Guarantees and Commitments - Credit Quality Indicators (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020	Dec. 31, 2020
Total
Total	$ 7,758,286		$ 7,758,286		$ 7,261,933
Rural Utilities
Year One
Total	60,793		60,793		667,489
Current period charge-offs	0	$ 0	0	$ 0
Current period recoveries	0	0	0	0
Current period, net charge offs	0	0	0	0
Year Two
Total	642,972		642,972		809,921
Current period charge-offs	0	0	0	0
Current period recoveries	0	0	0	0
Current period, net charge offs	0	0	0	0
Year Three
Total	784,153		784,153		8,260
Current period charge-offs	0	0	0	0
Current period recoveries	0	0	0	0
Current period, net charge offs	0	0	0	0
Year Four
Total	8,100		8,100		89,842
Current period charge-offs	0	0	0	0
Current period recoveries	0	0	0	0
Current period, net charge offs	0	0	0	0
Year Five
Total	89,263		89,263		31,275
Current period charge-offs	0	0	0	0
Current period recoveries	0	0	0	0
Current period, net charge offs	0	0	0	0
Prior
Total	628,903		628,903		641,145
Current period charge-offs	0	0	0	0
Current period recoveries	0	0	0	0
Current period, net charge offs	0	0	0	0
Revolving Loans - Amortized Cost Basis
Total	28,988		28,988		12,480
Current period charge-offs	0	0	0	0
Current period recoveries	0	0	0	0
Current period, net charge offs	0	0	0	0
Total
Current period charge-offs	0	0	0	0
Current period recoveries	0	0	0	0
Current period, net charge offs	0	0	0	0
Total	2,243,172		2,243,172		2,260,412
Farm & Ranch
Year One
Total	1,654,597		1,654,597		2,021,189
Current period charge-offs	0	0	0	0
Current period recoveries	0	0	0	0
Current period, net charge offs	0	0	0	0
Year Two
Total	1,892,856		1,892,856		859,880
Current period charge-offs	0	0	0	0
Current period recoveries	0	0	0	0
Current period, net charge offs	0	0	0	0
Year Three
Total	723,427		723,427		524,541
Current period charge-offs	0	0	0	0
Current period recoveries	0	0	0	0
Current period, net charge offs	0	0	0	0
Year Four
Total	423,585		423,585		562,007
Current period charge-offs	0	0	0	0
Current period recoveries	0	0	0	0
Current period, net charge offs	0	0	0	0
Year Five
Total	375,483		375,483		515,561
Current period charge-offs	0	0	0	0
Current period recoveries	0	0	0	0
Current period, net charge offs	0	0	0	0
Prior
Total	1,154,262		1,154,262		1,140,603
Current period charge-offs	0	0	0	394
Current period recoveries	0	0	0	0
Current period, net charge offs	0	0	0	394
Revolving Loans - Amortized Cost Basis
Total	553,539		553,539		552,657
Current period charge-offs	0	0	0	0
Current period recoveries	0	0	0	0
Current period, net charge offs	0	0	0	0
Total
Current period charge-offs	0	0	0	394
Current period recoveries	0	0	0	0
Current period, net charge offs	0	0	0	394
Total	6,777,749		6,777,749		6,176,438
Acceptable | Rural Utilities
Year One
Total	60,793		60,793		667,489
Year Two
Total	619,772		619,772		809,921
Year Three
Total	784,153		784,153		8,260
Year Four
Total	8,100		8,100		89,842
Year Five
Total	89,263		89,263		31,275
Prior
Total	628,903		628,903		641,145
Revolving Loans - Amortized Cost Basis
Total	28,988		28,988		12,480
Total
Total	2,219,972		2,219,972		2,260,412
Acceptable | Farm & Ranch
Year One
Total	1,570,766		1,570,766		1,947,618
Year Two
Total	1,798,703		1,798,703		774,315
Year Three
Total	660,485		660,485		484,345
Year Four
Total	382,027		382,027		500,768
Year Five
Total	318,043		318,043		465,277
Prior
Total	1,054,024		1,054,024		1,068,693
Revolving Loans - Amortized Cost Basis
Total	531,063		531,063		535,742
Total
Total	6,315,111		6,315,111		5,776,758
Special mention | Rural Utilities
Year One
Total	0		0		0
Year Two
Total	0		0		0
Year Three
Total	0		0		0
Year Four
Total	0		0		0
Year Five
Total	0		0		0
Prior
Total	0		0		0
Revolving Loans - Amortized Cost Basis
Total	0		0		0
Total
Total	0		0		0
Special mention | Farm & Ranch
Year One
Total	83,224		83,224		70,171
Year Two
Total	88,848		88,848		79,744
Year Three
Total	36,050		36,050		18,317
Year Four
Total	13,828		13,828		8,530
Year Five
Total	6,962		6,962		13,111
Prior
Total	18,998		18,998		21,328
Revolving Loans - Amortized Cost Basis
Total	10,531		10,531		7,656
Total
Total	258,441		258,441		218,857
Substandard | Rural Utilities
Year One
Total	0		0		0
Year Two
Total	23,200		23,200		0
Year Three
Total	0		0		0
Year Four
Total	0		0		0
Year Five
Total	0		0		0
Prior
Total	0		0		0
Revolving Loans - Amortized Cost Basis
Total	0		0		0
Total
Total	23,200		23,200		0
Substandard | Farm & Ranch
Year One
Total	607		607		3,400
Year Two
Total	5,305		5,305		5,821
Year Three
Total	26,892		26,892		21,879
Year Four
Total	27,730		27,730		52,709
Year Five
Total	50,478		50,478		37,173
Prior
Total	81,240		81,240		50,582
Revolving Loans - Amortized Cost Basis
Total	11,945		11,945		9,259
Total
Total	204,197		204,197		180,823
LTSPCs and Farmer Mac Guaranteed Securities | Farm & Ranch
Year One
Total	306,664		306,664		182,397
Current period charge-offs	0	0	0	0
Current period recoveries	0	0	0	0
Current period, net charge offs	0	0	0	0
Year Two
Total	314,073		314,073		225,612
Current period charge-offs	0	0	0	0
Current period recoveries	0	0	0	0
Current period, net charge offs	0	0	0	0
Year Three
Total	207,382		207,382		198,061
Current period charge-offs	0	0	0	0
Current period recoveries	0	0	0	0
Current period, net charge offs	0	0	0	0
Year Four
Total	201,521		201,521		257,223
Current period charge-offs	0	0	0	0
Current period recoveries	0	0	0	0
Current period, net charge offs	0	0	0	0
Year Five
Total	241,553		241,553		234,781
Current period charge-offs	0	0	0	0
Current period recoveries	0	0	0	0
Current period, net charge offs	0	0	0	0
Prior
Total	1,158,061		1,158,061		1,080,466
Current period charge-offs	0	0	0	0
Current period recoveries	0	0	0	0
Current period, net charge offs	0	0	0	0
Revolving Loans - Amortized Cost Basis
Total	238,356		238,356		226,203
Current period charge-offs	0	0	0	0
Current period recoveries	0	0	0	0
Current period, net charge offs	0	0	0	0
Total
Current period charge-offs	0	0	0	0
Current period recoveries	0	0	0	0
Current period, net charge offs	0	0	0	0
Total	2,667,610		2,667,610		2,404,743
LTSPCs and Farmer Mac Guaranteed Securities | Acceptable | Farm & Ranch
Year One
Total	306,664		306,664		178,213
Year Two
Total	309,938		309,938		213,620
Year Three
Total	206,652		206,652		183,948
Year Four
Total	189,643		189,643		237,042
Year Five
Total	225,421		225,421		207,296
Prior
Total	1,054,049		1,054,049		969,860
Revolving Loans - Amortized Cost Basis
Total	228,509		228,509		211,620
Total
Total	2,520,876		2,520,876		2,201,599
LTSPCs and Farmer Mac Guaranteed Securities | Special mention | Farm & Ranch
Year One
Total	0		0		3,920
Year Two
Total	3,915		3,915		1,742
Year Three
Total	0		0		1,502
Year Four
Total	1,382		1,382		5,603
Year Five
Total	3,190		3,190		19,644
Prior
Total	58,112		58,112		50,004
Revolving Loans - Amortized Cost Basis
Total	6,058		6,058		10,058
Total
Total	72,657		72,657		92,473
LTSPCs and Farmer Mac Guaranteed Securities | Substandard | Farm & Ranch
Year One
Total	0		0		264
Year Two
Total	220		220		10,250
Year Three
Total	730		730		12,611
Year Four
Total	10,496		10,496		14,578
Year Five
Total	12,942		12,942		7,841
Prior
Total	45,900		45,900		60,602
Revolving Loans - Amortized Cost Basis
Total	3,789		3,789		4,525
Total
Total	74,077		74,077		110,671
LTSPCs | Rural Utilities
Year One
Total	0		0		0
Current period charge-offs	0	0	0	0
Current period recoveries	0	0	0	0
Current period, net charge offs	0	0	0	0
Year Two
Total	0		0		0
Current period charge-offs	0	0	0	0
Current period recoveries	0	0	0	0
Current period, net charge offs	0	0	0	0
Year Three
Total	0		0		0
Current period charge-offs	0	0	0	0
Current period recoveries	0	0	0	0
Current period, net charge offs	0	0	0	0
Year Four
Total	0		0		0
Current period charge-offs	0	0	0	0
Current period recoveries	0	0	0	0
Current period, net charge offs	0	0	0	0
Year Five
Total	0		0		0
Current period charge-offs	0	0	0	0
Current period recoveries	0	0	0	0
Current period, net charge offs	0	0	0	0
Prior
Total	511,743		511,743		549,405
Current period charge-offs	0	0	0	0
Current period recoveries	0	0	0	0
Current period, net charge offs	0	0	0	0
Revolving Loans - Amortized Cost Basis
Total	62,512		62,512		7,020
Current period charge-offs	0	0	0	0
Current period recoveries	0	0	0	0
Current period, net charge offs	0	0	0	0
Total
Current period charge-offs	0	0	0	0
Current period recoveries	0	0	0	0
Current period, net charge offs	0	$ 0	0	$ 0
Total	574,255		574,255		556,425
LTSPCs | Acceptable | Rural Utilities
Year One
Total	0		0		0
Year Two
Total	0		0		0
Year Three
Total	0		0		0
Year Four
Total	0		0		0
Year Five
Total	0		0		0
Prior
Total	511,743		511,743		549,405
Revolving Loans - Amortized Cost Basis
Total	62,512		62,512		7,020
Total
Total	574,255		574,255		556,425
LTSPCs | Special mention | Rural Utilities
Year One
Total	0		0		0
Year Two
Total	0		0		0
Year Three
Total	0		0		0
Year Four
Total	0		0		0
Year Five
Total	0		0		0
Prior
Total	0		0		0
Revolving Loans - Amortized Cost Basis
Total	0		0		0
Total
Total	0		0		0
LTSPCs | Substandard | Rural Utilities
Year One
Total	0		0		0
Year Two
Total	0		0		0
Year Three
Total	0		0		0
Year Four
Total	0		0		0
Year Five
Total	0		0		0
Prior
Total	0		0		0
Revolving Loans - Amortized Cost Basis
Total	0		0		0
Total
Total	$ 0		$ 0		$ 0