SUMMARY OF SIGNIFICANT ACCOUNTING PRACTICES (Details)	12 Months Ended
Dec. 31, 2021 shares
Dividends and Interest on equity
Minimum annual mandatory dividend (as a percent)	30.00%
Legal reserve, as a percent of net income	5.00%
Earnings per Share
Antidilutive shares excluded from calculation of diluted EPS	0

Securities (including those issuable pursuant to contingent stock agreements) that could potentially dilute basic earnings per share (EPS) or earnings per unit (EPU) in the future that were not included in the computation of diluted EPS or EPU because to do so would increase EPS or EPU amounts or decrease loss per share or unit amounts for the period presented.

No definition available.

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Namespace Prefix:	ggb_
Data Type:	xbrli:sharesItemType
Balance Type:	na
Period Type:	duration