Benefit Plans - Narative (Details) (USD $)	3 Months Ended	12 Months Ended
	Aug. 31, 2012	Aug. 31, 2012	Aug. 31, 2011	Aug. 31, 2010
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan, health care benefits annual rate of increase in the per capita cost	7.50%
Defined benefit plan, health care benefits annual rate of increase in the per capita cost trend rate		5.00%
Defined contribution plan, contributions by employer		$ 20,600,000	$ 18,600,000	$ 17,300,000
Pension protection act, percentage of employers that are rural cooperatives or cooperative organizations owned by agricultural producers, criteria		85.00%
Fixed Income Securities
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan, target allocation percentage		35.00%
Equity Securities
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan, target allocation percentage		65.00%
Qualified Pension Benefits
Defined Benefit Plan Disclosure [Line Items]
Accumulated benefit obligation	628,500,000	628,500,000	466,800,000
Defined benefit plan, transfer of assets in		97,210,000
Defined benefit plan, transfer of liabilities in		84,498,000
Company contributions		28,000,000	35,000,000
Defined benefit plan, expected future benefit payments, next twelve months	36,805,000	36,805,000
Qualified Pension Benefits | Multiemployer Plans, Pension | Multiemployer Plan, Individually Insignificant Multiemployer Plans
Defined Benefit Plan Disclosure [Line Items]
Co-op Retirement Plan - Contributions of CHS		8,000		10,000
Qualified Pension Benefits | Multiemployer Plans, Pension | Co-op Retirement Plan
Defined Benefit Plan Disclosure [Line Items]
Number of employers contributing to Co-op Retirement Plan (in number of employers)	400	400
Percentage increase of employees participants		70.00%
Co-op Retirement Plan - Contributions of CHS		1,885,000	1,279,000	1,325,000
Pension Plans And Postretirement Plans, Defined Benefit, Non-Qualified
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan, expected future benefit payments, next twelve months	6,600,000	6,600,000
Other Benefits
Defined Benefit Plan Disclosure [Line Items]
Company contributions		2,035,000	1,969,000
Non-Qualified Pension Benefits
Defined Benefit Plan Disclosure [Line Items]
Accumulated benefit obligation	19,700,000	19,700,000	17,000,000
Company contributions		1,334,000	19,984,000
Defined benefit plan, expected future benefit payments, next twelve months	3,325,000	3,325,000
Agrillance LLC
Defined Benefit Plan Disclosure [Line Items]
Equity method investment, ownership percentage	(50.00%)	(50.00%)
Defined benefit plan, transfer of assets in		97,200,000
Defined benefit plan, transfer of liabilities in		84,500,000
Agrillance LLC | Transfer of Pension Plan Assets And Liabilities
Defined Benefit Plan Disclosure [Line Items]
Proceeds from joint venture, dividends or distributions, return of capital		12,700,000
Land O' Lakes | Agrillance LLC
Defined Benefit Plan Disclosure [Line Items]
Equity method investment, ownership percentage	(50.00%)	(50.00%)
Accumulated Other Comprehensive Income (Loss) | Agrillance LLC
Defined Benefit Plan Disclosure [Line Items]
Other comprehensive income (loss), pension and other postretirement benefit plans, adjustment, before tax, portion attributable to parent		$ 44,800,000
Maximum | Qualified Pension Benefits | Multiemployer Plans, Pension | Co-op Retirement Plan
Defined Benefit Plan Disclosure [Line Items]
Employer contributions as percent of total contributions of all contributing employers		5.00%
Minimum | Qualified Pension Benefits | Multiemployer Plans, Pension | Co-op Retirement Plan
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan, funded percentage	80.00%	80.00%