Loans and Commitments (Details 2) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	May 31, 2014		May 31, 2013
Unadvanced commitments
Notional maturities of committed lines of credit
Total unadvanced commitments	$ 13,912,078	[1],[2],[3]	$ 13,422,748	[1],[2],[3]
Maximum period of commitments to fully fund agreements which have not yet been advanced	5 years
Unadvanced commitments not subject to material adverse change clauses
Notional maturities of committed lines of credit
2015	19,238
2016	61,000
2017	456,855
2018	678,839
2019	1,058,456
Total unadvanced commitments	2,274,388		1,703,000
Maximum period of commitments to fully fund agreements which have not yet been advanced	5 years
Unadvanced commitments subject to material adverse change clauses
Notional maturities of committed lines of credit
Total unadvanced commitments	$ 11,638,000		$ 11,720,000

[1] Includes the unpaid principal balance excluding deferred origination costs.

[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.

[3] Includes nonperforming and restructured loans.