Consolidated Statements of Changes in Equities - USD ($) $ in Thousands	12 Months Ended
	Aug. 31, 2020	Aug. 31, 2019	Aug. 31, 2018
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Balance	$ 8,617,530	$ 8,165,028	$ 7,705,640
Reversal of prior year patronage and redemption estimates	180,000	153,941	6,058
Cash patronage dividends payable	(90,115)	(75,776)	0
Redemptions of equities	96,438	85,540	(6,725)
Preferred stock dividends	(168,668)	(168,668)	(168,668)
Cumulative effect adjustment asc topic 842	25,320
Other, net	2,074	2,800	4,020
Net income	423,609	828,057	775,306
Other comprehensive income, net of tax	(6,991)	(22,312)	7,437
Estimated patronage refunds	(30,000)	(90,000)	(75,000)
Estimated equity redemptions	(33,000)	(90,000)	(75,000)
Balance	8,819,173	8,617,530	8,165,028
Capital Equity Certificates
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Balance	3,753,493	3,837,580	3,906,426
Reversal of prior year patronage and redemption estimates	80,000	78,941	6,058
Redemptions of equities	(80,133)	(70,859)	(6,064)
Other, net	(1,173)	(2,169)	(3,840)
Estimated equity redemptions	(28,000)	(90,000)	(65,000)
Balance	3,724,187	3,753,493	3,837,580
Nonpatronage Equity Certificates
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Balance	29,074	29,498	29,836
Redemptions of equities	(340)	(409)	(185)
Other, net	(7)	(15)	(153)
Balance	28,727	29,074	29,498
Nonqualified Equity Certificates
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Balance	1,206,310	742,378	405,387
Reversal of prior year patronage and redemption estimates	(462,398)	(345,330)	(126,333)
Distribution of patronage refunds	474,407	352,980	128,831
Redemptions of equities	(15,965)	(14,272)	(476)
Other, net	(628)	(1,844)	(361)
Estimated patronage refunds	211,970	472,398	345,330
Estimated equity redemptions	(5,000)	0	(10,000)
Balance	1,408,696	1,206,310	742,378
Preferred Stock
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Balance	2,264,038	2,264,038	2,264,038
Balance	2,264,038	2,264,038	2,264,038
Accumulated Other Comprehensive Loss
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Balance	(226,933)	(199,915)	(180,360)
Other comprehensive income, net of tax	(6,991)	(22,312)	7,437
TaxCutsAndJobsActof2017ReclassfromAOCItoRetainedEarningsTaxEffect		(4,706)	(26,992)
Balance	(233,924)	(226,933)	(199,915)
Capital Reserves
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Balance	1,584,158	1,482,003	1,267,808
Reversal of prior year patronage and redemption estimates	562,398	420,330	126,333
Distribution of patronage refunds	(564,522)	(428,756)	(128,831)
Preferred stock dividends	(168,668)	(168,668)	(168,668)
Cumulative effect adjustment asc topic 842	25,320
Other, net	(1,008)	7,061	2,792
Net income	422,439	829,880	775,907
TaxCutsAndJobsActof2017ReclassfromAOCItoRetainedEarningsTaxEffect		4,706	26,992
Estimated patronage refunds	241,970	562,398	420,330
Balance	1,618,147	1,584,158	1,482,003
Noncontrolling Interests
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Balance	7,390	9,446	12,505
Other, net	742	(233)	(2,458)
Net income	1,170	(1,823)	(601)
Balance	$ 9,302	$ 7,390	$ 9,446