Fair Value Disclosures - Unobservable Input Reconciliation (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended			3 Months Ended														3 Months Ended										3 Months Ended									3 Months Ended			0 Months Ended				3 Months Ended															3 Months Ended	12 Months Ended							3 Months Ended	12 Months Ended	3 Months Ended	12 Months Ended	3 Months Ended	12 Months Ended	3 Months Ended	12 Months Ended	3 Months Ended	12 Months Ended	3 Months Ended	12 Months Ended	3 Months Ended	12 Months Ended	3 Months Ended	12 Months Ended	3 Months Ended	12 Months Ended	3 Months Ended	12 Months Ended	3 Months Ended	12 Months Ended	3 Months Ended	12 Months Ended	3 Months Ended	12 Months Ended	3 Months Ended	12 Months Ended	3 Months Ended	12 Months Ended	3 Months Ended	12 Months Ended	3 Months Ended	12 Months Ended	3 Months Ended	12 Months Ended	3 Months Ended	12 Months Ended	3 Months Ended	12 Months Ended	3 Months Ended	12 Months Ended
	Mar. 31, 2013 Fair Value, Measurements, Recurring [Member] Level 3	Mar. 31, 2012 Fair Value, Measurements, Recurring [Member] Level 3	Dec. 31, 2012 Fair Value, Measurements, Recurring [Member] Level 3	Mar. 31, 2013 Fair Value, Measurements, Recurring [Member] Level 3 Derivative Financial Instruments, Liabilities [Member]		Mar. 31, 2012 Fair Value, Measurements, Recurring [Member] Level 3 Derivative Financial Instruments, Liabilities [Member]		Mar. 31, 2013 Fair Value, Measurements, Recurring [Member] Level 3 Available-for-sale Securities [Member]	Mar. 31, 2012 Fair Value, Measurements, Recurring [Member] Level 3 Available-for-sale Securities [Member]	Mar. 31, 2013 Fair Value, Measurements, Recurring [Member] Level 3 Trading Account Assets [Member]	Mar. 31, 2012 Fair Value, Measurements, Recurring [Member] Level 3 Trading Account Assets [Member]	Mar. 31, 2013 Fair Value, Measurements, Recurring [Member] Level 3	Mar. 31, 2012 Fair Value, Measurements, Recurring [Member] Level 3	Mar. 31, 2013 Fair Value, Measurements, Recurring [Member] Level 3 Investment Securities [Member]	Mar. 31, 2012 Fair Value, Measurements, Recurring [Member] Level 3 Investment Securities [Member]	Mar. 31, 2013 Farmer Mac Guarantee	Mar. 31, 2012 Farmer Mac Guarantee	Mar. 31, 2013 Farmer Mac Guarantee Fair Value, Measurements, Recurring [Member] Level 3	Mar. 31, 2012 Farmer Mac Guarantee Fair Value, Measurements, Recurring [Member] Level 3	Mar. 31, 2013 Farmer Mac Guarantee Fair Value, Measurements, Recurring [Member] Level 3 Farmer Mac Guaranteed Securities [Member]	Dec. 31, 2012 Farmer Mac Guarantee Fair Value, Measurements, Recurring [Member] Level 3 Farmer Mac Guaranteed Securities [Member]	Mar. 31, 2013 Farmer Mac Guarantee Fair Value, Measurements, Recurring [Member] Level 3 Farm & Ranch Guaranteed Securities [Member]	Dec. 31, 2012 Farmer Mac Guarantee Fair Value, Measurements, Recurring [Member] Level 3 Farm & Ranch Guaranteed Securities [Member]	Mar. 31, 2013 Farmer Mac Guarantee Fair Value, Measurements, Recurring [Member] Level 3	Dec. 31, 2012 Farmer Mac Guarantee Fair Value, Measurements, Recurring [Member] Level 3	Mar. 31, 2013 Farmer Mac Guarantee Fair Value, Measurements, Recurring [Member] Level 3 Farmer Mac Guaranteed Securities - Rural Utilities	Dec. 31, 2012 Farmer Mac Guarantee Fair Value, Measurements, Recurring [Member] Level 3 Farmer Mac Guaranteed Securities - Rural Utilities	Mar. 31, 2013 Fair Value, Measurements, Recurring [Member] Level 3		Mar. 31, 2012 Fair Value, Measurements, Recurring [Member] Level 3		Mar. 31, 2013 Fair Value, Measurements, Recurring [Member] Level 3	Mar. 31, 2012 Fair Value, Measurements, Recurring [Member] Level 3	Dec. 31, 2012 Fair Value, Measurements, Recurring [Member] Level 3	Mar. 31, 2013 Auction-rate certificates backed by Government guaranteed student loans Floating Interest Rate [Member]	Dec. 31, 2012 Auction-rate certificates backed by Government guaranteed student loans Floating Interest Rate [Member]	Mar. 31, 2013 Auction-rate certificates backed by Government guaranteed student loans Fair Value, Measurements, Recurring [Member] Level 3 Floating Interest Rate [Member]	Mar. 31, 2012 Auction-rate certificates backed by Government guaranteed student loans Fair Value, Measurements, Recurring [Member] Level 3 Floating Interest Rate [Member]	Dec. 31, 2012 Auction-rate certificates backed by Government guaranteed student loans Fair Value, Measurements, Recurring [Member] Level 3 Floating Interest Rate [Member]	Mar. 31, 2013 Asset-backed Securities [Member] Floating Interest Rate [Member]	Dec. 31, 2012 Asset-backed Securities [Member] Floating Interest Rate [Member]	Mar. 31, 2013 Asset-backed Securities [Member] Fair Value, Measurements, Recurring [Member] Level 3 Floating Interest Rate [Member]	Dec. 31, 2012 Asset-backed Securities [Member] Fair Value, Measurements, Recurring [Member] Level 3 Floating Interest Rate [Member]	Mar. 31, 2013 Asset-backed Securities [Member] Fair Value, Measurements, Recurring [Member] Level 3 Trading Account Assets [Member] Floating Interest Rate [Member]		Mar. 31, 2012 Asset-backed Securities [Member] Fair Value, Measurements, Recurring [Member] Level 3 Trading Account Assets [Member] Floating Interest Rate [Member]		Mar. 31, 2013 Asset-backed Securities [Member] Fair Value, Measurements, Recurring [Member] Level 3	Mar. 31, 2012 Asset-backed Securities [Member] Fair Value, Measurements, Recurring [Member] Level 3	Mar. 31, 2013 Farm & Ranch [Member] Farmer Mac Guarantee Fair Value, Measurements, Recurring [Member] Level 3	Mar. 31, 2012 Farm & Ranch [Member] Farmer Mac Guarantee Fair Value, Measurements, Recurring [Member] Level 3	Mar. 31, 2013 Farmer Mac Guarantee Fair Value, Measurements, Recurring [Member] Level 3	Mar. 31, 2012 Farmer Mac Guarantee Fair Value, Measurements, Recurring [Member] Level 3	Mar. 31, 2013 Rural Utilities [Member] Farmer Mac Guarantee Fair Value, Measurements, Recurring [Member] Level 3	Mar. 31, 2012 Rural Utilities [Member] Farmer Mac Guarantee Fair Value, Measurements, Recurring [Member] Level 3	Mar. 31, 2013 Indicative Bid Approach Valuation Technique [Member] Fair Value, Measurements, Recurring [Member] Auction-rate certificates backed by Government guaranteed student loans Floating Interest Rate [Member]	Dec. 31, 2012 Indicative Bid Approach Valuation Technique [Member] Fair Value, Measurements, Recurring [Member] Auction-rate certificates backed by Government guaranteed student loans Floating Interest Rate [Member]	Mar. 31, 2013 Discounted Cash Flows Approach Valuation Technique Fair Value, Measurements, Recurring [Member] Collateralized Mortgage Backed Securities [Member] Floating Interest Rate [Member]	Mar. 31, 2013 Discounted Cash Flows Approach Valuation Technique Fair Value, Measurements, Recurring [Member] Level 3 Asset-backed Securities [Member] Floating Interest Rate [Member]	Dec. 31, 2012 Discounted Cash Flows Approach Valuation Technique Fair Value, Measurements, Recurring [Member] Level 3 Asset-backed Securities [Member] Floating Interest Rate [Member]	Mar. 31, 2013 Discounted Cash Flows Approach Valuation Technique Farmer Mac Guarantee Fair Value, Measurements, Recurring [Member] Farm & Ranch Guaranteed Securities [Member]	Dec. 31, 2012 Discounted Cash Flows Approach Valuation Technique Farmer Mac Guarantee Fair Value, Measurements, Recurring [Member] Farm & Ranch Guaranteed Securities [Member]	Mar. 31, 2013 Discounted Cash Flows Approach Valuation Technique Farmer Mac Guarantee Fair Value, Measurements, Recurring [Member]	Dec. 31, 2012 Discounted Cash Flows Approach Valuation Technique Farmer Mac Guarantee Fair Value, Measurements, Recurring [Member]	Mar. 31, 2013 Discounted Cash Flows Approach Valuation Technique Farmer Mac Guarantee Fair Value, Measurements, Recurring [Member] Farmer Mac Guaranteed Securities - Rural Utilities	Dec. 31, 2012 Discounted Cash Flows Approach Valuation Technique Farmer Mac Guarantee Fair Value, Measurements, Recurring [Member] Farmer Mac Guaranteed Securities - Rural Utilities	Mar. 31, 2013 Minimum [Member] Indicative Bid Approach Valuation Technique [Member] Fair Value, Measurements, Recurring [Member] Level 3 Auction-rate certificates backed by Government guaranteed student loans Floating Interest Rate [Member]	Dec. 31, 2012 Minimum [Member] Indicative Bid Approach Valuation Technique [Member] Fair Value, Measurements, Recurring [Member] Level 3 Auction-rate certificates backed by Government guaranteed student loans Floating Interest Rate [Member]	Mar. 31, 2013 Minimum [Member] Discounted Cash Flows Approach Valuation Technique Fair Value, Measurements, Recurring [Member] Level 3 Derivative Financial Instruments, Liabilities [Member]	Dec. 31, 2012 Minimum [Member] Discounted Cash Flows Approach Valuation Technique Fair Value, Measurements, Recurring [Member] Level 3 Derivative Financial Instruments, Liabilities [Member]	Mar. 31, 2013 Minimum [Member] Discounted Cash Flows Approach Valuation Technique Fair Value, Measurements, Recurring [Member] Level 3 Asset-backed Securities [Member] Floating Interest Rate [Member]	Dec. 31, 2012 Minimum [Member] Discounted Cash Flows Approach Valuation Technique Fair Value, Measurements, Recurring [Member] Level 3 Asset-backed Securities [Member] Floating Interest Rate [Member]	Mar. 31, 2013 Minimum [Member] Discounted Cash Flows Approach Valuation Technique Farmer Mac Guarantee Fair Value, Measurements, Recurring [Member] Level 3 Farm & Ranch Guaranteed Securities [Member]	Dec. 31, 2012 Minimum [Member] Discounted Cash Flows Approach Valuation Technique Farmer Mac Guarantee Fair Value, Measurements, Recurring [Member] Level 3 Farm & Ranch Guaranteed Securities [Member]	Mar. 31, 2013 Minimum [Member] Discounted Cash Flows Approach Valuation Technique Farmer Mac Guarantee Fair Value, Measurements, Recurring [Member] Level 3	Dec. 31, 2012 Minimum [Member] Discounted Cash Flows Approach Valuation Technique Farmer Mac Guarantee Fair Value, Measurements, Recurring [Member] Level 3	Mar. 31, 2013 Minimum [Member] Discounted Cash Flows Approach Valuation Technique Farmer Mac Guarantee Fair Value, Measurements, Recurring [Member] Level 3 Farmer Mac Guaranteed Securities - Rural Utilities	Dec. 31, 2012 Minimum [Member] Discounted Cash Flows Approach Valuation Technique Farmer Mac Guarantee Fair Value, Measurements, Recurring [Member] Level 3 Farmer Mac Guaranteed Securities - Rural Utilities	Mar. 31, 2013 Minimum [Member] Discounted Cash Flows Approach Valuation Technique Fair Value, Measurements, Recurring [Member] Level 3	Dec. 31, 2012 Minimum [Member] Discounted Cash Flows Approach Valuation Technique Fair Value, Measurements, Recurring [Member] Level 3	Mar. 31, 2013 Maximum [Member] Indicative Bid Approach Valuation Technique [Member] Fair Value, Measurements, Recurring [Member] Level 3 Auction-rate certificates backed by Government guaranteed student loans Floating Interest Rate [Member]	Dec. 31, 2012 Maximum [Member] Indicative Bid Approach Valuation Technique [Member] Fair Value, Measurements, Recurring [Member] Level 3 Auction-rate certificates backed by Government guaranteed student loans Floating Interest Rate [Member]	Mar. 31, 2013 Maximum [Member] Discounted Cash Flows Approach Valuation Technique Fair Value, Measurements, Recurring [Member] Level 3 Derivative Financial Instruments, Liabilities [Member]	Dec. 31, 2012 Maximum [Member] Discounted Cash Flows Approach Valuation Technique Fair Value, Measurements, Recurring [Member] Level 3 Derivative Financial Instruments, Liabilities [Member]	Mar. 31, 2013 Maximum [Member] Discounted Cash Flows Approach Valuation Technique Fair Value, Measurements, Recurring [Member] Level 3 Asset-backed Securities [Member] Floating Interest Rate [Member]	Dec. 31, 2012 Maximum [Member] Discounted Cash Flows Approach Valuation Technique Fair Value, Measurements, Recurring [Member] Level 3 Asset-backed Securities [Member] Floating Interest Rate [Member]	Mar. 31, 2013 Maximum [Member] Discounted Cash Flows Approach Valuation Technique Farmer Mac Guarantee Fair Value, Measurements, Recurring [Member] Level 3 Farm & Ranch Guaranteed Securities [Member]	Dec. 31, 2012 Maximum [Member] Discounted Cash Flows Approach Valuation Technique Farmer Mac Guarantee Fair Value, Measurements, Recurring [Member] Level 3 Farm & Ranch Guaranteed Securities [Member]	Mar. 31, 2013 Maximum [Member] Discounted Cash Flows Approach Valuation Technique Farmer Mac Guarantee Fair Value, Measurements, Recurring [Member] Level 3	Dec. 31, 2012 Maximum [Member] Discounted Cash Flows Approach Valuation Technique Farmer Mac Guarantee Fair Value, Measurements, Recurring [Member] Level 3	Mar. 31, 2013 Maximum [Member] Discounted Cash Flows Approach Valuation Technique Farmer Mac Guarantee Fair Value, Measurements, Recurring [Member] Level 3 Farmer Mac Guaranteed Securities - Rural Utilities	Dec. 31, 2012 Maximum [Member] Discounted Cash Flows Approach Valuation Technique Farmer Mac Guarantee Fair Value, Measurements, Recurring [Member] Level 3 Farmer Mac Guaranteed Securities - Rural Utilities	Mar. 31, 2013 Maximum [Member] Discounted Cash Flows Approach Valuation Technique Fair Value, Measurements, Recurring [Member] Level 3	Dec. 31, 2012 Maximum [Member] Discounted Cash Flows Approach Valuation Technique Fair Value, Measurements, Recurring [Member] Level 3	Mar. 31, 2013 Weighted Average Indicative Bid Approach Valuation Technique [Member] Fair Value, Measurements, Recurring [Member] Level 3 Auction-rate certificates backed by Government guaranteed student loans Floating Interest Rate [Member]	Dec. 31, 2012 Weighted Average Indicative Bid Approach Valuation Technique [Member] Fair Value, Measurements, Recurring [Member] Level 3 Auction-rate certificates backed by Government guaranteed student loans Floating Interest Rate [Member]	Mar. 31, 2013 Weighted Average Discounted Cash Flows Approach Valuation Technique Fair Value, Measurements, Recurring [Member] Level 3 Derivative Financial Instruments, Liabilities [Member]	Dec. 31, 2012 Weighted Average Discounted Cash Flows Approach Valuation Technique Fair Value, Measurements, Recurring [Member] Level 3 Derivative Financial Instruments, Liabilities [Member]	Mar. 31, 2013 Weighted Average Discounted Cash Flows Approach Valuation Technique Fair Value, Measurements, Recurring [Member] Level 3 Asset-backed Securities [Member] Floating Interest Rate [Member]	Dec. 31, 2012 Weighted Average Discounted Cash Flows Approach Valuation Technique Fair Value, Measurements, Recurring [Member] Level 3 Asset-backed Securities [Member] Floating Interest Rate [Member]	Mar. 31, 2013 Weighted Average Discounted Cash Flows Approach Valuation Technique Farmer Mac Guarantee Fair Value, Measurements, Recurring [Member] Level 3 Farm & Ranch Guaranteed Securities [Member]	Dec. 31, 2012 Weighted Average Discounted Cash Flows Approach Valuation Technique Farmer Mac Guarantee Fair Value, Measurements, Recurring [Member] Level 3 Farm & Ranch Guaranteed Securities [Member]	Mar. 31, 2013 Weighted Average Discounted Cash Flows Approach Valuation Technique Farmer Mac Guarantee Fair Value, Measurements, Recurring [Member] Level 3	Dec. 31, 2012 Weighted Average Discounted Cash Flows Approach Valuation Technique Farmer Mac Guarantee Fair Value, Measurements, Recurring [Member] Level 3	Mar. 31, 2013 Weighted Average Discounted Cash Flows Approach Valuation Technique Farmer Mac Guarantee Fair Value, Measurements, Recurring [Member] Level 3 Farmer Mac Guaranteed Securities - Rural Utilities	Dec. 31, 2012 Weighted Average Discounted Cash Flows Approach Valuation Technique Farmer Mac Guarantee Fair Value, Measurements, Recurring [Member] Level 3 Farmer Mac Guaranteed Securities - Rural Utilities	Mar. 31, 2013 Weighted Average Discounted Cash Flows Approach Valuation Technique Fair Value, Measurements, Recurring [Member] Level 3	Dec. 31, 2012 Weighted Average Discounted Cash Flows Approach Valuation Technique Fair Value, Measurements, Recurring [Member] Level 3
Fair Value, Assets and Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Available-for-sale Securities, Fair Value Disclosure	$ 65,446		$ 63,159													$ 5,100,080	$ 4,766,258			$ 5,100,080	$ 4,766,258	$ 3,528,520	$ 3,426,489	$ 27,198	$ 26,681	$ 1,544,362	$ 1,313,088					$ 1,569,160		$ 1,486,595	$ 65,213	$ 63,159	$ 65,213		$ 63,159	$ 146,678	$ 151,044	$ 0	$ 0													$ 65,213	$ 63,159	$ 233			$ 3,528,520	$ 3,426,489	$ 27,198	$ 26,681	$ 1,544,362	$ 1,313,088
Fair Value Inputs, Range of Offered Quotes																																																																			82.00%	82.00%													93.00%	90.00%													88.00%	85.00%
Trading Securities, Unrealized Gains													800																											0	0
Trading Securities, Unrealized Holding Loss												100																												2,884	3,080
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning Balance, Asset	6,421,447	5,843,186						63,159	60,213	1,247	1,796			64,406	62,009			4,766,258	4,289,272									104,188	[1]	212,359	[2]	1,590,783	1,491,905				63,159	60,213						1,247	[3]	1,796	[4]	1,486,595	1,279,546	3,426,489	2,807,627	26,681	35,599	1,313,088	1,446,046
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Purchases	547,420	301,725						233	0	0	0			233	0			425,000	200,000									0	[1]	0	[2]	122,187	101,725				0	0						0	[3]	0	[4]	122,187	101,725	100,000	200,000	0	0	325,000	0
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Sales	0	0						0	0	0	0			0	0			0	0									0	[1]	0	[2]	0	0				0	0						0	[3]	0	[4]	0	0	0	0	0	0	0	0
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Settlements	(164,763)	(179,166)						0	0	(314)	(288)			(314)	(288)			(78,316)	(95,937)									(16,931)	[1]	(28,923)	[2]	(86,133)	(82,941)				0	0						(314)	[3]	(288)	[4]	(69,202)	(54,018)	(9)	(8)	(383)	(228)	(77,924)	(95,701)
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Gain (Loss) Included in Earnings	(2,928)	1,099						0	0	196	138			196	138			(3,138)	0									14	[1]	961	[2]	14	961				0	0						196	[3]	138	[4]	0	0	(3,138)	0	0	0	0	0
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Gain (Loss) Included in Other Comprehensive Income (Loss)	21,910	(3,370)						2,054	(1,345)	0	0			2,054	(1,345)			(9,724)	(3,474)									0	[1]	0	[2]	29,580	1,449				2,054	(1,345)						0	[3]	0	[4]	29,580	1,449	5,178	604	900	758	(15,802)	(4,836)
Ending Balance, Asset	6,823,086	5,963,474						65,446	58,868	1,129	1,646			66,575	60,514			5,100,080	4,389,861									87,271	[1]	184,397	[2]	1,656,431	1,513,099				65,213	58,868						1,129	[3]	1,646	[4]	1,569,160	1,328,702	3,528,520	3,008,223	27,198	36,129	1,544,362	1,345,509
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning Balance, Liability	(691)	(1,335)		(691)	[5]	(1,335)	[6]
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Liability, Purchases	0	0		0	[5]	0	[6]
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Liability, Sales	0	0		0	[5]	0	[6]
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Liability, Settlements	0	0		0	[5]	0	[6]
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Liability, Gain (Loss) Included in Earnings	159	110		159	[5]	110	[6]
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Liability, Gain (Loss) Included in Other Comprehensive Income (Loss)	0	0		0	[5]	0	[6]
Ending Balance, Liability	$ (532)	$ (1,225)		$ (532)	[5]	$ (1,225)	[6]
Fair Value Inputs, discount rate																																																																					0.60%	1.00%	11.90%	12.40%	0.90%	1.10%	0.80%	1.00%	0.80%	0.80%	1.20%	1.40%			2.40%	3.00%	19.40%	19.70%	3.50%	3.40%	3.30%	3.40%	3.00%	2.90%	5.30%	5.30%			1.30%	1.70%	15.90%	16.20%	1.60%	1.60%	1.90%	2.10%	1.60%	1.60%	3.10%	3.40%
Fair Value Inputs, Constant Prepayment Rate																																																											10.00%	10.00%									12.00%	11.00%					8.00%	8.00%			0.00%	0.00%			17.00%	19.00%					18.00%	17.00%			27.00%	26.00%			16.00%	16.00%					15.00%	14.00%			9.00%	10.00%

[1] Includes unrealized gains of $0.8 million attributable to assets still held as of December 31, 2012 that are recorded in Gains on trading assets.

[2] Includes unrealized losses of $0.1 million attributable to assets still held as of March 31, 2013 that are recorded in Gains on trading assets.

[3] Unrealized gains are attributable to assets still held as of March 31, 2013 and are recorded in Gains on trading assets.

[4] Unrealized gains are attributable to assets still held as of December 31, 2012 and are recorded in Gains on trading assets.

[5] Unrealized gains are attributable to liabilities still held as of March 31, 2013 and are recorded in 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 Gains on financial derivatives and hedging activities.