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
	Mar. 31, 2015		Mar. 31, 2014
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning Balance	$ 5,472,078		$ 6,770,031
Purchases	304,101		237,984
Sales	0		0
Settlements	129,726		244,801
Realized and Unrealized Gains/(Losses) included in Income	9,239		3,405
Unrealized Gains/(Losses) included in Other Comprehen-sive Income	59,971		52,580
Transfers Out	0		(1,612,086)
Ending Balance	5,715,663		5,207,113
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			74
Unrealized Gains/(Losses) included in Other Comprehen-sive Income			0
Transfers Out			0
Ending Balance			161
Investment Securities [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning Balance	41,265		66,418
Purchases	0		0
Sales	0		0
Settlements	247		287
Realized and Unrealized Gains/(Losses) included in Income	196		278
Unrealized Gains/(Losses) included in Other Comprehen-sive Income	(197)		(320)
Transfers Out	0		0
Ending Balance	41,017		66,089
USDA Securities [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Trading Securities, Unrealized Holding Loss			700
Trading Securities, Unrealized Gains	200
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning Balance	1,771,532		1,612,013
Purchases	89,186		67,984
Sales	0		0
Settlements	67,074		68,074
Realized and Unrealized Gains/(Losses) included in Income	166		377
Unrealized Gains/(Losses) included in Other Comprehen-sive Income	38,627		39,461
Transfers Out	0		0
Ending Balance	1,832,437		1,651,761
Available-for-sale Securities [Member] | Investment Securities [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning Balance	40,576		65,490
Purchases	0		0
Sales	0		0
Settlements	0		4
Realized and Unrealized Gains/(Losses) included in Income	0		0
Unrealized Gains/(Losses) included in Other Comprehen-sive Income	(197)		(320)
Transfers Out	0		0
Ending Balance	40,379		65,166
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	3,659,281		5,091,600
Purchases	214,915		170,000
Sales	0		0
Settlements	62,405		176,440
Realized and Unrealized Gains/(Losses) included in Income	8,877		2,750
Unrealized Gains/(Losses) included in Other Comprehen-sive Income	21,541		13,439
Transfers Out	0
Ending Balance	3,842,209		3,489,263
Available-for-sale Securities [Member] | USDA Securities [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning Balance	1,731,222		1,553,669
Purchases	89,186		67,984
Sales	0		0
Settlements	64,191		60,455
Realized and Unrealized Gains/(Losses) included in Income	0		0
Unrealized Gains/(Losses) included in Other Comprehen-sive Income	38,627		39,461
Transfers Out	0		0
Ending Balance	1,794,844		1,600,659
Trading Securities [Member] | Investment Securities [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning Balance	689		928
Purchases	0		0
Sales	0		0
Settlements	247		283
Realized and Unrealized Gains/(Losses) included in Income	196		278
Unrealized Gains/(Losses) included in Other Comprehen-sive Income	0		0
Transfers Out	0		0
Ending Balance	638		923
Trading Securities [Member] | USDA Securities [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning Balance	40,310		58,344	[1]
Purchases	0		0	[1]
Sales	0		0	[1]
Settlements	2,883		7,619	[1]
Realized and Unrealized Gains/(Losses) included in Income	166		377	[1]
Unrealized Gains/(Losses) included in Other Comprehen-sive Income	0		0	[1]
Transfers Out	0		0
Ending Balance	37,593		51,102	[1]
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	3,631,662	[2]	5,070,366
Purchases	214,915	[2]	170,000
Sales	0	[2]	0
Settlements	57,753	[2]	176,269
Realized and Unrealized Gains/(Losses) included in Income	8,877	[2]	2,750
Unrealized Gains/(Losses) included in Other Comprehen-sive Income	21,003	[2]	12,894
Transfers Out	0	[2]	(1,612,086)	[2]
Ending Balance	3,818,704	[2]	3,467,655
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	27,619		21,234
Purchases	0		0
Sales	0		0
Settlements	4,652		171
Realized and Unrealized Gains/(Losses) included in Income	0		0
Unrealized Gains/(Losses) included in Other Comprehen-sive Income	538		545
Transfers Out	0		0
Ending Balance	23,505		21,608
Derivative Financial Instruments, Liabilities [Member]
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning Balance			235	[3]
Purchases			0	[3]
Sales			0	[3]
Settlements			0	[3]
Realized and Unrealized Gains/(Losses) included in Income			74	[3]
Unrealized Gains/(Losses) included in Other Comprehen-sive Income			0	[3]
Transfers Out			0
Ending Balance			161	[3]
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	40,576		65,285
Purchases	0		0
Sales	0		0
Settlements	0		0
Realized and Unrealized Gains/(Losses) included in Income	0		0
Unrealized Gains/(Losses) included in Other Comprehen-sive Income	(197)		(322)
Transfers Out	0		0
Ending Balance	40,379		64,963
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
Purchases			0
Sales			0
Settlements			4
Realized and Unrealized Gains/(Losses) included in Income			0
Unrealized Gains/(Losses) included in Other Comprehen-sive Income			2
Transfers Out			0
Ending Balance			203
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	689	[4]	928	[5]
Purchases	0	[4]	0	[5]
Sales	0	[4]	0	[5]
Settlements	247	[4]	283	[5]
Realized and Unrealized Gains/(Losses) included in Income	196	[4]	278	[5]
Unrealized Gains/(Losses) included in Other Comprehen-sive Income	0	[4]	0	[5]
Transfers Out	0	[4]	0	[4]
Ending Balance	$ 638	[4]	$ 923	[5]

[1] Includes unrealized losses of $0.7 million attributable to assets still held as of March 31, 2014 that are recorded in "Gains on trading securities."

[2] Includes unrealized gains of $0.2 million attributable to assets still held as of March 31, 2015 that are recorded in "Gains on trading securities."

[3] Unrealized gains are attributable to liabilities still held as of March 31, 2014 and are recorded in "Losses on financial derivatives and hedging activities."

[4] Unrealized gains are attributable to assets still held as of March 31, 2015 and are recorded in "Gains on trading securities."

[5] (1) Unrealized gains are attributable to assets still held as of March 31, 2014 and are recorded in "Gains on trading securities."