Guarantees (Details) (USD $)			3 Months Ended
	Aug. 31, 2014	May 31, 2014	Aug. 31, 2014 Long-term variable-rate bonds	Aug. 31, 2014 CFC	May 31, 2014 CFC	Aug. 31, 2014 CFC Distribution	May 31, 2014 CFC Distribution	Aug. 31, 2014 CFC Power supply	May 31, 2014 CFC Power supply	Aug. 31, 2014 CFC Statewide and associate	May 31, 2014 CFC Statewide and associate	Aug. 31, 2014 RTFC	May 31, 2014 RTFC	Aug. 31, 2014 NCSC	May 31, 2014 NCSC	Aug. 31, 2014 Financial guarantees Long-term tax-exempt bonds	May 31, 2014 Financial guarantees Long-term tax-exempt bonds	Aug. 31, 2014 Financial guarantees Long-term fixed-rate bonds	Aug. 31, 2014 Financial guarantees Long-term variable-rate bonds	May 31, 2014 Financial guarantees Long-term variable-rate bonds	Aug. 31, 2014 Letters of credit Master letter of credit	Aug. 31, 2014 Letters of credit	May 31, 2014 Letters of credit	Aug. 31, 2014 Letters of credit Letters of credit, secured	Aug. 31, 2014 Letters of credit Hybrid letter of credit	Aug. 31, 2014 Letters of credit Hybrid letter of credit facility subject to material adverse change clauses	Aug. 31, 2014 Letters of credit Adjustable and floating-rate tax-exempt bonds	May 31, 2014 Letters of credit Adjustable and floating-rate tax-exempt bonds	Aug. 31, 2014 Other guarantees	May 31, 2014 Other guarantees
Guarantees
Total	$ 981,540,000	$ 1,064,822,000		$ 925,922,000	$ 997,187,000	$ 162,585,000	$ 165,559,000	$ 757,996,000	$ 826,231,000	$ 5,341,000	$ 5,397,000	$ 2,303,000	$ 2,304,000	$ 53,315,000	$ 65,331,000	$ 516,745,000	$ 518,360,000	$ 73,000,000	$ 444,000,000	$ 445,000,000		$ 349,983,000	$ 431,064,000				$ 76,000,000	$ 125,000,000	$ 114,812,000	$ 115,398,000
Maximum potential exposure																		104,000,000											115,000,000
Amount of guarantee secured																								74,000,000
Maximum additional amount potentially required to be issued																					93,000,000
Commitments that may be used for the issuance of letters of credit or line of credit loan advances																									1,760,000,000	468,000,000
Commitment remaining under letter of credit facility																									1,292,000,000
Amount of unsecured guarantees	390,000,000	418,000,000
Unsecured guarantees as a percentage of total guarantees (percent)	40.00%	39.00%
Value of bonds issued under liquidity provider obligations			$ 520,000,000