Shareholders' equity - Summary of Calculation of Dividends and Interest on Capital (Detail) - BRL (R$) R$ in Millions	12 Months Ended
Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Disclosure of Dividends [abstract]
Statutory net income	R$ 21,945	R$ 21,108	R$ 18,853
Legal reserve	(1,097)	(1,055)	(943)
Dividend calculation basis	20,848	20,053	17,910
Mandatory dividend	5,212	5,013	4,478
Dividends and Interest on Capital Paid / Provided for / Identified	R$ 22,437	R$ 17,558	R$ 10,000

A component of equity representing reserves created based on legal requirements.

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Name IAS
-Number 1
-IssueDate 2017-01-01
-Paragraph 55
-URI http://eifrs.ifrs.org/eifrs/XBRL?type=IAS&num=1&date=2017-03-01&anchor=para_55&doctype=Standard
-URIDate 2017-03-09

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Namespace Prefix:	ifrs-full_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant