Standard
-URIDate 2017-03-09

Name:	ifrs-full_EstimateOfContributionsExpectedToBePaidToPlan
Namespace Prefix:	ifrs-full_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration