Consolidated Statements of Changes in Equities - USD ($) $ in Thousands	12 Months Ended
	Aug. 31, 2018	Aug. 31, 2017	Aug. 31, 2016
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Balance	$ 7,705,640	$ 7,759,159	$ 7,551,439
Reversal of prior year patronage and redemption estimates	6,058	162,439	357,427
Distribution of patronage refunds		(103,879)	(251,740)
Redemptions of equities	(6,725)	(37,390)	(23,911)
Equities issued		3,194	23,258
Preferred stock dividends	(168,668)	(167,643)	(122,824)
Other, net	(4,020)	(2,368)	3,616
Net income (loss)	775,306	70,958	383,026
Other comprehensive income (loss), net of tax	7,437	31,170	1,307
Reclassification of tax effects to retained earnings	0
Estimated patronage refunds	(75,000)		(103,879)
Estimated equity redemptions	(75,000)	(10,000)	(58,560)
Balance	8,165,028	7,705,640	7,759,159
Capital Equity Certificates
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Balance	3,906,426	3,918,711	3,793,897
Reversal of prior year patronage and redemption estimates	6,058	(95,019)	(268,017)
Distribution of patronage refunds		153,589	375,506
Redemptions of equities	(6,064)	(35,041)	(22,948)
Equities issued		3,194	23,258
Capital equity certificates redeemed with preferred stock		(19,985)	(76,756)
Other, net	(3,840)	(9,023)	(1,248)
Estimated patronage refunds			153,579
Estimated equity redemptions	(65,000)	(10,000)	(58,560)
Balance	3,837,580	3,906,426	3,918,711
Nonpatronage Equity Certificates
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Balance	29,836	22,894	23,057
Redemptions of equities	(185)	(389)	(143)
Other, net	(153)	7,331	(20)
Balance	29,498	29,836	22,894
Nonqualified Equity Certificates
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Balance	405,387	281,767	282,928
Reversal of prior year patronage and redemption estimates	(126,333)
Distribution of patronage refunds	128,831
Redemptions of equities	(476)	(1,960)	(820)
Other, net	(361)	(753)	(341)
Estimated patronage refunds	345,330	126,333
Estimated equity redemptions	(10,000)
Balance	742,378	405,387	281,767
Preferred Stock
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Balance	2,264,038	2,244,132	2,167,540
Capital equity certificates redeemed with preferred stock		19,960	76,756
Other, net		(54)	(164)
Balance	2,264,038	2,264,038	2,244,132
Accumulated Other Comprehensive Loss
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Balance	(180,360)	(211,530)	(212,837)
Other comprehensive income (loss), net of tax	7,437	31,170	1,307
Reclassification of tax effects to retained earnings	(26,992)
Balance	(199,915)	(180,360)	(211,530)
Capital Reserves
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Balance	1,267,808	1,488,999	1,485,433
Reversal of prior year patronage and redemption estimates	126,333	257,458	625,444
Distribution of patronage refunds	(128,831)	(257,468)	(627,246)
Capital equity certificates redeemed with preferred stock		25
Preferred stock dividends	(168,668)	(167,643)	(122,824)
Other, net	2,792	1,178	2,401
Net income (loss)	775,907	71,592	383,249
Reclassification of tax effects to retained earnings	26,992
Estimated patronage refunds	(420,330)	(126,333)	(257,458)
Balance	1,482,003	1,267,808	1,488,999
Noncontrolling Interests
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Balance	12,505	14,186	11,421
Other, net	(2,458)	(1,047)	2,988
Net income (loss)	(601)	(634)	(223)
Balance	9,446	12,505	14,186
As Previously Reported
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Balance	7,905,825	7,866,250	7,669,411
Net income (loss)		127,223	423,969
Other comprehensive income (loss), net of tax		28,056	2,481
Balance		7,905,825	7,866,250
As Previously Reported | Capital Equity Certificates
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Balance	3,906,426	3,932,513	3,793,897
Balance		3,906,426	3,932,513
As Previously Reported | Nonpatronage Equity Certificates
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Balance	29,836	22,894	23,057
Balance		29,836	22,894
As Previously Reported | Nonqualified Equity Certificates
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Balance	405,387	281,767	282,928
Balance		405,387	281,767
As Previously Reported | Preferred Stock
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Balance	2,264,038	2,244,132	2,167,540
Balance		2,264,038	2,244,132
As Previously Reported | Accumulated Other Comprehensive Loss
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Balance	(183,670)	(211,726)	(214,207)
Balance		(183,670)	(211,726)
As Previously Reported | Capital Reserves
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Balance	1,471,217	1,582,380	1,604,670
Balance		1,471,217	1,582,380
As Previously Reported | Noncontrolling Interests
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Balance	12,591	14,290	11,526
Balance		12,591	14,290
Cumulative restatement adjustments
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Balance	(200,185)	(107,091)	(117,972)
Net income (loss)		(56,265)	(40,943)
Other comprehensive income (loss), net of tax		3,114	(1,174)
Balance		(200,185)	(107,091)
Cumulative restatement adjustments | Capital Equity Certificates
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Balance	0	(13,802)	0
Balance		0	(13,802)
Cumulative restatement adjustments | Nonpatronage Equity Certificates
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Balance	0	0	0
Balance		0	0
Cumulative restatement adjustments | Nonqualified Equity Certificates
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Balance	0	0	0
Balance		0	0
Cumulative restatement adjustments | Preferred Stock
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Balance	0	0	0
Balance		0	0
Cumulative restatement adjustments | Accumulated Other Comprehensive Loss
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Balance	3,310	196	1,370
Balance		3,310	196
Cumulative restatement adjustments | Capital Reserves
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Balance	(203,409)	(93,381)	(119,237)
Balance		(203,409)	(93,381)
Cumulative restatement adjustments | Noncontrolling Interests
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Balance	$ (86)	(104)	(105)
Balance		$ (86)	$ (104)