Commitments and Contingencies - Narrative (Details) (USD $)	12 Months Ended
	Aug. 31, 2013	Aug. 31, 2012	Aug. 31, 2011
Property, Plant and Equipment [Line Items]
Loss Contingency, Range of Possible Loss, Minimum	$ 14,400,000
Loss Contingency, Range of Possible Loss, Maximum	39,700,000
Loss Contingency, Loss in Period	25,000,000
Grain Storage [Abstract]
Inventory, held for third parties	454,900,000	441,300,000
Guarantor Obligations, Maximum Exposure, Undiscounted	1,000,000,000
Guarantees [Abstract]
Guarantor obligations, current carrying value	39,800,000
Lease Commitments
Number of rail cars under operating lease commitments	2,600
Operating leases, rent expense, net	81,500,000	74,600,000	66,200,000
Unrecorded unconditional purchase obligation	$ 5,382,472,000	$ 6,300,000,000
Minimum
Lease Commitments
Operating lease terms	1 year
Maximum
Lease Commitments
Operating lease terms	13 years