Fair Value Disclosures - Unobservable Input Reconciliation (Details) (USD $) In Thousands, unless otherwise specified	9 Months Ended	12 Months Ended		9 Months Ended		12 Months Ended				9 Months Ended	12 Months Ended		9 Months Ended	12 Months Ended					9 Months Ended	12 Months Ended		9 Months Ended	12 Months Ended				9 Months Ended		12 Months Ended				9 Months Ended	12 Months Ended		9 Months Ended	12 Months Ended		0 Months Ended		9 Months Ended		12 Months Ended				9 Months Ended	12 Months Ended		9 Months Ended	12 Months Ended		9 Months Ended	12 Months Ended			9 Months Ended	12 Months Ended
	Sep. 30, 2011 Fair Value, Measurements, Recurring [Member] Level 3	Dec. 31, 2012 Fair Value, Measurements, Recurring [Member] Level 3	Dec. 31, 2010 Fair Value, Measurements, Recurring [Member] Level 3	Sep. 30, 2011 Fair Value, Measurements, Recurring [Member] Level 3 Derivative Financial Instruments, Liabilities [Member]		Dec. 31, 2012 Fair Value, Measurements, Recurring [Member] Level 3 Derivative Financial Instruments, Liabilities [Member]		Dec. 31, 2010 Fair Value, Measurements, Recurring [Member] Level 3 Derivative Financial Instruments, Liabilities [Member]		Sep. 30, 2011 Fair Value, Measurements, Recurring [Member] Level 3 Available-for-sale Securities [Member]	Dec. 31, 2012 Fair Value, Measurements, Recurring [Member] Level 3 Available-for-sale Securities [Member]	Dec. 31, 2010 Fair Value, Measurements, Recurring [Member] Level 3 Available-for-sale Securities [Member]	Sep. 30, 2011 Fair Value, Measurements, Recurring [Member] Level 3 Trading Account Assets [Member]	Dec. 31, 2012 Fair Value, Measurements, Recurring [Member] Level 3 Trading Account Assets [Member]	Dec. 31, 2010 Fair Value, Measurements, Recurring [Member] Level 3 Trading Account Assets [Member]	Dec. 31, 2012 Fair Value, Measurements, Recurring [Member] Level 3	Dec. 31, 2011 Fair Value, Measurements, Recurring [Member] Level 3	Dec. 31, 2010 Fair Value, Measurements, Recurring [Member] Level 3	Sep. 30, 2011 Fair Value, Measurements, Recurring [Member] Level 3 Investment Securities [Member]	Dec. 31, 2012 Fair Value, Measurements, Recurring [Member] Level 3 Investment Securities [Member]	Dec. 31, 2010 Fair Value, Measurements, Recurring [Member] Level 3 Investment Securities [Member]	Sep. 30, 2011 Farmer Mac Guarantee Fair Value, Measurements, Recurring [Member] Level 3	Dec. 31, 2012 Farmer Mac Guarantee Fair Value, Measurements, Recurring [Member] Level 3	Dec. 31, 2010 Farmer Mac Guarantee Fair Value, Measurements, Recurring [Member] Level 3	Dec. 31, 2010 Farmer Mac Guarantee Fair Value, Measurements, Recurring [Member] Level 3 Available-for-sale Securities [Member]	Dec. 31, 2010 Farmer Mac Guarantee Fair Value, Measurements, Recurring [Member] Level 3 Trading Account Assets [Member]	Sep. 30, 2011 Fair Value, Measurements, Recurring [Member] Level 3		Dec. 31, 2012 Fair Value, Measurements, Recurring [Member] Level 3		Dec. 31, 2010 Fair Value, Measurements, Recurring [Member] Level 3		Sep. 30, 2011 Fair Value, Measurements, Recurring [Member] Level 3	Dec. 31, 2012 Fair Value, Measurements, Recurring [Member] Level 3	Dec. 31, 2010 Fair Value, Measurements, Recurring [Member] Level 3	Sep. 30, 2011 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]	Dec. 31, 2010 Auction-rate certificates backed by Government guaranteed student loans Fair Value, Measurements, Recurring [Member] Level 3 Floating Interest Rate [Member]	Dec. 31, 2012 Asset-backed Securities [Member] Floating Interest Rate [Member]	Dec. 31, 2011 Asset-backed Securities [Member] Floating Interest Rate [Member]	Sep. 30, 2011 Asset-backed Securities [Member] Fair Value, Measurements, Recurring [Member] Level 3 Trading Account Assets [Member] Floating Interest Rate [Member]		Dec. 31, 2012 Asset-backed Securities [Member] Fair Value, Measurements, Recurring [Member] Level 3 Trading Account Assets [Member] Floating Interest Rate [Member]		Dec. 31, 2010 Asset-backed Securities [Member] Fair Value, Measurements, Recurring [Member] Level 3 Trading Account Assets [Member] Floating Interest Rate [Member]		Sep. 30, 2011 Asset-backed Securities [Member] Fair Value, Measurements, Recurring [Member] Level 3	Dec. 31, 2012 Asset-backed Securities [Member] Fair Value, Measurements, Recurring [Member] Level 3	Dec. 31, 2010 Asset-backed Securities [Member] Fair Value, Measurements, Recurring [Member] Level 3	Sep. 30, 2011 Farmer Mac I [Member] Farmer Mac Guarantee Fair Value, Measurements, Recurring [Member] Level 3	Dec. 31, 2012 Farmer Mac I [Member] Farmer Mac Guarantee Fair Value, Measurements, Recurring [Member] Level 3	Dec. 31, 2010 Farmer Mac I [Member] Farmer Mac Guarantee Fair Value, Measurements, Recurring [Member] Level 3	Sep. 30, 2011 Farmer Mac II [Member] Farmer Mac Guarantee Fair Value, Measurements, Recurring [Member] Level 3	Dec. 31, 2012 Farmer Mac II [Member] Farmer Mac Guarantee Fair Value, Measurements, Recurring [Member] Level 3	Dec. 31, 2010 Farmer Mac II [Member] Farmer Mac Guarantee Fair Value, Measurements, Recurring [Member] Level 3	Dec. 31, 2010 Farmer Mac II [Member] Farmer Mac Guarantee Fair Value, Measurements, Recurring [Member] Level 3 Trading Account Assets [Member]	Sep. 30, 2011 Rural Utilities [Member] Farmer Mac Guarantee Fair Value, Measurements, Recurring [Member] Level 3	Dec. 31, 2012 Rural Utilities [Member] Farmer Mac Guarantee Fair Value, Measurements, Recurring [Member] Level 3	Dec. 31, 2010 Rural Utilities [Member] Farmer Mac Guarantee Fair Value, Measurements, Recurring [Member] Level 3	Dec. 31, 2010 Rural Utilities [Member] Farmer Mac Guarantee Fair Value, Measurements, Recurring [Member] Level 3 Trading Account Assets [Member]
Fair Value, Assets and Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Trading Securities, Unrealized Gains																$ 300																							$ 0	$ 0
Trading Securities, Unrealized Holding Loss																	1,800	2,000																					3,080	3,342
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning Balance, Asset	4,290,443	5,843,186	3,698,625							64,335	60,213	209,657	1,400	1,796	89,972				65,735	62,009	299,629	2,907,264	4,289,272	3,398,996	2,524,867	874,129	311,765	[1]	212,359	[2]	0	[1]	1,317,444	1,491,905	0	64,335	60,213	72,884			1,400	[3]	1,796	[4]	1,824	[3]	1,005,679	1,279,546	0	942,809	2,807,627	56,864	37,637	35,599	764,792	422,681	1,926,818	1,446,046	1,703,211	451,448
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Purchases	2,209,604	1,469,057								0	0		0	0					0	0		1,804,768	989,733				0	[1]	0	[2]			404,836	479,324		0	0				0	[3]	0	[4]			404,836	479,324		1,801,500	601,000		3,268	5,327			0	383,406
Sales, Asset	(3,268)	(5,327)								0	0		0	0					0	0		(3,268)	(5,327)				0	[1]	0	[2]			0	0		0	0				0	[3]	0	[4]			0	0		0	0		(3,268)	(5,327)			0	0
Settlements, Asset	(758,897)	(873,152)								0	0		(822)	(812)					(822)	(812)		(482,765)	(507,440)				(102,525)	[1]	(108,215)	[2]			(275,310)	(364,900)		0	0				(822)	[3]	(812)	[4]			(172,785)	(256,685)		(2,031)	(2,832)		(4,334)	(8,907)			(476,400)	(495,701)
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Gain (Loss) Included in Earnings	4,337	6,695	2,899							0	0	0	1,218	263	324				1,218	263	324	0	6,388	0	0	0	3,119	[1]	44	[2]	2,575		3,119	44	2,575	0	0	0			1,218	[3]	263	[4]	324		0	0	0	0	6,388	0	0	0	0	0	0	0	0	0
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Gain (Loss) Included in Other Comprehensive Income (Loss)	100,967	(19,012)	3,660							(4,122)	2,946	(8,549)	0	0	0				(4,122)	2,946	(8,549)	63,273	(6,368)	7,701	7,701	0	0	[1]	0	[2]	0		41,816	(15,590)	4,508	(4,122)	2,946	(8,549)			0	[3]	0	[4]	0		41,816	(15,590)	4,508	65,349	14,306	(1,340)	2,296	(11)	(2,364)	0	(4,372)	(20,663)	11,405	0
Ending Balance, Asset	5,843,186	6,421,447	4,290,443							60,213	63,159	64,335	1,796	1,247	1,400				62,009	64,406	65,735	4,289,272	4,766,258	2,907,264	2,907,264	0	212,359	[1]	104,188	[2]	311,765	[1]	1,491,905	1,590,783	1,317,444	60,213	63,159	64,335			1,796	[3]	1,247	[4]	1,400	[3]	1,279,546	1,486,595	1,005,679	2,807,627	3,426,489	942,809	35,599	26,681	37,637	0	1,446,046	1,313,088	1,926,818	0
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning Balance, Liability	(3,390)	(1,335)	(3,653)	(3,390)	[5]	(1,335)	[6]	(3,653)	[5]
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	2,055	644	263	2,055	[5]	644	[6]	263
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Liability, Gain (Loss) Included in Other Comprehensive Income (Loss)	0	0	0	0	[5]	0	[6]	0
Ending Balance, Liability	$ (1,335)	$ (691)	$ (3,390)	$ (1,335)	[5]	$ (691)	[6]	$ (3,390)	[5]

[1] Includes unrealized gains of $0.3 million attributable to assets still held as of December 31, 2012 that are recorded in Gains on trading assets.

[2] Includes unrealized losses of $1.8 million attributable to assets still held as of December 31, 2011 that are recorded in Gains on trading assets.

[3] Unrealized gains are attributable to assets still held as of December 31, 2011 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 December 31, 2011 and are recorded in Losses 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 on financial derivatives and hedging activities.