Long-Term Debt (Details) (USD $) In Thousands, unless otherwise specified	Feb. 28, 2014	May 31, 2013
Long-term debt
Total long-term debt	$ 12,902,920	$ 10,696,433
Unsecured long-term debt
Long-term debt
Total long-term debt	5,933,024	5,418,741
Unsecured medium-term notes
Long-term debt
Long-term debt before unamortized discount	1,902,269	1,711,214
Unamortized discount	(616)	(627)
Total long-term debt	1,901,653	1,710,587
Medium-term notes sold through dealers
Long-term debt
Long-term debt before unamortized discount	1,783,171	1,528,424
Medium-term notes sold to members
Long-term debt
Long-term debt before unamortized discount	119,098	182,790
Unsecured notes payable
Long-term debt
Long-term debt before unamortized discount	4,032,167	3,709,074
Unamortized discount	(796)	(920)
Total long-term debt	4,031,371	3,708,154
Secured long-term debt
Long-term debt
Total long-term debt	6,969,896	5,277,692
Collateral trust bonds
Long-term debt
Long-term debt before unamortized discount	5,634,372	4,639,372
Unamortized discount	(178,564)	(181,640)
Total long-term debt	5,455,808	4,457,732
Secured notes payable
Long-term debt
Total long-term debt	$ 1,514,088	$ 819,960