Fair Value of Financial Instruments (Details Textual) (USD $)																											9 Months Ended
	Feb. 28, 2014	May 31, 2013	Feb. 28, 2014 Subordinated Deferrable Debt	May 31, 2013 Subordinated Deferrable Debt	Feb. 28, 2014 Subordinated certificates	May 31, 2013 Subordinated certificates	Feb. 28, 2014 Fair Value, Inputs, Level 1	May 31, 2013 Fair Value, Inputs, Level 1	Feb. 28, 2014 Fair Value, Inputs, Level 1 Subordinated Deferrable Debt	May 31, 2013 Fair Value, Inputs, Level 1 Subordinated Deferrable Debt	Feb. 28, 2014 Fair Value, Inputs, Level 1 Commercial Paper Sold Directly to Members at Par Commercial Paper Sold Directly to Non Members at Par and Select Notes	May 31, 2013 Fair Value, Inputs, Level 1 Commercial Paper Sold Directly to Members at Par Commercial Paper Sold Directly to Non Members at Par and Select Notes	Feb. 28, 2014 Fair Value, Inputs, Level 2	May 31, 2013 Fair Value, Inputs, Level 2	Feb. 28, 2014 Fair Value, Inputs, Level 2 Subordinated Deferrable Debt	May 31, 2013 Fair Value, Inputs, Level 2 Subordinated Deferrable Debt	Feb. 28, 2014 Fair Value, Inputs, Level 2 Commercial Paper Sold Directly to Members at Par Commercial Paper Sold Directly to Non Members at Par and Select Notes	May 31, 2013 Fair Value, Inputs, Level 2 Commercial Paper Sold Directly to Members at Par Commercial Paper Sold Directly to Non Members at Par and Select Notes	Feb. 28, 2014 Fair Value, Inputs, Level 2 Collateral Trust Bonds and Medium Term Notes	May 31, 2013 Fair Value, Inputs, Level 2 Collateral Trust Bonds and Medium Term Notes	Feb. 28, 2014 Fair Value, Inputs, Level 3	May 31, 2013 Fair Value, Inputs, Level 3	Feb. 28, 2014 Fair Value, Inputs, Level 3 Subordinated certificates	May 31, 2013 Fair Value, Inputs, Level 3 Subordinated certificates	Feb. 28, 2014 Fair Value, Inputs, Level 3 Notes Payable, Other Payables	May 31, 2013 Fair Value, Inputs, Level 3 Notes Payable, Other Payables	Feb. 28, 2014 Maximum	Feb. 28, 2014 Minimum
Maturity Period of Short Term Debt for which Fair Value is Estimated Based on Quoted Market Rates																											90 days	90 days
Cash and Cash Equivalents, Fair Value Disclosure							$ 843,000,000	$ 177,000,000
Restricted Cash and Cash Equivalents	7,256,000	7,696,000					7,000,000	8,000,000
Investments, Fair Value Disclosure							29,000,000	32,000,000
Time Deposits, at Carrying Value	700,000,000	700,000,000											700,000,000	700,000,000
Subordinated Long-term Debt, Noncurrent			400,000,000	400,000,000	1,486,965,000	1,729,226,000			4,000,000	4,000,000					372,000,000	404,000,000							1,487,000,000	1,881,000,000
Loans Receivable, Fair Value Disclosure																					21,016,000,000	21,318,000,000
Debt Service Reserve	39,353,000	39,803,000					39,000,000	40,000,000
Debt, Current	6,541,987,000	7,719,483,000									3,353,000,000	2,840,000,000					1,433,000,000	1,210,000,000	1,495,000,000	2,912,000,000					267,000,000	789,000,000
Other Long-term Debt, Noncurrent																			8,424,000,000	7,410,000,000					5,656,000,000	4,746,000,000
Guarantees, Fair Value Disclosure																					26,000,000	28,000,000
Derivative assets	261,598,000	257,878,000					0	0					261,598,000	257,878,000
Derivative liabilities	$ 380,518,000	$ 475,278,000					$ 0	$ 0					$ 380,518,000	$ 475,278,000