Quarterly Financial Information (Unaudited) - 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
Quarterly Financial Information Disclosure [Abstract]
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
Other comprehensive income (loss), net of tax:
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