Summary of Significant Accounting Policies (Details Textual) (USD $)	9 Months Ended
	Feb. 28, 2014	Feb. 28, 2013	May 31, 2013
Variable Interest Entities
Loans outstanding	$ 20,589,024,000	$ 19,337,737,000	$ 20,251,549,000
Loans Receivable Cost of Loans Sold	106,000,000	121,000,000
Deferred Loan Conversion Fees	74,000,000	21,000,000
Decrease in Other Liabilities Due to Prior Period Misclassification	11,500,000
Consolidated variable interest entities | RTFC
Variable Interest Entities
Guarantee amount	2,000,000
Total assets including loans outstanding to members	577,000,000
Loans outstanding	455,000,000
Maximum amount committed to extend loan	4,000,000,000
Commitment outstanding	441,000,000
Loans outstanding	779,000,000
Consolidated variable interest entities | NCSC
Variable Interest Entities
Guarantee amount	121,000,000
Maximum potential exposure	128,000,000
Total assets including loans outstanding to members	804,000,000
Loans outstanding	763,000,000
Commitment outstanding	3,000,000,000
Loans outstanding	884,000,000
Credit enhancements	$ 121,000,000