Earnings Per Share - Computation of Earnings Per Share Basic and Diluted (Details) - USD ($) $ / shares in Units, $ in Millions	3 Months Ended								12 Months Ended
	Oct. 31, 2020	Jul. 31, 2020	Apr. 30, 2020	Jan. 31, 2020	Oct. 31, 2019	Jul. 31, 2019	Apr. 30, 2019	Jan. 31, 2019	Oct. 31, 2020	Oct. 31, 2019	Oct. 31, 2018
Numerator for basic and diluted EPS
Net income attributable to Greif	$ 44.4	$ 20.7	$ 11.4	$ 32.3	$ 65.0	$ 62.7	$ 13.6	$ 29.7	$ 108.8	$ 171.0	$ 209.4
Cash dividends									(104.3)	(104.0)	(100.0)
Undistributed net income (loss) attributable to Greif, Inc.									$ 4.5	$ 67.0	$ 109.4
Class A common stock
Denominator for basic EPS
Denominator for basic EPS (shares)	26,441,986	26,441,986	26,386,439	26,260,943	26,257,943	26,257,943	26,250,460	25,991,433	26,382,838	26,189,445	25,915,887
Denominator for diluted EPS
Denominator for diluted EPS (shares)	26,512,331	26,442,595	26,386,439	26,414,280	26,360,148	26,257,943	26,255,112	25,991,433	26,390,643	26,215,111	25,965,856
Basic:
EPS Basic (usd per share)	$ 0.74	$ 0.35	$ 0.19	$ 0.55	$ 1.09	$ 1.06	$ 0.23	$ 0.51	$ 1.83	$ 2.89	$ 3.56
EPS Diluted
EPS Diluted (usd per share)	$ 0.74	$ 0.35	$ 0.19	$ 0.55	$ 1.09	$ 1.06	$ 0.23	$ 0.51	$ 1.83	$ 2.89	$ 3.55
Class B common stock
Denominator for basic EPS
Denominator for basic EPS (shares)	22,007,725	22,007,725	22,007,725	22,007,725	22,007,725	22,007,725	22,007,725	22,007,725	22,000,000.0	22,000,000.0	22,000,000.0
Denominator for diluted EPS
Denominator for diluted EPS (shares)	22,007,725	22,007,725	22,007,725	22,007,725	22,007,725	22,007,725	22,007,725	22,007,725	22,000,000.0	22,000,000.0	22,000,000.0
Basic:
EPS Basic (usd per share)	$ 1.12	$ 0.52	$ 0.29	$ 0.81	$ 1.65	$ 1.59	$ 0.34	$ 0.75	$ 2.74	$ 4.33	$ 5.33
EPS Diluted
EPS Diluted (usd per share)	$ 1.12	$ 0.52	$ 0.29	$ 0.81	$ 1.65	$ 1.59	$ 0.34	$ 0.75	$ 2.74	$ 4.33	$ 5.33