DERIVATIVES - Commodity Contract Commitments (Details)	12 Months Ended
	Aug. 31, 2020 MWh t
Aluminum | Long
Derivative [Line Items]
Commodity contract commitments	1,675
Copper | Long
Derivative [Line Items]
Commodity contract commitments	556
Copper | Short
Derivative [Line Items]
Commodity contract commitments	8,346
Electricity | Long
Derivative [Line Items]
Energy contract commitments | MWh	2,000,000