Fair Value Disclosures - Unobservable Input Reconciliation (Details) - Fair Value, Inputs, Level 3 [Member] - Fair Value, Measurements, Recurring [Member] - USD ($) $ in Thousands		3 Months Ended				9 Months Ended
		Sep. 30, 2015		Sep. 30, 2014		Sep. 30, 2015		Sep. 30, 2014
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning Balance		$ 5,951,172		$ 5,176,636		$ 5,472,078		$ 6,770,031
Purchases		291,374		392,975		968,668		1,017,519
Sales		0		(14,550)		0		(26,675)
Settlements		(115,090)		(428,864)		(329,042)		(1,094,797)
Realized and Unrealized Gains/(Losses) included in Income		15,727		(3,031)		13,780		3,745
Unrealized Gains/(Losses) included in Other Comprehen-sive Income		(54,681)		6,192		(36,982)		71,621
Transfers Out								(1,612,086)
Ending Balance		6,088,502		5,129,358		6,088,502		5,129,358
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning Balance								(235)
Purchases								0
Sales								0
Settlements								0
Realized and Unrealized Gains/(Losses) included in Income								235
Unrealized Gains/(Losses) included in Other Comprehen-sive Income								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		40,788		56,051		41,265		66,418
Purchases		0		0		0		0
Sales		0		(14,550)		0		(26,675)
Settlements		(106)		(134)		(543)		(559)
Realized and Unrealized Gains/(Losses) included in Income		(50)		(426)		304		(435)
Unrealized Gains/(Losses) included in Other Comprehen-sive Income		4,842		797		4,448		2,989
Transfers Out								0
Ending Balance		45,474		41,738		45,474		41,738
USDA Securities [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Trading Securities, Unrealized Holding Loss		100
Trading Securities, Unrealized Gains				0		200		700
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning Balance		1,859,176		1,683,029		1,771,532		1,612,013
Purchases		91,374		97,275		291,981		256,044
Sales		0		0		0		0
Settlements		(53,059)		(45,900)		(193,159)		(178,458)
Realized and Unrealized Gains/(Losses) included in Income		(57)		(56)		120		161
Unrealized Gains/(Losses) included in Other Comprehen-sive Income		(11,076)		(3,503)		15,884		41,085
Transfers Out								0
Ending Balance		1,886,358		1,730,845		1,886,358		1,730,845
Available-for-sale Securities [Member] | Investment Securities [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning Balance		40,182		55,171		40,576		65,490
Purchases		0		0		0		0
Sales		0		(14,550)		0		(26,675)
Settlements		0		(7)		0		(18)
Realized and Unrealized Gains/(Losses) included in Income		(100)		(450)		(100)		(825)
Unrealized Gains/(Losses) included in Other Comprehen-sive Income		4,842		797		4,448		2,989
Transfers Out								0
Ending Balance		44,924		40,961		44,924		40,961
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		4,051,208		3,437,556		3,659,281		5,091,600
Purchases		200,000		295,700		676,687		761,475
Sales		0		0		0		0
Settlements		(61,925)		(382,830)		(135,340)		(915,780)
Realized and Unrealized Gains/(Losses) included in Income		15,834		(2,549)		13,356		4,019
Unrealized Gains/(Losses) included in Other Comprehen-sive Income		(48,447)		8,898		(57,314)		27,547
Transfers Out								(1,612,086)
Ending Balance		4,156,670		3,356,775		4,156,670		3,356,775
Available-for-sale Securities [Member] | USDA Securities [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning Balance		1,825,406		1,636,930		1,731,222		1,553,669
Purchases		91,374		97,275		291,981		256,044
Sales		0		0		0		0
Settlements		(51,282)		(42,821)		(184,665)		(162,917)
Realized and Unrealized Gains/(Losses) included in Income		0		0		0		0
Unrealized Gains/(Losses) included in Other Comprehen-sive Income		(11,076)		(3,503)		15,884		41,085
Transfers Out								0
Ending Balance		1,854,422		1,687,881		1,854,422		1,687,881
Trading Securities [Member] | Investment Securities [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning Balance		606		880		689		928
Purchases		0		0		0		0
Sales		0		0		0		0
Settlements		(106)		(127)		(543)		(541)
Realized and Unrealized Gains/(Losses) included in Income		50		24		404		390
Unrealized Gains/(Losses) included in Other Comprehen-sive Income		0		0		0		0
Transfers Out								0
Ending Balance		550		777		550		777
Trading Securities [Member] | USDA Securities [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning Balance		33,770		46,099	[1]	40,310	[2]	58,344	[3]
Purchases		0		0	[1]	0	[2]	0	[3]
Sales		0		0	[1]	0	[2]	0	[3]
Settlements		(1,777)		(3,079)	[1]	(8,494)	[2]	(15,541)	[3]
Realized and Unrealized Gains/(Losses) included in Income		(57)		(56)	[1]	120	[2]	161	[3]
Unrealized Gains/(Losses) included in Other Comprehen-sive Income		0		0	[1]	0	[2]	0	[3]
Transfers Out	[3]							0
Ending Balance		31,936	[2]	42,964	[1],[3]	31,936	[2]	42,964	[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		4,016,200	[4]	3,416,512		3,631,662	[4]	5,070,366
Purchases		200,000	[4]	295,700		664,175	[4]	761,475
Sales		0	[4]	0		0	[4]	0
Settlements		(59,311)	[4]	(382,630)		(126,308)	[4]	(915,218)
Realized and Unrealized Gains/(Losses) included in Income		15,834	[4]	(2,549)		13,356	[4]	4,019
Unrealized Gains/(Losses) included in Other Comprehen-sive Income		(46,761)	[4]	9,293		(56,923)	[4]	27,770
Transfers Out				(1,600,000)		0		(1,612,086)
Ending Balance		4,125,962	[4]	3,336,326		4,125,962	[4]	3,336,326
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		35,008		21,044		27,619		21,234
Purchases		0		0		12,512		0
Sales		0		0		0		0
Settlements		(2,614)		(200)		(9,032)		(562)
Realized and Unrealized Gains/(Losses) included in Income		0		0		0		0
Unrealized Gains/(Losses) included in Other Comprehen-sive Income		(1,686)		(395)		(391)		(223)
Transfers Out								0
Ending Balance		30,708		20,449		30,708		20,449
Derivative Financial Instruments, Liabilities [Member]
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning Balance								(235)
Purchases								0
Sales								0
Settlements								0
Realized and Unrealized Gains/(Losses) included in Income								235
Unrealized Gains/(Losses) included in Other Comprehen-sive Income								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		40,182		54,976		40,576		65,285
Purchases		0		0		0		0
Sales		0		(14,550)		0		(26,675)
Settlements		0		0		0		0
Realized and Unrealized Gains/(Losses) included in Income		(100)		(450)		(100)		(825)
Unrealized Gains/(Losses) included in Other Comprehen-sive Income		4,842		798		4,448		2,989
Transfers Out								0
Ending Balance		44,924		40,774		44,924		40,774
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				195				205
Purchases				0				0
Sales				0				0
Settlements				(7)				(18)
Realized and Unrealized Gains/(Losses) included in Income				0				0
Unrealized Gains/(Losses) included in Other Comprehen-sive Income				(1)				0
Transfers Out								0
Ending Balance				187				187
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		606	[5]	880	[6]	689	[7]	928	[8]
Purchases		0	[5]	0	[6]	0	[7]	0	[8]
Sales		0	[5]	0	[6]	0	[7]	0	[8]
Settlements		(106)	[5]	(127)	[6]	(543)	[7]	(541)	[8]
Realized and Unrealized Gains/(Losses) included in Income		50	[5]	24	[6]	404	[7]	390	[8]
Unrealized Gains/(Losses) included in Other Comprehen-sive Income		0	[5]	0	[6]	0	[7]	0	[8]
Transfers Out	[8]							0
Ending Balance		$ 550	[5],[7]	$ 777	[6],[8]	$ 550	[5],[7]	$ 777	[6],[8]

[1] Includes immaterial unrealized losses attributable to assets still held as of September 30, 2014 that are recorded in "(Losses)/gains on trading securities."

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

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

[4] Includes unrealized losses of $0.1 million attributable to assets still held as of September 30, 2015 that are recorded in "(Losses)/gains on trading securities."

[5] Unrealized gains are attributable to assets still held as of September 30, 2015 and are recorded in "(Losses)/gains on trading securities."

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

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

[8] Unrealized gains are attributable to assets still held as of September 30, 2014 and are recorded in "(Losses)/gains on trading securities."