Shareholders' equity - Summary of Calculation of Dividends and Interest on Capital (Detail) - BRL (R$) R$ in Millions	12 Months Ended
Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Disclosure of Dividends [abstract]
Statutory net income	R$ 26,712	R$ 21,945	R$ 21,108
Legal reserve	(1,336)	(1,097)	(1,055)
Dividend calculation basis	25,376	20,848	20,053
Mandatory dividend	6,344	5,212	5,013
Dividends and Interest on Capital Paid / Accrued / Identified	R$ 18,777	R$ 22,437	R$ 17,558

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 2019-01-01
-Paragraph 55
-URI http://eifrs.ifrs.org/eifrs/xifrs-link?type=IAS&num=1&code=ifrs-tx-2019-en-r&anchor=para_55&doctype=Standard
-URIDate 2019-03-27

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