Guarantees - Credit Quality Indicators (Details) - USD ($) $ in Thousands	3 Months Ended		12 Months Ended
	Mar. 31, 2021	Mar. 31, 2020	Dec. 31, 2020
Total
Total	$ 7,341,912		$ 7,261,933
Total	7,341,912		7,261,933
Financing receivables, past due	19,144		6,286
Rural Utilities
2021
Total	10,979		667,489
Current period charge-offs	0		0
Current period recoveries	0		0
Current period Farm & Ranch net charge-offs	0		0
2020
Total	663,330		809,921
Current period charge-offs	0		0
Financing Receivable, Originated in Fiscal Year before Latest Fiscal Year, Allowance for Credit Loss, Recovery	0		0
Financing Receivable, Originated in Fiscal Year before Latest Fiscal Year, Allowance for Credit Loss, Writeoff, After Recovery	0		0
2019
Total	801,799		8,260
Current period charge-offs	0		0
Financing Receivable, Originated Two Years before Latest Fiscal Year, Allowance for Credit Loss, Recovery	0		0
Financing Receivable, Originated Two Years before Latest Fiscal Year, Allowance for Credit Loss, Writeoff, After Recovery	0		0
2018
Total	8,181		89,842
Current period charge-offs	0		0
Financing Receivable, Originated Three Years before Latest Fiscal Year, Allowance for Credit Loss, Recovery	0		0
Financing Receivable, Originated Three Years before Latest Fiscal Year, Allowance for Credit Loss, Writeoff, After Recovery	0		0
2017
Total	89,621		31,275
Current period charge-offs	0		0
Financing Receivable, Originated Four Years before Latest Fiscal Year, Allowance for Credit Loss, Recovery	0		0
Financing Receivable, Originated Four Years before Latest Fiscal Year, Allowance for Credit Loss, Writeoff, After Recovery	0		0
Prior
Total	650,486		641,145
Current period charge-offs	0		0
Financing Receivable, Originated Five or More Years before Latest Fiscal Year, Allowance for Credit Loss, Recovery	0		0
Financing Receivable, Originated Five or More Years before Latest Fiscal Year, Allowance for Credit Loss, Writeoff, After Recovery	0		0
Revolving Loans - Amortized Cost Basis
Total	22,708		12,480
Current period charge-offs	0		0
Financing Receivable, Revolving, Allowance for Credit Loss, Recovery	0		0
Financing Receivable, Revolving, Allowance for Credit Loss, Writeoff, After Recovery	0		0
Total
Total	2,247,104		2,260,412
Current period charge-offs	0		0
Financing Receivable, Allowance for Credit Loss, Recovery	0		0
Financing Receivable, Allowance for Credit Loss, Writeoff, after Recovery	0	$ 0	0
Total	2,247,104		2,260,412
Financing receivables, past due	0		0
Farm & Ranch
2021
Total	558,717		2,021,189
Current period charge-offs	0		0
Current period recoveries	0		0
Current period Farm & Ranch net charge-offs	0		0
2020
Total	2,029,701		859,880
Current period charge-offs	0		0
Financing Receivable, Originated in Fiscal Year before Latest Fiscal Year, Allowance for Credit Loss, Recovery	0		0
Financing Receivable, Originated in Fiscal Year before Latest Fiscal Year, Allowance for Credit Loss, Writeoff, After Recovery	0		0
2019
Total	805,952		524,541
Current period charge-offs	0		0
Financing Receivable, Originated Two Years before Latest Fiscal Year, Allowance for Credit Loss, Recovery	0		0
Financing Receivable, Originated Two Years before Latest Fiscal Year, Allowance for Credit Loss, Writeoff, After Recovery	0		0
2018
Total	489,046		562,007
Current period charge-offs	0		0
Financing Receivable, Originated Three Years before Latest Fiscal Year, Allowance for Credit Loss, Recovery	0		0
Financing Receivable, Originated Three Years before Latest Fiscal Year, Allowance for Credit Loss, Writeoff, After Recovery	0		0
2017
Total	460,291		515,561
Current period charge-offs	0		0
Financing Receivable, Originated Four Years before Latest Fiscal Year, Allowance for Credit Loss, Recovery	0		0
Financing Receivable, Originated Four Years before Latest Fiscal Year, Allowance for Credit Loss, Writeoff, After Recovery	0		0
Prior
Total	1,452,339		1,140,603
Current period charge-offs	0		0
Financing Receivable, Originated Five or More Years before Latest Fiscal Year, Allowance for Credit Loss, Recovery	0		0
Financing Receivable, Originated Five or More Years before Latest Fiscal Year, Allowance for Credit Loss, Writeoff, After Recovery	0		0
Revolving Loans - Amortized Cost Basis
Total	506,921		552,657
Current period charge-offs	0		0
Financing Receivable, Revolving, Allowance for Credit Loss, Recovery	0		0
Financing Receivable, Revolving, Allowance for Credit Loss, Writeoff, After Recovery	0		0
Total
Total	6,302,967		6,176,438
Current period charge-offs	0		0
Financing Receivable, Allowance for Credit Loss, Recovery	0		0
Financing Receivable, Allowance for Credit Loss, Writeoff, after Recovery	0	0	0
Total	6,302,967		6,176,438
Financing receivables, past due	19,144		6,286
Acceptable | Rural Utilities
2021
Total	10,979		667,489
2020
Total	639,730		809,921
2019
Total	801,799		8,260
2018
Total	8,181		89,842
2017
Total	89,621		31,275
Prior
Total	650,486		641,145
Revolving Loans - Amortized Cost Basis
Total	22,708		12,480
Total
Total	2,223,504		2,260,412
Total	2,223,504		2,260,412
Acceptable | Farm & Ranch
2021
Total	542,638		1,947,618
2020
Total	1,923,390		774,315
2019
Total	724,202		484,345
2018
Total	443,929		500,768
2017
Total	399,931		465,277
Prior
Total	1,334,771		1,068,693
Revolving Loans - Amortized Cost Basis
Total	482,993		535,742
Total
Total	5,851,854		5,776,758
Total	5,851,854		5,776,758
Special mention | Rural Utilities
2021
Total	0		0
2020
Total	23,600		0
2019
Total	0		0
2018
Total	0		0
2017
Total	0		0
Prior
Total	0		0
Revolving Loans - Amortized Cost Basis
Total	0		0
Total
Total	23,600		0
Total	23,600		0
Special mention | Farm & Ranch
2021
Total	16,079		70,171
2020
Total	102,656		79,744
2019
Total	56,723		18,317
2018
Total	16,292		8,530
2017
Total	2,569		13,111
Prior
Total	23,003		21,328
Revolving Loans - Amortized Cost Basis
Total	11,804		7,656
Total
Total	229,126		218,857
Total	229,126		218,857
Substandard | Rural Utilities
2021
Total	0		0
2020
Total	0		0
2019
Total	0		0
2018
Total	0		0
2017
Total	0		0
Prior
Total	0		0
Revolving Loans - Amortized Cost Basis
Total	0		0
Total
Total	0		0
Total	0		0
Substandard | Farm & Ranch
2021
Total	0		3,400
2020
Total	3,655		5,821
2019
Total	25,027		21,879
2018
Total	28,825		52,709
2017
Total	57,791		37,173
Prior
Total	94,565		50,582
Revolving Loans - Amortized Cost Basis
Total	12,124		9,259
Total
Total	221,987		180,823
Total	221,987		180,823
LTSPCs and Farmer Mac Guaranteed Securities | Rural Utilities
2021
Total	0		0
Current period charge-offs	0	0
Current period recoveries	0	0
Current period Farm & Ranch net charge-offs	0	0
2020
Total	0		0
Current period charge-offs	0	0
Financing Receivable, Originated in Fiscal Year before Latest Fiscal Year, Allowance for Credit Loss, Recovery	0	0
Financing Receivable, Originated in Fiscal Year before Latest Fiscal Year, Allowance for Credit Loss, Writeoff, After Recovery	0	0
2019
Total	0		0
Current period charge-offs	0	0
Financing Receivable, Originated Two Years before Latest Fiscal Year, Allowance for Credit Loss, Recovery	0	0
Financing Receivable, Originated Two Years before Latest Fiscal Year, Allowance for Credit Loss, Writeoff, After Recovery	0	0
2018
Total	0		0
Current period charge-offs	0	0
Financing Receivable, Originated Three Years before Latest Fiscal Year, Allowance for Credit Loss, Recovery	0	0
Financing Receivable, Originated Three Years before Latest Fiscal Year, Allowance for Credit Loss, Writeoff, After Recovery	0	0
2017
Total	0		0
Current period charge-offs	0	0
Financing Receivable, Originated Four Years before Latest Fiscal Year, Allowance for Credit Loss, Recovery	0	0
Financing Receivable, Originated Four Years before Latest Fiscal Year, Allowance for Credit Loss, Writeoff, After Recovery	0	0
Prior
Total	538,541		549,405
Current period charge-offs	0	0
Financing Receivable, Originated Five or More Years before Latest Fiscal Year, Allowance for Credit Loss, Recovery	0	0
Financing Receivable, Originated Five or More Years before Latest Fiscal Year, Allowance for Credit Loss, Writeoff, After Recovery	0	0
Revolving Loans - Amortized Cost Basis
Total	18,792		7,020
Current period charge-offs	0	0
Financing Receivable, Revolving, Allowance for Credit Loss, Recovery	0	0
Financing Receivable, Revolving, Allowance for Credit Loss, Writeoff, After Recovery	0	0
Total
Total	557,333		556,425
Current period charge-offs	0	0
Financing Receivable, Allowance for Credit Loss, Recovery	0	0
Financing Receivable, Allowance for Credit Loss, Writeoff, after Recovery	0	$ 0
Total	557,333		556,425
LTSPCs and Farmer Mac Guaranteed Securities | Farm & Ranch
2021
Total	83,222		182,397
Current period charge-offs	0		0
Current period recoveries	0		0
Current period Farm & Ranch net charge-offs	0		0
2020
Total	193,946		225,612
Current period charge-offs	0		0
Financing Receivable, Originated in Fiscal Year before Latest Fiscal Year, Allowance for Credit Loss, Recovery	0		0
Financing Receivable, Originated in Fiscal Year before Latest Fiscal Year, Allowance for Credit Loss, Writeoff, After Recovery	0		0
2019
Total	196,288		198,061
Current period charge-offs	0		0
Financing Receivable, Originated Two Years before Latest Fiscal Year, Allowance for Credit Loss, Recovery	0		0
Financing Receivable, Originated Two Years before Latest Fiscal Year, Allowance for Credit Loss, Writeoff, After Recovery	0		0
2018
Total	191,962		257,223
Current period charge-offs	0		0
Financing Receivable, Originated Three Years before Latest Fiscal Year, Allowance for Credit Loss, Recovery	0		0
Financing Receivable, Originated Three Years before Latest Fiscal Year, Allowance for Credit Loss, Writeoff, After Recovery	0		0
2017
Total	236,881		234,781
Current period charge-offs	0		0
Financing Receivable, Originated Four Years before Latest Fiscal Year, Allowance for Credit Loss, Recovery	0		0
Financing Receivable, Originated Four Years before Latest Fiscal Year, Allowance for Credit Loss, Writeoff, After Recovery	0		0
Prior
Total	1,201,958		1,080,466
Current period charge-offs	0		0
Financing Receivable, Originated Five or More Years before Latest Fiscal Year, Allowance for Credit Loss, Recovery	0		0
Financing Receivable, Originated Five or More Years before Latest Fiscal Year, Allowance for Credit Loss, Writeoff, After Recovery	0		0
Revolving Loans - Amortized Cost Basis
Total	222,128		226,203
Current period charge-offs	0		0
Financing Receivable, Revolving, Allowance for Credit Loss, Recovery	0		0
Financing Receivable, Revolving, Allowance for Credit Loss, Writeoff, After Recovery	0		0
Total
Total	2,326,385		2,404,743
Current period charge-offs	0		0
Financing Receivable, Allowance for Credit Loss, Recovery	0		0
Financing Receivable, Allowance for Credit Loss, Writeoff, after Recovery	0		0
Total	2,326,385		2,404,743
Financing receivables, past due	11,142		14,966
LTSPCs and Farmer Mac Guaranteed Securities | Acceptable | Rural Utilities
2021
Total	0		0
2020
Total	0		0
2019
Total	0		0
2018
Total	0		0
2017
Total	0		0
Prior
Total	538,541		549,405
Revolving Loans - Amortized Cost Basis
Total	18,792		7,020
Total
Total	557,333		556,425
Total	557,333		556,425
LTSPCs and Farmer Mac Guaranteed Securities | Acceptable | Farm & Ranch
2021
Total	83,222		178,213
2020
Total	181,684		213,620
2019
Total	193,825		183,948
2018
Total	178,134		237,042
2017
Total	222,030		207,296
Prior
Total	1,071,479		969,860
Revolving Loans - Amortized Cost Basis
Total	205,814		211,620
Total
Total	2,136,188		2,201,599
Total	2,136,188		2,201,599
LTSPCs and Farmer Mac Guaranteed Securities | Special mention | Rural Utilities
2021
Total	0		0
2020
Total	0		0
2019
Total	0		0
2018
Total	0		0
2017
Total	0		0
Prior
Total	0		0
Revolving Loans - Amortized Cost Basis
Total	0		0
Total
Total	0		0
Total	0		0
LTSPCs and Farmer Mac Guaranteed Securities | Special mention | Farm & Ranch
2021
Total	0		3,920
2020
Total	12,020		1,742
2019
Total	1,727		1,502
2018
Total	1,493		5,603
2017
Total	436		19,644
Prior
Total	62,767		50,004
Revolving Loans - Amortized Cost Basis
Total	12,080		10,058
Total
Total	90,523		92,473
Total	90,523		92,473
LTSPCs and Farmer Mac Guaranteed Securities | Substandard | Rural Utilities
2021
Total	0		0
2020
Total	0		0
2019
Total	0		0
2018
Total	0		0
2017
Total	0		0
Prior
Total	0		0
Revolving Loans - Amortized Cost Basis
Total	0		0
Total
Total	0		0
Total	0		0
LTSPCs and Farmer Mac Guaranteed Securities | Substandard | Farm & Ranch
2021
Total	0		264
2020
Total	242		10,250
2019
Total	736		12,611
2018
Total	12,335		14,578
2017
Total	14,415		7,841
Prior
Total	67,712		60,602
Revolving Loans - Amortized Cost Basis
Total	4,234		4,525
Total
Total	99,674		110,671
Total	99,674		110,671
LTSPCs | Rural Utilities
Total
Total	557,333		556,425
Total	557,333		556,425
Financing receivables, past due	0		$ 0
LTSPCs | Acceptable | Rural Utilities
2021
Total	0
2020
Total	0
2019
Total	0
2018
Total	0
2017
Total	0
Prior
Total	538,541
Revolving Loans - Amortized Cost Basis
Total	18,792
LTSPCs | Special mention | Rural Utilities
2021
Total	0
2020
Total	0
2019
Total	0
2018
Total	0
2017
Total	0
Prior
Total	0
Revolving Loans - Amortized Cost Basis
Total	0
LTSPCs | Substandard | Rural Utilities
2021
Total	0
2020
Total	0
2019
Total	0
2018
Total	0
2017
Total	0
Prior
Total	0
Revolving Loans - Amortized Cost Basis
Total	$ 0