Consolidated Statements of Changes in Equities - USD ($) $ in Thousands	3 Months Ended	12 Months Ended
	Aug. 31, 2018	Aug. 31, 2019	Aug. 31, 2018	Aug. 31, 2017
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Balance		$ 8,165,028	$ 7,705,640	$ 7,759,159
Reversal of prior year patronage and redemption estimates		153,941	6,058	162,439
Distribution of patronage refunds		(75,776)		(103,879)
Redemptions of equities		85,540	6,725	(37,390)
Equities issued				3,194
Preferred stock dividends		(168,668)	(168,668)	(167,643)
Other, net		(2,800)	(4,020)	2,368
Net income (loss)		828,057	775,306	70,958
Other comprehensive income (loss), net of tax		(22,312)	7,437	31,170
Reclassification of tax effects to capital reserves		0
Estimated patronage refunds		90,000	75,000
Estimated equity redemptions		(90,000)	(75,000)	(10,000)
Balance	$ 8,165,028	8,617,530	8,165,028	7,705,640
Capital Equity Certificates
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Balance		3,837,580	3,906,426	3,918,711
Reversal of prior year patronage and redemption estimates		78,941	6,058	(95,019)
Distribution of patronage refunds				153,589
Redemptions of equities		(70,859)	(6,064)	(35,041)
Equities issued				3,194
Capital equity certificates redeemed with preferred stock				(19,985)
Other, net		(2,169)	(3,840)	(9,023)
Estimated equity redemptions		(90,000)	(65,000)	(10,000)
Balance	3,837,580	3,753,493	3,837,580	3,906,426
Nonpatronage Equity Certificates
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Balance		29,498	29,836	22,894
Redemptions of equities		(409)	(185)	(389)
Other, net		(15)	(153)	7,331
Balance	29,498	29,074	29,498	29,836
Nonqualified Equity Certificates
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Balance		742,378	405,387	281,767
Reversal of prior year patronage and redemption estimates		(345,330)	(126,333)
Distribution of patronage refunds		352,980	(128,831)
Redemptions of equities		(14,272)	(476)	(1,960)
Other, net		(1,844)	(361)	(753)
Estimated patronage refunds		472,398	345,330	(126,333)
Estimated equity redemptions			(10,000)
Balance	742,378	1,206,310	742,378	405,387
Preferred Stock
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Balance		2,264,038	2,264,038	2,244,132
Capital equity certificates redeemed with preferred stock				19,960
Other, net				(54)
Balance	2,264,038	2,264,038	2,264,038	2,264,038
Accumulated Other Comprehensive Loss
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Balance		(199,915)	(180,360)	(211,530)
Other comprehensive income (loss), net of tax		(22,312)	7,437	31,170
TaxCutsAndJobsActof2017ReclassfromAOCItoRetainedEarningsTaxEffect			(26,992)
Reclassification of tax effects to capital reserves		(4,706)	(26,992)
Balance	(199,915)	(226,933)	(199,915)	(180,360)
Capital Reserves
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Balance		1,482,003	1,267,808	1,488,999
Reversal of prior year patronage and redemption estimates		420,330	126,333	257,458
Distribution of patronage refunds		(428,756)	(128,831)	(257,468)
Capital equity certificates redeemed with preferred stock				25
Preferred stock dividends		(168,668)	(168,668)	(167,643)
Other, net		7,061	2,792	1,178
Net income (loss)		829,880	775,907	71,592
TaxCutsAndJobsActof2017ReclassfromAOCItoRetainedEarningsTaxEffect			26,992
Reclassification of tax effects to capital reserves	27,000	4,706
Estimated patronage refunds		(562,398)	(420,330)	(126,333)
Balance	1,482,003	1,584,158	1,482,003	1,267,808
Noncontrolling Interests
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Balance		9,446	12,505	14,186
Other, net		(233)	(2,458)	(1,047)
Net income (loss)		(1,823)	(601)	(634)
Balance	$ 9,446	$ 7,390	$ 9,446	$ 12,505