Segment Information (Details) - USD ($) $ in Thousands	3 Months Ended			9 Months Ended
	Feb. 29, 2016		Feb. 28, 2015	Feb. 29, 2016		Feb. 28, 2015	Nov. 30, 2015	May. 31, 2015		Nov. 30, 2014	May. 31, 2014
Segment Information
Losses on early extinguishment of debt	$ (333)		$ (703)	$ (333)		$ (703)
Statement of operations:
Interest income	253,633		238,740	756,074		711,266
Interest expense	(171,189)		(156,850)	(504,013)		(471,677)
Net interest income	82,444		81,890	252,061		239,589
Provision for loan losses	1,735		(2,304)	(4,067)		3,475
Net interest income after provision for loan losses	84,179		79,586	247,994		243,064
Non-interest income:
Fee and other income	5,604		5,020	17,336		19,249
Derivative losses	(243,036)		(98,770)	(356,237)		(223,209)
Results of operations from foreclosed assets	1,472		(1,369)	1,605		(33,059)
Total non-interest income	(235,960)		(95,119)	(337,296)		(237,019)
Non-interest expense:
General and administrative expenses	(22,352)		(18,008)	(65,418)		(54,788)
Loss Contingency Accrual, Provision			703
Other	(509)		(7)	(875)		50
Total non-interest expense	(23,194)		(18,718)	(66,626)		(55,441)
Income (loss) before income taxes	(174,975)		(34,251)	(155,928)		(49,396)
Income tax benefit (expense)	593		55	153		(100)
Net loss	(174,382)		(34,196)	(155,775)		(49,496)
Assets:
Total loans outstanding	23,134,215	[1],[2]	21,202,399	23,134,215	[1],[2]	21,202,399		$ 21,459,220	[1],[2]
Deferred origination costs	9,884	[1]	9,693	9,884	[1]	9,693		9,797	[1]
Less: Allowance for loan losses	(37,918)		(53,114)	(37,918)		(53,114)	$ (39,600)	(33,690)		$ (50,757)	$ (56,429)
Loans to members, net	23,106,181		21,158,978	23,106,181		21,158,978		21,435,327
Other assets	1,286,844		1,489,943	1,286,844		1,489,943
Total assets	24,393,025		22,648,921	24,393,025		22,648,921		$ 22,846,059
CFC
Segment Information
Losses on early extinguishment of debt	(333)			(333)		(703)
Statement of operations:
Interest income	250,814		235,616	747,490		701,924
Interest expense	(170,872)		(156,489)	(503,061)		(470,635)
Net interest income	79,942		79,127	244,429		231,289
Provision for loan losses	1,735		(2,304)	(4,067)		3,475
Net interest income after provision for loan losses	81,677		76,823	240,362		234,764
Non-interest income:
Fee and other income	5,341		4,928	16,020		18,800
Derivative losses	(240,363)		(97,424)	(352,153)		(219,656)
Results of operations from foreclosed assets	1,472		(1,369)	1,605		(33,059)
Total non-interest income	(233,550)		(93,865)	(334,528)		(233,915)
Non-interest expense:
General and administrative expenses	(20,266)		(16,227)	(58,419)		(49,479)
Loss Contingency Accrual, Provision			703
Other	(509)		(7)	(875)		50
Total non-interest expense	(21,108)		(16,937)	(59,627)		(50,132)
Income (loss) before income taxes	(172,981)		(33,979)	(153,793)		(49,283)
Net loss	(172,981)		(33,979)	(153,793)		(49,283)
Assets:
Total loans outstanding	23,095,053		21,187,603	23,095,053		21,187,603
Deferred origination costs	9,884		9,693	9,884		9,693
Less: Allowance for loan losses	(37,918)		(53,114)	(37,918)		(53,114)
Loans to members, net	23,067,019		21,144,182	23,067,019		21,144,182
Other assets	1,270,625		1,448,655	1,270,625		1,448,655
Total assets	24,337,644		22,592,837	24,337,644		22,592,837
Other
Statement of operations:
Interest income	11,367		11,791	34,693		34,926
Interest expense	(8,865)		(9,028)	(27,061)		(26,626)
Net interest income	2,502		2,763	7,632		8,300
Net interest income after provision for loan losses	2,502		2,763	7,632		8,300
Non-interest income:
Fee and other income	984		922	3,898		2,653
Derivative losses	(2,673)		(1,346)	(4,084)		(3,553)
Total non-interest income	(1,689)		(424)	(186)		(900)
Non-interest expense:
General and administrative expenses	(2,341)		(2,024)	(7,762)		(6,039)
Other	(466)		(587)	(1,819)		(1,474)
Total non-interest expense	(2,807)		(2,611)	(9,581)		(7,513)
Income (loss) before income taxes	(1,994)		(272)	(2,135)		(113)
Income tax benefit (expense)	593		55	153		(100)
Net loss	(1,401)		(217)	(1,982)		(213)
Assets:
Total loans outstanding	1,055,203		1,117,252	1,055,203		1,117,252
Loans to members, net	1,055,203		1,117,252	1,055,203		1,117,252
Other assets	120,001		157,122	120,001		157,122
Total assets	1,175,204		1,274,374	1,175,204		1,274,374
Elimination
Statement of operations:
Interest income	(8,548)		(8,667)	(26,109)		(25,584)
Interest expense	8,548		8,667	26,109		25,584
Non-interest income:
Fee and other income	(721)		(830)	(2,582)		(2,204)
Derivative losses	0		0	0		0
Total non-interest income	(721)		(830)	(2,582)		(2,204)
Non-interest expense:
General and administrative expenses	255		243	763		730
Other	466		587	1,819		1,474
Total non-interest expense	721		830	2,582		2,204
Assets:
Total loans outstanding	(1,016,041)		(1,102,456)	(1,016,041)		(1,102,456)
Loans to members, net	(1,016,041)		(1,102,456)	(1,016,041)		(1,102,456)
Other assets	(103,782)		(115,834)	(103,782)		(115,834)
Total assets	$ (1,119,823)		$ (1,218,290)	$ (1,119,823)		$ (1,218,290)

[1] Includes nonperforming and restructured loans.

[2] Represents the unpaid principal balance excluding deferred loan origination costs.