Loans and Commitments (Details 5) (USD $) In Thousands, unless otherwise specified	3 Months Ended			9 Months Ended
	Feb. 28, 2014		Feb. 28, 2013	Feb. 28, 2014		Feb. 28, 2013	May 31, 2013
Activity in the loan loss allowance
Balance at the beginning of the period	$ 55,199		$ 148,737	$ 54,325		$ 143,326
Provision for (recovery of) loan losses	787		(378)	3,161		4,927
Charge-offs	0			(1,606)
Recoveries of loans previously charged-off	54		52	160		158
Balance at the end of the period	56,040		148,411	56,040		148,411
Ending balance of the allowance:
Collectively evaluated	55,526			55,526			50,898
Individually evaluated	514			514			3,427
Total ending balance of the allowance	56,040		148,411	56,040		148,411
Recorded investment in loans:
Collectively evaluated	20,616,904			20,616,904			20,233,867
Individually evaluated	18,429			18,429			62,450
Total recorded investment in loans	20,635,333	[1],[2]	19,477,734	20,635,333	[1],[2]	19,477,734	20,296,317	[1],[2]
Loans to members, net	20,579,293	[1]		20,579,293	[1]		20,241,992	[1]
RTFC
Activity in the loan loss allowance
Balance at the beginning of the period	7,859		8,314	9,158		8,562
Provision for (recovery of) loan losses	(2,450)		(214)	(2,143)		(462)
Charge-offs	0			(1,606)
Recoveries of loans previously charged-off	0		0	0		0
Balance at the end of the period	5,409		8,100	5,409		8,100
Ending balance of the allowance:
Collectively evaluated	4,950			4,950			5,731
Individually evaluated	459			459			3,427
Total ending balance of the allowance	5,409		8,100	5,409		8,100
Recorded investment in loans:
Collectively evaluated	450,097			450,097			492,862
Individually evaluated	5,395			5,395			10,497
Total recorded investment in loans	455,492	[1]		455,492	[1]		503,359	[1]
Loans to members, net	450,083	[1]		450,083	[1]		494,201	[1]
NCSC
Activity in the loan loss allowance
Balance at the beginning of the period	4,578		6,845	3,921		7,823
Provision for (recovery of) loan losses	1,694		(596)	2,351		(1,574)
Charge-offs	0			0
Recoveries of loans previously charged-off	0		0	0		0
Balance at the end of the period	6,272		6,249	6,272		6,249
Ending balance of the allowance:
Collectively evaluated	6,217			6,217			3,921
Individually evaluated	55			55			0
Total ending balance of the allowance	6,272		6,249	6,272		6,249
Recorded investment in loans:
Collectively evaluated	778,845			778,845			773,141
Individually evaluated	450			450			0
Total recorded investment in loans	779,295	[1]		779,295	[1]		773,141	[1]
Loans to members, net	773,023	[1]		773,023	[1]		769,220	[1]
CFC
Activity in the loan loss allowance
Balance at the beginning of the period	42,762		133,578	41,246		126,941
Provision for (recovery of) loan losses	787		(378)	3,161		4,927
Charge-offs	0			0
Recoveries of loans previously charged-off	54		52	160		158
Balance at the end of the period	44,359		134,062	44,359		134,062
Ending balance of the allowance:
Collectively evaluated	44,359			44,359			41,246
Individually evaluated	0			0			0
Total ending balance of the allowance	44,359		134,062	44,359		134,062
Recorded investment in loans:
Collectively evaluated	19,387,962			19,387,962			18,967,864
Individually evaluated	12,584			12,584			51,953
Total recorded investment in loans	19,400,546	[1],[2]	19,445,360	19,400,546	[1],[2]	19,445,360	19,019,817	[1],[2]
Loans to members, net	$ 19,356,187	[1]		$ 19,356,187	[1]		$ 18,978,571	[1]

[1] Excludes deferred origination costs of $10 million at February 28, 2014 and May 31, 2013.

[2] Includes nonperforming and restructured loans.