Guarantees - Unpaid Principal Balances by Delinquency Status (Details) - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019
Guarantor Obligations [Line Items]
Financing receivable, not past due	$ 8,315,566
Financing receivables, past due	6,286
Total	7,261,933	$ 5,390,977
30-59 Days
Guarantor Obligations [Line Items]
Financing receivables, past due	4,582
60-89 Days
Guarantor Obligations [Line Items]
Financing receivables, past due	632
90 Days and Greater
Guarantor Obligations [Line Items]
Financing receivables, past due	1,072
Farm & Ranch
Guarantor Obligations [Line Items]
Financing receivable, not past due	6,055,154
Financing receivables, past due	6,286
Total	6,176,438
Farm & Ranch | 30-59 Days
Guarantor Obligations [Line Items]
Financing receivables, past due	4,582
Farm & Ranch | 60-89 Days
Guarantor Obligations [Line Items]
Financing receivables, past due	632
Farm & Ranch | 90 Days and Greater
Guarantor Obligations [Line Items]
Financing receivables, past due	1,072	$ 57,719
Farm & Ranch | 90 Days and Greater | Payment Deferral, CARES Act
Guarantor Obligations [Line Items]
Financing receivables, past due	145,500
Rural Utilities:
Guarantor Obligations [Line Items]
Financing receivable, not past due	2,260,412
Financing receivables, past due	0
Total	2,260,412
Rural Utilities: | 30-59 Days
Guarantor Obligations [Line Items]
Financing receivables, past due	0
Rural Utilities: | 60-89 Days
Guarantor Obligations [Line Items]
Financing receivables, past due	0
Rural Utilities: | 90 Days and Greater
Guarantor Obligations [Line Items]
Financing receivables, past due	0
LTSPCs and Farmer Mac Guaranteed Securities | Farm & Ranch
Guarantor Obligations [Line Items]
Financing receivable, not past due	2,389,777
Financing receivables, past due	14,966
Total	2,404,743
LTSPCs and Farmer Mac Guaranteed Securities | Farm & Ranch | Payment Deferral, CARES Act
Guarantor Obligations [Line Items]
Financing receivable, not past due	193,700
LTSPCs and Farmer Mac Guaranteed Securities | Farm & Ranch | 30-59 Days
Guarantor Obligations [Line Items]
Financing receivables, past due	2,189
LTSPCs and Farmer Mac Guaranteed Securities | Farm & Ranch | 60-89 Days
Guarantor Obligations [Line Items]
Financing receivables, past due	1,344
LTSPCs and Farmer Mac Guaranteed Securities | Farm & Ranch | 90 Days and Greater
Guarantor Obligations [Line Items]
Financing receivables, past due	11,433
LTSPCs | Rural Utilities:
Guarantor Obligations [Line Items]
Financing receivable, not past due	556,425
Financing receivables, past due	0
Total	556,425
LTSPCs | Rural Utilities: | 30-59 Days
Guarantor Obligations [Line Items]
Financing receivables, past due	0
LTSPCs | Rural Utilities: | 60-89 Days
Guarantor Obligations [Line Items]
Financing receivables, past due	0
LTSPCs | Rural Utilities: | 90 Days and Greater
Guarantor Obligations [Line Items]
Financing receivables, past due	$ 0