Loans and Commitments (Details Textual) (USD $)	9 Months Ended		3 Months Ended		9 Months Ended		12 Months Ended
	Feb. 28, 2014	May 31, 2013	Feb. 28, 2014 Nonperforming Restructure Loans [Member]	Feb. 28, 2013 Nonperforming Restructure Loans [Member]	Feb. 28, 2014 Nonperforming Restructure Loans [Member]	Feb. 28, 2014 Performing Financing Receivable	May 31, 2013 Performing Financing Receivable	Feb. 28, 2014 Commitments to Extend Credit		May 31, 2013 Commitments to Extend Credit		Feb. 28, 2014 Commitments to Extend Credit Performing Financing Receivable		May 31, 2013 Commitments to Extend Credit Performing Financing Receivable		Feb. 28, 2014 Unadvanced commitments subject to material adverse change clauses	May 31, 2013 Unadvanced commitments subject to material adverse change clauses	Feb. 28, 2014 Unadvanced commitments not subject to material adverse change clauses	May 31, 2013 Unadvanced commitments not subject to material adverse change clauses
Financing Receivable, Recorded Investment, Past Due [Line Items]
Other Commitment		$ 39,000,000						$ 13,544,658,000	[1],[2]	$ 13,422,748,000	[1],[2]	$ 0	[2]	$ 5,000,000	[2]	$ 2,248,762,000	$ 11,720,000,000	$ 2,249,000,000	$ 1,703,000,000
Loans and Leases Receivable Commercial Net of Deferred Income Additions						8,000,000	47,000,000
Amount of Financing Receivable Refinanced						14,000,000
Loans and Leases Receivable Commercial, Net of Deferred Income, Percentage	100.00%	100.00%				0.04%	0.23%
Intercompany Loans, Description	At February 28, 2014 and May 31, 2013, nonperforming loans totaled $11 million or 0.05 percent, of loans outstanding and $15 million or 0.08 percent, of loans outstanding
Deferred Origination Cost	10,000,000	10,000,000
Interest and Other Income, Total			$ 0	$ 400,000	$ 100,000

[1] Includes nonperforming and restructured loans.

[2] The interest rate on unadvanced commitments is not set until drawn, therefore, the long-term unadvanced loan commitments have been classified in this table as variable-rate unadvanced commitments. However, at the time of the advance, the borrower may select a fixed or a variable rate on the new loan.