Equities - Narrative (Details)	12 Months Ended
	Aug. 31, 2021 USD ($) pools	Aug. 31, 2020 USD ($)	Aug. 31, 2019 USD ($)
Class of Stock [Line Items]
Estimated patronage refunds	$ (50,000,000)	$ (30,000,000)	$ (90,000,000)
Cash patronage dividends payable	$ (30,042,000)	(90,115,000)	(75,776,000)
Patronage source earnings, percentage allocated to reserves	10.00%
Capital equity certificates, number of pools | pools	2
Equity redemptions, age	70 years
Redemptions of equities	$ 79,381,000	96,438,000	85,540,000
Preferred stock dividends paid	(168,668,000)	(168,668,000)	(168,668,000)
Estimated Cash Patronage Dividends Payable	50,000,000
futurePaymentsForRepurchaseOfOtherEquity	(100,000,000)
Total Patronage refunds, estimated	(280,300,000)
nonqualified patronage, estimated	230,300,000
Class B, Series 1 Preferred Stock [Member]
Class of Stock [Line Items]
Preferred Stock, Redemption Amount	536,500,000
Capital Reserves
Class of Stock [Line Items]
Estimated patronage refunds	(280,290,000)	(241,970,000)	(562,398,000)
Nonqualified Equity Certificates
Class of Stock [Line Items]
Estimated patronage refunds	230,290,000	$ 211,970,000	$ 472,398,000
Qualified Equity Certificates
Class of Stock [Line Items]
Estimated patronage refunds	$ 0