Derivative Financial Instruments and Hedging Activities Purchase and Sale Contracts (Details) - Not Designated as Hedging Instrument [Member] t in Thousands, rail_car in Thousands, T in Thousands, MMBtu in Thousands, Bushels in Thousands, Barrels in Thousands	May 31, 2017 T rail_car t Bushels MMBtu Barrels	Aug. 31, 2016 T rail_car t Bushels MMBtu Barrels
Grain and oilseed - bushels | Long [Member]
Purchase and Sales Contracts [Line Items]
Derivative, Nonmonetary Notional Amount | Bushels	663,358	774,279
Grain and oilseed - bushels | Short [Member]
Purchase and Sales Contracts [Line Items]
Derivative, Nonmonetary Notional Amount | Bushels	860,178	995,396
Energy products - barrels | Long [Member]
Purchase and Sales Contracts [Line Items]
Derivative, Nonmonetary Notional Amount | Barrels	13,694	14,740
Energy products - barrels | Short [Member]
Purchase and Sales Contracts [Line Items]
Derivative, Nonmonetary Notional Amount | Barrels	8,151	6,470
Processed grain and oilseed - tons | Long [Member]
Purchase and Sales Contracts [Line Items]
Derivative, Nonmonetary Notional Amount	327	541
Processed grain and oilseed - tons | Short [Member]
Purchase and Sales Contracts [Line Items]
Derivative, Nonmonetary Notional Amount	2,188	2,060
Crop nutrients - tons | Long [Member]
Purchase and Sales Contracts [Line Items]
Derivative, Nonmonetary Notional Amount	70	108
Crop nutrients - tons | Short [Member]
Purchase and Sales Contracts [Line Items]
Derivative, Nonmonetary Notional Amount	241	135
Ocean and barge freight - metric tons | Long [Member]
Purchase and Sales Contracts [Line Items]
Derivative, Nonmonetary Notional Amount | t	4,110	4,406
Ocean and barge freight - metric tons | Short [Member]
Purchase and Sales Contracts [Line Items]
Derivative, Nonmonetary Notional Amount | t	876	877
Rail freight - rail cars | Long [Member]
Purchase and Sales Contracts [Line Items]
Derivative, Nonmonetary Notional Amount | rail_car	210	205
Rail freight - rail cars | Short [Member]
Purchase and Sales Contracts [Line Items]
Derivative, Nonmonetary Notional Amount | rail_car	97	79
Natural gas - MMBtu | Long [Member]
Purchase and Sales Contracts [Line Items]
Derivative, Nonmonetary Notional Amount | MMBtu	3,275	3,550
Natural gas - MMBtu | Short [Member]
Purchase and Sales Contracts [Line Items]
Derivative, Nonmonetary Notional Amount | MMBtu	0	300