Loans and Commitments (Details 5) (USD $) In Thousands, unless otherwise specified	Aug. 31, 2013	May 31, 2013	Aug. 31, 2012
Loan Security
Total loans outstanding	$ 20,405,091	$ 20,296,317	$ 19,467,736
Loans receivable as a percentage of total loan	100.00%	100.00%
CFC
Loan Security
Total loans outstanding	19,220,289	19,019,817
RTFC
Loan Security
Total loans outstanding	479,769	503,359
NCSC
Loan Security
Total loans outstanding	705,033	773,141
Secured
Loan Security
Total loans outstanding	18,154,454	18,053,059
Loans receivable as a percentage of total loan	89.00%	89.00%
Secured | CFC
Loan Security
Total loans outstanding	17,240,266	17,049,029
Loans receivable as a percentage of total loan	90.00%	90.00%
Secured | RTFC
Loan Security
Total loans outstanding	459,163	482,647
Loans receivable as a percentage of total loan	96.00%	96.00%
Secured | NCSC
Loan Security
Total loans outstanding	455,025	521,383
Loans receivable as a percentage of total loan	65.00%	67.00%
Unsecured
Loan Security
Total loans outstanding	2,250,637	2,243,258
Loans receivable as a percentage of total loan	11.00%	11.00%
Unsecured | CFC
Loan Security
Total loans outstanding	1,980,023	1,970,788
Loans receivable as a percentage of total loan	10.00%	10.00%
Unsecured | RTFC
Loan Security
Total loans outstanding	20,606	20,712
Loans receivable as a percentage of total loan	4.00%	4.00%
Unsecured | NCSC
Loan Security
Total loans outstanding	250,008	251,758
Loans receivable as a percentage of total loan	35.00%	33.00%
Long-term fixed-rate loans
Loan Security
Total loans outstanding	18,208,107	17,918,268
Long-term fixed-rate loans | Secured
Loan Security
Total loans outstanding	17,116,916	16,871,594
Loans receivable as a percentage of total loan	94.00%	94.00%
Long-term fixed-rate loans | Unsecured
Loan Security
Total loans outstanding	1,091,191	1,046,674
Loans receivable as a percentage of total loan	6.00%	6.00%
Long-term variable-rate loans
Loan Security
Total loans outstanding	681,573	782,006
Long-term variable-rate loans | Secured
Loan Security
Total loans outstanding	577,880	676,075
Loans receivable as a percentage of total loan	85.00%	86.00%
Long-term variable-rate loans | Unsecured
Loan Security
Total loans outstanding	103,693	105,931
Loans receivable as a percentage of total loan	15.00%	14.00%
Loans guaranteed by RUS
Loan Security
Total loans outstanding	209,560	210,815
Loans guaranteed by RUS | Secured
Loan Security
Total loans outstanding	209,560	210,815
Loans receivable as a percentage of total loan	100.00%	100.00%
Line of credit loans
Loan Security
Total loans outstanding	1,305,851	1,385,228
Line of credit loans | Secured
Loan Security
Total loans outstanding	250,098	294,575
Loans receivable as a percentage of total loan	19.00%	21.00%
Line of credit loans | Unsecured
Loan Security
Total loans outstanding	$ 1,055,753	$ 1,090,653
Loans receivable as a percentage of total loan	81.00%	79.00%