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SHORT-TERM DEBT AND LONG-TERM DEBT - Additional disclosures (Details) R$ in Thousands, $ in Millions	Dec. 31, 2020 USD ($)	Dec. 31, 2020 BRL (R$)	Dec. 31, 2019 BRL (R$)	Oct. 31, 2019 BRL (R$)
LOANS AND FINANCING
Loans and financing		R$ 14,612,934	R$ 13,138,823
Working capital
LOANS AND FINANCING
Loans and financing		1,178,557	R$ 107,312
Global Credit Line
LOANS AND FINANCING
Amount of outstanding balance credit facility	$ 40	207,000
Maximum borrowing capacity		4,157,000		R$ 800,000
Bonds | Gerdau Acos Longos and Gerdau Acominas
LOANS AND FINANCING
Principal amount | $	$ 300
Amount outstanding		R$ 1,175

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Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Name IAS
-Number 1
-IssueDate 2020-01-01
-Paragraph 55
-URI http://eifrs.ifrs.org/eifrs/xifrs-link?type=IAS&num=1&code=ifrs-tx-2020-en-r&anchor=para_55&doctype=Standard
-URIDate 2020-01-01

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