Fair Value Disclosures - Unobservable Input Reconciliation (Details) (Fair Value, Inputs, Level 3 [Member], Fair Value, Measurements, Recurring [Member], USD $) In Thousands, unless otherwise specified	3 Months Ended				12 Months Ended
	Dec. 31, 2014		Mar. 31, 2014		Dec. 31, 2014		Dec. 31, 2013		Dec. 31, 2012
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning Balance			$ 6,770,031		$ 6,770,031		$ 6,421,447		$ 5,843,186
Purchases					1,434,461		1,635,627		1,469,057
Sales					26,675		0		5,327
Settlements					1,153,191		1,129,054		873,152
Realized and Unrealized Gains/(Losses) included in Income					15,292		(19,049)		6,695
Unrealized Gains/(Losses) included in Other Comprehen-sive Income					64,946		(138,940)		(19,012)
Transfers Out					1,632,786
Ending Balance	5,472,078				5,472,078		6,770,031		6,421,447
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning Balance			235		235		691		1,335
Purchases					0		0		0
Sales					0		0		0
Settlements					0		0		0
Realized and Unrealized Gains/(Losses) included in Income					235		456		644
Unrealized Gains/(Losses) included in Other Comprehen-sive Income					0		0		0
Transfers Out					0
Ending Balance	0				0		235		691
Investment Securities [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning Balance			66,418		66,418		64,406		62,009
Purchases					0		233		0
Sales					26,675		0		0
Settlements					890		798		812
Realized and Unrealized Gains/(Losses) included in Income					(379)		455		263
Unrealized Gains/(Losses) included in Other Comprehen-sive Income					2,791		2,122		2,946
Transfers Out					0
Ending Balance	41,265				41,265		66,418		64,406
USDA Securities [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Trading Securities, Unrealized Holding Loss							500
Trading Securities, Unrealized Gains					1,800				300
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning Balance			1,612,013		1,612,013		1,590,783		1,491,905
Purchases					335,359		361,894		479,324
Sales					0		0		0
Settlements					228,585		278,605		364,900
Realized and Unrealized Gains/(Losses) included in Income					1,151		(1,274)		44
Unrealized Gains/(Losses) included in Other Comprehen-sive Income					51,594		(60,785)		(15,590)
Transfers Out					0
Ending Balance	1,771,532				1,771,532		1,612,013		1,590,783
Available-for-sale Securities [Member] | Investment Securities [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning Balance			65,490		65,490		63,159		60,213
Purchases					0		233		0
Sales					26,675		0		0
Settlements					205		24		0
Realized and Unrealized Gains/(Losses) included in Income					(825)		0		0
Unrealized Gains/(Losses) included in Other Comprehen-sive Income					2,791		2,122		2,946
Transfers Out					0
Ending Balance	40,576				40,576		65,490		63,159
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			5,091,600		5,091,600		4,766,258		4,289,272
Purchases					1,099,102		1,273,500		989,733
Sales					0		0		5,327
Settlements					923,716		849,651		507,440
Realized and Unrealized Gains/(Losses) included in Income					14,520		(18,230)		6,388
Unrealized Gains/(Losses) included in Other Comprehen-sive Income					10,561		(80,277)		(6,368)
Transfers Out					1,632,786
Ending Balance	3,659,281				3,659,281		5,091,600		4,766,258
Available-for-sale Securities [Member] | USDA Securities [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning Balance			1,553,669		1,553,669		1,486,595		1,279,546
Purchases					335,359		361,894		479,324
Sales					0		0		0
Settlements					209,400		234,035		256,685
Realized and Unrealized Gains/(Losses) included in Income					0		0		0
Unrealized Gains/(Losses) included in Other Comprehen-sive Income					51,594		(60,785)		(15,590)
Transfers Out					0
Ending Balance	1,731,222				1,731,222		1,553,669		1,486,595
Trading Securities [Member] | Investment Securities [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning Balance			928		928		1,247		1,796
Purchases					0		0		0
Sales					0		0		0
Settlements					685		774		812
Realized and Unrealized Gains/(Losses) included in Income					446		455		263
Unrealized Gains/(Losses) included in Other Comprehen-sive Income					0		0		0
Transfers Out					0
Ending Balance	689				689		928		1,247
Trading Securities [Member] | USDA Securities [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning Balance			58,344	[1],[2]	58,344	[1],[2]	104,188	[1],[3]	212,359	[3]
Purchases					0	[2]	0	[1]	0	[3]
Sales					0	[2]	0	[1]	0	[3]
Settlements					19,185	[2]	44,570	[1]	108,215	[3]
Realized and Unrealized Gains/(Losses) included in Income					1,151	[2]	(1,274)	[1]	44	[3]
Unrealized Gains/(Losses) included in Other Comprehen-sive Income					0	[2]	0	[1]	0	[3]
Transfers Out					0	[2]
Ending Balance	40,310	[2]			40,310	[2]	58,344	[1],[2]	104,188	[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			5,070,366	[4]	5,070,366	[4]	4,739,577		4,253,673
Purchases					1,091,475	[4]	1,273,500		984,406
Sales					0	[4]	0		0
Settlements					922,908	[4]	844,437		498,533
Realized and Unrealized Gains/(Losses) included in Income					14,520	[4]	(18,230)		6,388
Unrealized Gains/(Losses) included in Other Comprehen-sive Income					10,995	[4]	(80,044)		(6,357)
Transfers Out	20,700		1,600,000		1,632,786	[4]	0		0
Ending Balance	3,631,662	[4]			3,631,662	[4]	5,070,366	[4]	4,739,577
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			21,234		21,234		26,681		35,599
Purchases					7,627		0		5,327
Sales					0		0		5,327
Settlements					808		5,214		8,907
Realized and Unrealized Gains/(Losses) included in Income					0		0		0
Unrealized Gains/(Losses) included in Other Comprehen-sive Income					(434)		(233)		(11)
Transfers Out					0
Ending Balance	27,619				27,619		21,234		26,681
Derivative Financial Instruments, Liabilities [Member]
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning Balance			235	[5]	235	[5]	691	[5],[6]	1,335	[6]
Purchases					0		0	[5]	0	[6]
Sales					0		0	[5]	0	[6]
Settlements					0		0	[5]	0	[6]
Realized and Unrealized Gains/(Losses) included in Income					235		456	[5]	644	[6]
Unrealized Gains/(Losses) included in Other Comprehen-sive Income					0		0	[5]	0	[6]
Transfers Out					0
Ending Balance	0				0		235	[5]	691	[5],[6]
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			65,285		65,285		63,159		60,213
Purchases					0		0		0
Sales					26,675		0		0
Settlements					0		0		0
Realized and Unrealized Gains/(Losses) included in Income					(825)		0		0
Unrealized Gains/(Losses) included in Other Comprehen-sive Income					2,791		2,126		2,946
Transfers Out					0
Ending Balance	40,576				40,576		65,285		63,159
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			205		205		0
Purchases					0		233
Sales					0		0
Settlements					205		24
Realized and Unrealized Gains/(Losses) included in Income					0		0
Unrealized Gains/(Losses) included in Other Comprehen-sive Income					0		(4)
Transfers Out					0
Ending Balance	0				0		205
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			928	[7],[8]	928	[7],[8]	1,247	[7],[9]	1,796	[9]
Purchases					0	[8]	0	[7]	0	[9]
Sales					0	[8]	0	[7]	0	[9]
Settlements					685	[8]	774	[7]	812	[9]
Realized and Unrealized Gains/(Losses) included in Income					446	[8]	455	[7]	263	[9]
Unrealized Gains/(Losses) included in Other Comprehen-sive Income					0	[8]	0	[7]	0	[9]
Transfers Out					0	[8]
Ending Balance	$ 689	[8]			$ 689	[8]	$ 928	[7],[8]	$ 1,247	[7],[9]

[1] Includes unrealized losses of $0.5 million attributable to assets still held as of December 31, 2013 that are recorded in "Gains/(losses) on trading securities."

[2] Includes unrealized gains of $1.8 million attributable to assets still held as of December 31, 2014 that are recorded in "Gains/(losses) on trading securities."

[3] Includes unrealized gains of $0.3 million attributable to assets still held as of December 31, 2012 that are recorded in "Gains/(losses) on trading securities."

[4] Includes $1.6 billion of AgVantage Securities transferred from available-for-sale to held-to-maturity on January 1, 2014 and $20.7 million of AgVantage securities purchased during 2014 transferred from available-for-sale to held-to-maturity.

[5] Unrealized gains are attributable to liabilities still held as of December 31, 2013 and are recorded in "(Losses)/gains on financial derivatives and hedging activities."

[6] Unrealized gains are attributable to liabilities still held as of December 31, 2012 and are recorded in "(Losses)/gains on financial derivatives and hedging activities."

[7] (1)Unrealized gains are attributable to assets still held as of December 31, 2013 and are recorded in "Gains/(losses) on trading securities."

[8] Unrealized gains are attributable to assets still held as of December 31, 2014 and are recorded in "Gains/(losses) on trading securities."

[9] Unrealized gains are attributable to assets still held as of December 31, 2012 and are recorded in "Gains/(losses) on trading securities."