DIVESTITURES - Results from Operations from Discontinued Operations (Details) - USD ($) $ in Millions	3 Months Ended
	Dec. 31, 2025	Dec. 31, 2024
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Net (loss) income from discontinued operations	$ (2.0)	$ 15.4
Net (loss) income from discontinued operations attributable to Greif, Inc.	(2.0)	15.4
Discontinued Operations, Held-for-Sale | Greif Containerboard Solutions, LLC
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Net sales	0.0	281.6
Cost of products sold	0.0	227.2
Gross profit	0.0	54.4
Selling, general and administrative expenses	0.0	10.8
Loss on disposal of properties, plants and equipment, net	0.0	0.2
Loss on disposal of businesses, net	2.6	0.0
Operating (loss) profit	(2.6)	43.4
Interest expense, net	0.0	22.2
(Loss) income from discontinued operations before income tax expense and equity earnings of unconsolidated affiliates, net	(2.6)	21.2
Income tax (benefit) expense	(0.6)	5.8
Net (loss) income from discontinued operations	(2.0)	15.4
Net (loss) income from discontinued operations attributable to Greif, Inc.	$ (2.0)	$ 15.4