Fair Value Disclosures - Unobservable Input Reconciliation (Details) - Fair Value, Inputs, Level 3 [Member] - Fair Value, Measurements, Recurring [Member] - USD ($)		3 Months Ended
		Mar. 31, 2017		Mar. 31, 2016
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning Balance		$ 4,891,803,000		$ 6,115,339,000
Transfers In		7,041,000
Purchases		572,116,000		1,014,505,000
Sales		(32,589,000)		(30,454,000)
Settlements		(163,723,000)		(599,792,000)
Realized and Unrealized Gains/(Losses) included in Income		(3,297,000)		24,661,000
Unrealized Gains/(Losses) included in Other Comprehen-sive Income		13,240,000		(5,759,000)
Ending Balance		5,284,591,000		6,518,500,000
Investment Securities [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning Balance				45,415,000
Purchases				0
Sales				(26,806,000)
Settlements				(206,000)
Realized and Unrealized Gains/(Losses) included in Income				104,000
Unrealized Gains/(Losses) included in Other Comprehen-sive Income				(394,000)
Ending Balance				18,113,000
USDA Securities [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Trading Securities, Unrealized Holding Loss		44,000
Trading Securities, Unrealized Gains				200,000
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning Balance		20,388,000		1,917,319,000
Transfers In		0
Purchases		32,589,000		98,974,000
Sales		(32,589,000)		(3,648,000)
Settlements		(1,704,000)		(86,558,000)
Realized and Unrealized Gains/(Losses) included in Income		(82,000)		259,000
Unrealized Gains/(Losses) included in Other Comprehen-sive Income		0		8,537,000
Ending Balance		18,602,000		1,934,883,000
Available-for-sale Securities [Member] | Investment Securities [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning Balance		17,730,000		44,924,000
Transfers In		7,041,000
Purchases		0		0
Sales		0		(26,806,000)
Settlements		(112,000)		0
Realized and Unrealized Gains/(Losses) included in Income		0		6,000
Unrealized Gains/(Losses) included in Other Comprehen-sive Income		(1,716,000)		(394,000)
Ending Balance		22,943,000		17,730,000
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		4,853,685,000		4,152,605,000
Transfers In		0
Purchases		539,527,000		915,531,000
Sales		0		0
Settlements		(161,907,000)		(513,028,000)
Realized and Unrealized Gains/(Losses) included in Income		(3,215,000)		24,298,000
Unrealized Gains/(Losses) included in Other Comprehen-sive Income		14,956,000		(13,902,000)
Ending Balance		5,243,046,000		4,565,504,000
Available-for-sale Securities [Member] | USDA Securities [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning Balance		0		1,888,344,000
Transfers In		0
Purchases		32,589,000		98,974,000
Sales		(32,589,000)		(3,648,000)
Settlements		0		(84,193,000)
Realized and Unrealized Gains/(Losses) included in Income		0		0
Unrealized Gains/(Losses) included in Other Comprehen-sive Income		0		8,537,000
Ending Balance		0		1,908,014,000
Trading Securities [Member] | Investment Securities [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning Balance				491,000
Purchases				0
Sales				0
Settlements				(206,000)
Realized and Unrealized Gains/(Losses) included in Income				98,000
Unrealized Gains/(Losses) included in Other Comprehen-sive Income				0
Ending Balance				383,000
Trading Securities [Member] | USDA Securities [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning Balance		20,388,000	[1]	28,975,000
Transfers In		0
Purchases		0		0
Sales		0		0
Settlements		(1,704,000)		(2,365,000)
Realized and Unrealized Gains/(Losses) included in Income		(82,000)	[1]	259,000	[2]
Unrealized Gains/(Losses) included in Other Comprehen-sive Income		0		0
Ending Balance		18,602,000	[1]	26,869,000
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		4,853,685,000	[1]	4,121,244,000
Transfers In		0
Purchases		539,527,000		915,531,000
Sales		0		0
Settlements		(161,907,000)		(512,530,000)
Realized and Unrealized Gains/(Losses) included in Income		(3,215,000)		24,298,000
Unrealized Gains/(Losses) included in Other Comprehen-sive Income		14,956,000		(13,733,000)
Ending Balance		5,243,046,000	[1]	4,534,810,000
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				31,361,000
Purchases				0
Sales				0
Settlements				(498,000)
Realized and Unrealized Gains/(Losses) included in Income				0
Unrealized Gains/(Losses) included in Other Comprehen-sive Income				(169,000)
Ending Balance				30,694,000
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		17,730,000		44,924,000
Transfers In		0
Purchases		0		0
Sales		0		(26,806,000)
Settlements		0		0
Realized and Unrealized Gains/(Losses) included in Income		0		6,000
Unrealized Gains/(Losses) included in Other Comprehen-sive Income		394,000		(394,000)
Ending Balance		18,124,000		17,730,000
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				491,000
Purchases				0
Sales				0
Settlements	[3]			(206,000)
Realized and Unrealized Gains/(Losses) included in Income				98,000
Unrealized Gains/(Losses) included in Other Comprehen-sive Income				0
Ending Balance				$ 383,000
Fixed 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		0
Transfers In		7,041,000
Purchases		0
Sales		0
Settlements		(112,000)
Realized and Unrealized Gains/(Losses) included in Income		0
Unrealized Gains/(Losses) included in Other Comprehen-sive Income		(2,110,000)
Ending Balance		$ 4,819,000

[1] Includes unrealized losses of $44,000 attributable to assets still held as of March 31, 2017 that are recorded in "(Losses)/gains on trading securities."

[2] Includes unrealized gains of $0.2 million attributable to assets still held as of March 31, 2016 that are recorded in "(Losses)/gains on trading securities."

[3] Unrealized gains are attributable to assets still held as of March 31, 2016 and are recorded in "(Losses)/gains on trading securities."