Fair Value Disclosures - Unobservable Input Reconciliation (Details) - Fair Value, Inputs, Level 3 [Member] - Fair Value, Measurements, Recurring [Member] - USD ($) $ in Thousands		3 Months Ended				6 Months Ended
		Jun. 30, 2015		Jun. 30, 2014		Jun. 30, 2015		Jun. 30, 2014
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning Balance		$ 5,715,663		$ 5,207,113		$ 5,472,078		$ 6,770,031
Purchases		373,193		386,560		677,294		624,544
Sales		0		(12,125)		0		(12,125)
Settlements		(84,227)		(421,131)		(213,952)		(665,932)
Realized and Unrealized Gains/(Losses) included in Income		(11,185)		3,371		(1,947)		6,776
Unrealized Gains/(Losses) included in Other Comprehen-sive Income		(42,272)		12,848		17,699		65,428
Transfers Out								(1,612,086)
Ending Balance		5,951,172		5,176,636		5,951,172		5,176,636
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning Balance				(161)				(235)
Purchases				0				0
Sales				0				0
Settlements				0				0
Realized and Unrealized Gains/(Losses) included in Income				161				235
Unrealized Gains/(Losses) included in Other Comprehen-sive Income				0				0
Transfers Out								0
Ending Balance				0				0
Investment Securities [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning Balance		41,017		66,089		41,265		66,418
Purchases		0		0		0		0
Sales		0		(12,125)		0		(12,125)
Settlements		(190)		(138)		(437)		(425)
Realized and Unrealized Gains/(Losses) included in Income		158		(287)		354		(9)
Unrealized Gains/(Losses) included in Other Comprehen-sive Income		(197)		2,512		(394)		2,192
Transfers Out								0
Ending Balance		40,788		56,051		40,788		56,051
USDA Securities [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Trading Securities, Unrealized Gains		100				200		700
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning Balance		1,832,437		1,651,761		1,771,532		1,612,013
Purchases		111,421		90,785		200,607		158,769
Sales		0		0		0		0
Settlements		(73,026)		(64,483)		(140,100)		(132,557)
Realized and Unrealized Gains/(Losses) included in Income		11		(160)		177		217
Unrealized Gains/(Losses) included in Other Comprehen-sive Income		(11,667)		5,126		26,960		44,587
Transfers Out								0
Ending Balance		1,859,176		1,683,029		1,859,176		1,683,029
Available-for-sale Securities [Member] | Investment Securities [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning Balance		40,379		65,166		40,576		65,490
Purchases		0		0		0		0
Sales		0		(12,125)		0		(12,125)
Settlements		0		(7)		0		(11)
Realized and Unrealized Gains/(Losses) included in Income		0		(375)		0		(375)
Unrealized Gains/(Losses) included in Other Comprehen-sive Income		(197)		2,512		(394)		2,192
Transfers Out								0
Ending Balance		40,182		55,171		40,182		55,171
Available-for-sale Securities [Member] | Farmer Mac Guaranteed Securities [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning Balance		3,842,209		3,489,263		3,659,281		5,091,600
Purchases		261,772		295,775		476,687		465,775
Sales		0		0		0		0
Settlements		(11,011)		(356,510)		(73,415)		(532,950)
Realized and Unrealized Gains/(Losses) included in Income		(11,354)		3,818		(2,478)		6,568
Unrealized Gains/(Losses) included in Other Comprehen-sive Income		(30,408)		5,210		(8,867)		18,649
Transfers Out								(1,612,086)
Ending Balance		4,051,208		3,437,556		4,051,208		3,437,556
Available-for-sale Securities [Member] | USDA Securities [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning Balance		1,794,844		1,600,659		1,731,222		1,553,669
Purchases		111,421		90,785		200,607		158,769
Sales		0		0		0		0
Settlements		(69,192)		(59,640)		(133,383)		(120,095)
Realized and Unrealized Gains/(Losses) included in Income		0		0		0		0
Unrealized Gains/(Losses) included in Other Comprehen-sive Income		(11,667)		5,126		26,960		44,587
Transfers Out								0
Ending Balance		1,825,406		1,636,930		1,825,406		1,636,930
Trading Securities [Member] | Investment Securities [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning Balance		638		923		689		928
Purchases		0		0		0		0
Sales		0		0		0		0
Settlements		(190)		(131)		(437)		(414)
Realized and Unrealized Gains/(Losses) included in Income		158		88		354		366
Unrealized Gains/(Losses) included in Other Comprehen-sive Income		0		0		0		0
Transfers Out								0
Ending Balance		606		880		606		880
Trading Securities [Member] | USDA Securities [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning Balance		37,593		51,102	[1]	40,310	[2]	58,344	[3]
Purchases		0		0	[1]	0	[2]	0	[3]
Sales		0		0	[1]	0	[2]	0	[3]
Settlements		(3,834)		(4,843)	[1]	(6,717)	[2]	(12,462)	[3]
Realized and Unrealized Gains/(Losses) included in Income		11		(160)	[1]	177	[2]	217	[3]
Unrealized Gains/(Losses) included in Other Comprehen-sive Income		0		0	[1]	0	[2]	0	[3]
Transfers Out	[3]							0
Ending Balance		33,770	[2]	46,099	[1],[3]	33,770	[2]	46,099	[1],[3]
Institutional Credit [Member] | Available-for-sale Securities [Member] | Farmer Mac Guaranteed Securities [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning Balance		3,818,704	[4]	3,467,655		3,631,662	[4]	5,070,366
Purchases		249,260	[4]	295,775		464,175	[4]	465,775
Sales		0	[4]	0		0	[4]	0
Settlements		(9,245)	[4]	(356,319)		(66,997)	[4]	(532,588)
Realized and Unrealized Gains/(Losses) included in Income		(11,354)	[4]	3,818		(2,478)	[4]	6,568
Unrealized Gains/(Losses) included in Other Comprehen-sive Income		(31,165)	[4]	5,583		(10,162)	[4]	18,477
Transfers Out				(1,600,000)		0		(1,612,086)
Ending Balance		4,016,200	[4]	3,416,512		4,016,200	[4]	3,416,512
USDA Guarantees [Member] | Available-for-sale Securities [Member] | Farmer Mac Guaranteed Securities [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning Balance		23,505		21,608		27,619		21,234
Purchases		12,512		0		12,512		0
Sales		0		0		0		0
Settlements		(1,766)		(191)		(6,418)		(362)
Realized and Unrealized Gains/(Losses) included in Income		0		0		0		0
Unrealized Gains/(Losses) included in Other Comprehen-sive Income		757		(373)		1,295		172
Transfers Out								0
Ending Balance		35,008		21,044		35,008		21,044
Derivative Financial Instruments, Liabilities [Member]
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning Balance				(161)				(235)
Purchases				0				0
Sales				0				0
Settlements				0				0
Realized and Unrealized Gains/(Losses) included in Income				161				235
Unrealized Gains/(Losses) included in Other Comprehen-sive Income				0				0
Ending Balance				0				0
Floating Interest Rate [Member] | Available-for-sale Securities [Member] | Floating rate auction-rate certificates backed by Government guaranteed student loans
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning Balance		40,379		64,963		40,576		65,285
Purchases		0		0		0		0
Sales		0		(12,125)		0		(12,125)
Settlements		0		0		0		0
Realized and Unrealized Gains/(Losses) included in Income		0		(375)		0		(375)
Unrealized Gains/(Losses) included in Other Comprehen-sive Income		(197)		2,513		(394)		2,191
Transfers Out								0
Ending Balance		40,182		54,976		40,182		54,976
Floating Interest Rate [Member] | Available-for-sale Securities [Member] | Government/GSE Guaranteed Mortgage Backed Securities [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning Balance				203				205
Purchases				0				0
Sales				0				0
Settlements				(7)				(11)
Realized and Unrealized Gains/(Losses) included in Income				0				0
Unrealized Gains/(Losses) included in Other Comprehen-sive Income				(1)				1
Transfers Out								0
Ending Balance				195				195
Floating Interest Rate [Member] | Trading Securities [Member] | Asset-backed Securities [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning Balance		638	[5]	923	[6]	689	[7]	928	[8]
Purchases		0	[5]	0	[6]	0	[7]	0	[8]
Sales		0	[5]	0	[6]	0	[7]	0	[8]
Settlements		(190)	[5]	(131)	[6]	(437)	[7]	(414)	[8]
Realized and Unrealized Gains/(Losses) included in Income		158	[5]	88	[6]	354	[7]	366	[8]
Unrealized Gains/(Losses) included in Other Comprehen-sive Income		0	[5]	0	[6]	0	[7]	0	[8]
Transfers Out	[8]							0
Ending Balance		$ 606	[5],[7]	$ 880	[6],[8]	$ 606	[5],[7]	$ 880	[6],[8]

[1] Includes immaterial unrealized losses attributable to assets still held as of June 30, 2014 that are recorded in "Gains on trading securities."

[2] Includes unrealized gains of $0.2 million attributable to assets still held as of June 30, 2015 that are recorded in "Gains on trading securities."

[3] Includes unrealized gains of $0.7 million attributable to assets still held as of June 30, 2014 that are recorded in "Gains on trading securities."

[4] Includes unrealized gains of $0.1 million attributable to assets still held as of June 30, 2015 that are recorded in "Gains on trading securities."

[5] Unrealized gains are attributable to assets still held as of June 30, 2015 and are recorded in "Gains on trading securities."

[6] (1) Unrealized gains are attributable to assets still held as of June 30, 2014 and are recorded in "Gains on trading securities."

[7] (1)Unrealized gains are attributable to assets still held as of June 30, 2015 and are recorded in "Gains on trading securities."

[8] Unrealized gains are attributable to assets still held as of June 30, 2014 and are recorded in "Gains on trading securities."