Quarterly Financial Information (Unaudited) - Impacts of the Restatement Adjustments to the Previously Reported Consolidated Statements of Comprehensive Income (Details) - USD ($) $ in Thousands	3 Months Ended								6 Months Ended		9 Months Ended		12 Months Ended
	Aug. 31, 2018	May 31, 2018	Feb. 28, 2018	Nov. 30, 2017	Aug. 31, 2017	May 31, 2017	Feb. 28, 2017	Nov. 30, 2016	Feb. 28, 2018	Feb. 28, 2017	May 31, 2018	May 31, 2017	Aug. 31, 2018	Aug. 31, 2017	Aug. 31, 2016
Error Corrections and Prior Period Adjustments Restatement [Line Items]
Net income (loss)	$ 240,545	$ 181,620	$ 165,959	$ 187,182	$ (74,327)	$ (72,488)	$ 14,617	$ 203,156	$ 353,141	$ 217,773	$ 534,761	$ 145,285	$ 775,306	$ 70,958	$ 383,026
Postretirement benefit plan activity	11,913	3,417	3,142	1,594	22,103	3,636	3,724	3,239	4,736	6,963	8,153	10,599	20,066	32,702	6,583
Unrealized net gain (loss) on available for sale investments	(16,628)	6,286	3,554	3,640	2,758	(118)	968	777	7,194	1,745	13,480	1,627	(3,148)	4,385	1,500
Cash flow hedges	1,068	413	1,063	(4)	249	375	964	654	1,059	1,618	1,472	1,993	2,540	2,242	(3,872)
Foreign currency translation adjustment	(1,974)	(10,188)	2,352	(2,211)	3,098	(1,369)	8,187	(18,075)	141	(9,888)	(10,047)	(11,257)	(12,021)	(8,159)	(2,904)
Other comprehensive income (loss), net of tax	(5,621)	(72)	10,111	3,019	28,208	2,524	13,843	(13,405)	13,130	438	13,058	2,962	7,437	31,170	1,307
Comprehensive income	234,924	181,548	176,070	190,201	(46,119)	(69,964)	28,460	189,751	366,271	218,211	547,819	148,247	782,743	102,128	384,333
Less comprehensive income attributable to noncontrolling interests	98	(187)	(48)	(464)	123	(955)	406	(208)	(512)	198	(699)	(757)	(601)	(634)	(223)
Comprehensive income attributable to CHS Inc.	$ 234,826	181,735	176,118	190,665	(46,242)	(69,009)	28,054	189,959	366,783	218,013	548,518	149,004	$ 783,344	102,762	384,556
Postretirement benefit plan, tax expense (benefit)		1,424	1,309	2,620	12,108	2,257	2,312	2,011	3,929	4,323	5,353	6,580
Unrealized net gain (loss) on available for sale investments, tax expense (benefit)		2,620	1,481	404	1,722	(72)	600	482	1,885	1,083	4,505	1,010
Cash flow hedges, tax expense (benefit)		172	443	(2)	155	233	598	406	441	1,005	613	1,238
Foreign currency translation adjustment, tax expense (benefit)		(254)	422	(443)	542	(334)	(204)	(209)	(21)	5	(275)	(329)
As Previously Reported
Error Corrections and Prior Period Adjustments Restatement [Line Items]
Net income (loss)		229,146	166,626	179,619	(50,552)	(46,140)	14,973	208,942	346,245	223,915	575,391	177,775		127,223	423,969
Postretirement benefit plan activity		3,417	3,141	4,196	19,501	3,635	3,724	3,239	7,338	6,963	10,755	10,599		30,100	6,583
Unrealized net gain (loss) on available for sale investments		6,286	3,554	3,640	2,758	(117)	968	777	7,194	1,744	13,480	1,627		4,385	1,500
Cash flow hedges		413	1,063	(4)	249	375	963	654	1,059	1,618	1,472	1,993		2,242	(3,872)
Foreign currency translation adjustment		(11,617)	2,461	(2,607)	3,522	(2,151)	9,123	(19,164)	(146)	(10,041)	(11,763)	(12,193)		(8,671)	(1,730)
Other comprehensive income (loss), net of tax		(1,501)	10,219	5,225	26,030	1,742	14,778	(14,494)	15,445	284	13,944	2,026		28,056	2,481
Comprehensive income		227,645	176,845	184,844	(24,522)	(44,398)	29,751	194,448	361,690	224,199	589,335	179,801		155,279	426,450
Less comprehensive income attributable to noncontrolling interests		(187)	(48)	(464)	123	(955)	406	(208)	(512)	198	(699)	(757)		(634)	(223)
Comprehensive income attributable to CHS Inc.		227,832	176,893	185,308	(24,645)	(43,443)	29,345	194,656	362,202	224,001	590,034	180,558		155,913	426,673
Restatement Adjustments
Error Corrections and Prior Period Adjustments Restatement [Line Items]
Net income (loss)		(47,526)	(667)	7,563	(23,775)	(26,348)	(356)	(5,786)	6,896	(6,142)	(40,630)	(32,490)		(56,265)	(40,943)
Postretirement benefit plan activity		0	1	(2,602)	2,602	1	0	0	(2,602)	0	(2,602)	0		2,602	0
Unrealized net gain (loss) on available for sale investments		0	0	0	0	(1)	0	0	0	1	0	0		0	0
Cash flow hedges		0	0	0	0	0	1	0	0	0	0	0		0	0
Foreign currency translation adjustment		1,429	(109)	396	(424)	782	(936)	1,089	287	153	1,716	936		512	(1,174)
Other comprehensive income (loss), net of tax		1,429	(108)	(2,206)	2,178	782	(935)	1,089	(2,315)	154	(886)	936		3,114	(1,174)
Comprehensive income		(46,097)	(775)	5,357	(21,597)	(25,566)	(1,291)	(4,697)	4,581	(5,988)	(41,516)	(31,554)		(53,151)	(42,117)
Less comprehensive income attributable to noncontrolling interests		0	0	0	0	0	0	0	0	0	0	0		0	0
Comprehensive income attributable to CHS Inc.		(46,097)	(775)	5,357	(21,597)	(25,566)	(1,291)	(4,697)	4,581	(5,988)	(41,516)	(31,554)		(53,151)	(42,117)
Restatement Adjustments | Freight Derivatives and Related Misstatements
Error Corrections and Prior Period Adjustments Restatement [Line Items]
Net income (loss)		(24,700)	(22,600)	(1,200)	(25,200)	(22,800)	200	600	(23,800)	800	(48,500)	(22,100)		(47,300)	(9,900)
Restatement Adjustments | Other Misstatements
Error Corrections and Prior Period Adjustments Restatement [Line Items]
Net income (loss)		$ (22,800)	$ 21,900	$ 8,800	$ 1,400	$ (3,600)	(600)	$ (6,400)	$ 30,700	$ (6,900)	$ 7,900	$ (10,400)		$ (9,000)	$ (31,000)
Restatement Adjustments | Freight Derivatives And Related Misstatements, Foreign Currency Impact [Member]
Error Corrections and Prior Period Adjustments Restatement [Line Items]
Net income (loss)							$ 200