Financial Derivatives - Hedged Items in Fair Value Hedging Relationships (Details) - USD ($) $ in Thousands	Jun. 30, 2023	Dec. 31, 2022
Available-for-Sale Securities
HedgedItemsinFairValueHedgingRelationship [Line Items]
Carrying Amount of Hedged Assets/(Liabilities)	$ 1,130,332	$ 876,063
Hedged Asset	(111,648)	(107,107)
Loans
HedgedItemsinFairValueHedgingRelationship [Line Items]
Carrying Amount of Hedged Assets/(Liabilities)	1,701,539	1,623,301
Hedged Asset	(319,702)	(327,278)
Long-term Debt
HedgedItemsinFairValueHedgingRelationship [Line Items]
Carrying Amount of Hedged Assets/(Liabilities)	(12,939,984)	(12,151,382)
Hedged Liability	489,407	531,086
Farmer Mac Guaranteed Securities
HedgedItemsinFairValueHedgingRelationship [Line Items]
Carrying Amount of Hedged Assets/(Liabilities)	5,029,633	4,814,784
Hedged Asset	$ (355,498)	$ (346,873)

[Line Items] for HedgedItemsinFairValueHedgingRelationship [Table]

No definition available.

Name:	agm_HedgedItemsinFairValueHedgingRelationshipLineItems
Namespace Prefix:	agm_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Definition

Amount of hedged item in hedging relationship. Excludes hedged asset or liability.

+ References

No definition available.

+ Details

Name:	us-gaap_DerivativeAmountOfHedgedItem
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	na
Period Type:	instant

- Definition

Amount of cumulative increase (decrease) in fair value of hedged asset in fair value hedge, attributable to hedged risk.

+ References

Reference 1: http://www.xbrl.org/2003/role/exampleRef
-Topic 815
-SubTopic 10
-Name Accounting Standards Codification
-Section 55
-Paragraph 181
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147480401/815-10-55-181

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Topic 815
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 4EE
-Subparagraph (b)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147480434/815-10-50-4EE

+ Details

Name:	us-gaap_HedgedAssetFairValueHedgeCumulativeIncreaseDecrease
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Amount of cumulative increase (decrease) in fair value of hedged liability in fair value hedge, attributable to hedged risk.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Topic 815
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 4EE
-Subparagraph (b)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147480434/815-10-50-4EE

+ Details

Name:	us-gaap_HedgedLiabilityFairValueHedgeCumulativeIncreaseDecrease
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Details

Name:	us-gaap_BalanceSheetLocationAxis=agm_DebtSecuritiesAvailableForSaleMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_BalanceSheetLocationAxis=us-gaap_LoansMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_BalanceSheetLocationAxis=us-gaap_LongTermDebtMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FinancialInstrumentAxis=us-gaap_MortgageBackedSecuritiesIssuedByUSGovernmentSponsoredEnterprisesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type: