Long-Term Debt (Details) - USD ($)		1 Months Ended	3 Months Ended		9 Months Ended
	Sep. 28, 2015	Oct. 31, 2014	Feb. 29, 2016	Feb. 28, 2015	Feb. 29, 2016	Feb. 28, 2015	Jul. 31, 2015	May. 31, 2015
Long-term debt
Losses on early extinguishment of debt			$ (333,000)	$ (703,000)	$ (333,000)	$ (703,000)
Collateral trust bonds
Long-term debt
Proceeds from Issuance of Debt					$ 1,450,000,000
Debt Instrument, Interest Rate, Stated Percentage			2.475%		2.475%
Long-term Debt, Gross			$ 7,547,711,000		$ 7,547,711,000			$ 7,052,711,000
Collateral trust 3.05 due 2016 bonds
Long-term debt
Debt Instrument, Interest Rate, Stated Percentage			3.05%		3.05%
Repayments of Debt			$ 300,000,000
Losses on early extinguishment of debt			300,000
Unsecured notes payable | RUS
Long-term debt
Debt Instrument Fee (percent)					0.30%
Unsecured notes payable | Federal Financing Bank
Long-term debt
Proceeds from borrowings under purchase agreement					$ 400,000,000
Unsecured notes payable | Federal Financing Bank | RUS
Long-term debt
Long-term Debt, Gross			4,786,000,000		4,786,000,000			4,407,000,000
Committed loan facilities | Federal Financing Bank | Maximum
Long-term debt
Available under committed loan facilities	$ 250,000,000		350,000,000		350,000,000
Committed loan facilities | Federal Financing Bank | Loan guarantees | RUS
Long-term debt
Maturity period (duration)	20 years
Secured notes payable | Federal Agricultural Mortgage Corporation
Long-term debt
Long-term Debt, Gross			2,313,000,000		2,313,000,000			$ 1,911,000,000
Maximum borrowing capacity			$ 4,500,000,000		$ 4,500,000,000
Proceeds from borrowings under purchase agreement		$ 430,000,000
Secured notes payable | Federal Agricultural Mortgage Corporation new agr.
Long-term debt
Maximum borrowing capacity							$ 300,000,000