CHANGES IN BUSINESS (Details) $ in Millions		12 Months Ended
	Nov. 05, 2018 USD ($) fabrication_facility mini_mill	Aug. 31, 2021 USD ($) location mini_mill	Aug. 31, 2020 USD ($)
Business Combinations [Abstract]
Number of rebar fabrication facilities acquired | fabrication_facility	33
Number of electric arc furnace mini mills | mini_mill	4	7
Cash purchase price	$ 701.2
Net sales of acquired business		$ 1,400.0
Net earnings of acquired business		132.7
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Facility closure costs		$ 13.8	$ 9.8
Number of facilities idled | location		6
Severance costs			6.2
Working capital adjustment			$ 32.1
Assets Held-for-sale, Not Part of Disposal Group		$ 24.9
Proceeds from sale of assets associated with facilities		$ 300.0