Loans and Commitments (Details 9) (USD $) In Thousands, unless otherwise specified	3 Months Ended
	Aug. 31, 2014		Aug. 31, 2013		May 31, 2014
Activity in the loan loss allowance
Balance at the beginning of the period	$ 56,429		$ 54,325
(Recovery of) provision for loan losses	(6,771)		1,278
Recoveries of loans previously charged-off	53		53
Balance at the end of the period	49,711		55,656
Ending balance of the allowance:
Collectively evaluated	49,079				56,003
Individually evaluated	632				426
Total ending balance of the allowance	49,711		55,656
Recorded investment in loans:
Collectively evaluated	20,465,262				20,457,246
Individually evaluated	9,609				9,679
Total recorded investment in loans	20,474,871	[1],[2]	20,405,091		20,466,925	[1],[2]
Loans to members, net	20,425,160	[3]			20,410,496	[3]
Deferred origination costs	9,707	[1]	9,702		9,717	[1]
CFC
Activity in the loan loss allowance
Balance at the beginning of the period	45,600		41,246
(Recovery of) provision for loan losses	(5,192)		2,037
Recoveries of loans previously charged-off	53		53
Balance at the end of the period	40,461		43,336
Ending balance of the allowance:
Collectively evaluated	40,461				45,600
Individually evaluated					0
Total ending balance of the allowance	40,461		43,336
Recorded investment in loans:
Collectively evaluated	19,391,933				19,181,846
Individually evaluated	7,584				7,584
Total recorded investment in loans	19,399,517	[1]			19,189,430	[1]
Loans to members, net	19,359,056	[3]			19,143,830	[3]
RTFC
Activity in the loan loss allowance
Balance at the beginning of the period	4,282	[4]	9,158	[4]
(Recovery of) provision for loan losses	6	[4]	(661)	[4]
Balance at the end of the period	4,288	[4]	8,497	[4]
Ending balance of the allowance:
Collectively evaluated	3,656				3,876
Individually evaluated	632				406
Total ending balance of the allowance	4,288	[4]	8,497	[4]
Recorded investment in loans:
Collectively evaluated	435,157				447,851
Individually evaluated	1,695				1,695
Total recorded investment in loans	436,852	[1]			449,546	[1]
Loans to members, net	432,564	[3]			445,264	[3]
NCSC
Activity in the loan loss allowance
Balance at the beginning of the period	6,547	[4]	3,921	[4]
(Recovery of) provision for loan losses	(1,585)	[4]	(98)	[4]
Balance at the end of the period	4,962	[4]	3,823	[4]
Ending balance of the allowance:
Collectively evaluated	4,962				6,527
Individually evaluated	0				20
Total ending balance of the allowance	4,962	[4]	3,823	[4]
Recorded investment in loans:
Collectively evaluated	638,172				827,549
Individually evaluated	330				400
Total recorded investment in loans	638,502	[1]			827,949	[1]
Loans to members, net	$ 633,540	[3]			$ 821,402	[3]

[1] Includes nonperforming and restructured loans.

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

[3] Excludes deferred origination costs of $10 million as of August 31, 2014 and May 31, 2014.

[4] The allowance for loan losses recorded for RTFC and NCSC are held at CFC.