ACQUISITIONS AND DIVESTITURES - Results from Operations from Discontinued Operations (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Jun. 30, 2026	Jun. 30, 2025	Jun. 30, 2026	Jun. 30, 2025
Disposal Group, Including Discontinued Operations [Line Items]
Net income (loss) from discontinued operations	$ (1.0)	$ 24.1	$ (3.0)	$ 60.8
Net income (loss) from discontinued operations attributable to Greif, Inc.	(1.0)	24.1	(3.0)	60.8
Discontinued Operations, Held-for-Sale | Greif Containerboard Solutions, LLC
Disposal Group, Including Discontinued Operations [Line Items]
Net sales	0.0	309.7	0.0	872.0
Cost of products sold	0.0	247.5	0.0	698.2
Gross profit	0.0	62.2	0.0	173.8
Selling, general and administrative expenses	0.0	11.7	0.0	33.4
Loss on disposal of properties, plants and equipment, net	0.0	0.0	0.0	0.2
Loss on disposal of businesses, net	1.4	0.0	4.0	0.0
Operating (loss) profit	(1.4)	50.5	(4.0)	140.2
Interest expense, net	0.0	20.3	0.0	61.7
Income (loss) from discontinued operations before income tax expense and equity earnings of unconsolidated affiliates, net	(1.4)	30.2	(4.0)	78.5
Income tax expense (benefit)	(0.4)	6.1	(1.0)	17.7
Net income (loss) from discontinued operations	(1.0)	24.1	(3.0)	60.8
Net income (loss) from discontinued operations attributable to Greif, Inc.	$ (1.0)	$ 24.1	$ (3.0)	$ 60.8