DIVESTITURES - Results from Operations from Discontinued Operations (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Mar. 31, 2026	Mar. 31, 2025	Mar. 31, 2026	Mar. 31, 2025
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Net income (loss) from discontinued operations	$ 0.0	$ 21.3	$ (2.0)	$ 36.7
Net income (loss) from discontinued operations attributable to Greif, Inc.	0.0	21.3	(2.0)	36.7
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	280.7	0.0	562.3
Cost of products sold	0.0	223.5	0.0	450.7
Gross profit	0.0	57.2	0.0	111.6
Selling, general and administrative expenses	0.0	10.9	0.0	21.7
Loss on disposal of properties, plants and equipment, net	0.0	0.0	0.0	0.2
Loss on disposal of businesses, net	0.0	0.0	2.6	0.0
Operating (loss) profit	0.0	46.3	(2.6)	89.7
Interest expense, net	0.0	19.2	0.0	41.4
Income (loss) from discontinued operations before income tax expense and equity earnings of unconsolidated affiliates, net	0.0	27.1	(2.6)	48.3
Income tax (benefit) expense	0.0	5.8	(0.6)	11.6
Net income (loss) from discontinued operations	0.0	21.3	(2.0)	36.7
Net income (loss) from discontinued operations attributable to Greif, Inc.	$ 0.0	$ 21.3	$ (2.0)	$ 36.7