Derivative Financial Instruments and Hedging Activities - Purchase and Sale Contracts (Details) - Not Designated as Hedging Instrument t in Thousands, T in Thousands, MMBtu in Thousands, Bushels in Thousands, Barrels in Thousands	May 31, 2019 T t Bushels MMBtu Barrels	Aug. 31, 2018 T t Bushels MMBtu Barrels
Grain and oilseed - bushels | Long [Member]
Derivative [Line Items]
Derivative, Nonmonetary Notional Amount | Bushels	693,978	715,866
Grain and oilseed - bushels | Short [Member]
Derivative [Line Items]
Derivative, Nonmonetary Notional Amount | Bushels	865,956	929,873
Energy products - barrels | Long [Member]
Derivative [Line Items]
Derivative, Nonmonetary Notional Amount | Barrels	16,223	17,011
Energy products - barrels | Short [Member]
Derivative [Line Items]
Derivative, Nonmonetary Notional Amount | Barrels	5,930	8,329
Processed grain and oilseed - tons | Long [Member]
Derivative [Line Items]
Derivative, Nonmonetary Notional Amount	406	1,064
Processed grain and oilseed - tons | Short [Member]
Derivative [Line Items]
Derivative, Nonmonetary Notional Amount	2,208	2,875
Crop nutrients - tons | Long [Member]
Derivative [Line Items]
Derivative, Nonmonetary Notional Amount	19	11
Crop nutrients - tons | Short [Member]
Derivative [Line Items]
Derivative, Nonmonetary Notional Amount	72	76
Ocean freight - metric tons | Long [Member]
Derivative [Line Items]
Derivative, Nonmonetary Notional Amount | t	125	227
Ocean freight - metric tons | Short [Member]
Derivative [Line Items]
Derivative, Nonmonetary Notional Amount | t	95	45
Natural gas - MMBtu | Long [Member]
Derivative [Line Items]
Derivative, Nonmonetary Notional Amount | MMBtu	0	610
Natural gas - MMBtu | Short [Member]
Derivative [Line Items]
Derivative, Nonmonetary Notional Amount | MMBtu	0	0