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Investment Securities - Unrealized Loss Position (Details) (USD $)
In Thousands, unless otherwise specified
Mar. 31, 2015
position
Dec. 31, 2014
position
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value [Abstract]    
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than Twelve Months, Fair Value $ 928,268us-gaap_AvailableForSaleSecuritiesContinuousUnrealizedLossPositionLessThanTwelveMonthsFairValue $ 495,501us-gaap_AvailableForSaleSecuritiesContinuousUnrealizedLossPositionLessThanTwelveMonthsFairValue
Available-for-sale Securities, Continuous Unrealized Loss Position, Twelve Months or Longer, Fair Value 232,406us-gaap_AvailableForSaleSecuritiesContinuousUnrealizedLossPositionTwelveMonthsOrLongerFairValue 183,763us-gaap_AvailableForSaleSecuritiesContinuousUnrealizedLossPositionTwelveMonthsOrLongerFairValue
Available-for-sale Securities, Continuous Unrealized Loss Position, Aggregate Loss [Abstract]    
Available-for-Sale Continuous Unrealized Loss Position Less than 12 Months, Aggregate Losses (441)us-gaap_AvailableForSaleSecuritiesContinuousUnrealizedLossPositionLessThan12MonthsAccumulatedLoss (228)us-gaap_AvailableForSaleSecuritiesContinuousUnrealizedLossPositionLessThan12MonthsAccumulatedLoss
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Aggregate Losses (10,805)us-gaap_AvailableForSaleSecuritiesContinuousUnrealizedLossPosition12MonthsOrLongerAccumulatedLoss (9,983)us-gaap_AvailableForSaleSecuritiesContinuousUnrealizedLossPosition12MonthsOrLongerAccumulatedLoss
Available-for-sale Securities, Continuous Unrealized Loss Position, Qualitative Disclosure [Abstract]    
Available-for-sale, Securities in Unrealized Loss Positions, Qualitative Disclosure, Number of Positions 44us-gaap_AvailableforsaleSecuritiesInUnrealizedLossPositionsQualitativeDisclosureNumberOfPositions1 35us-gaap_AvailableforsaleSecuritiesInUnrealizedLossPositionsQualitativeDisclosureNumberOfPositions1
Investment Securities [Member]    
Available-for-sale Securities, Continuous Unrealized Loss Position, Qualitative Disclosure [Abstract]    
Available-for-sale securities in a loss position for more than 12 months, qualitative disclosure, percent of amortized cost 96.00%agm_AvailableForSaleSecuritiesInLossPositionForMoreThan12MonthsQualitativeDisclosurePercentOfAmortizedCost
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_DebtSecuritiesMember		  
Available-for-sale, Securities in Unrealized Loss Positions, Qualitative Disclosure, Number of Positions, Greater than or Equal to One Year 17us-gaap_AvailableforsaleSecuritiesInUnrealizedLossPositionsQualitativeDisclosureNumberOfPositionsGreaterThanOrEqualToOneYear
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_DebtSecuritiesMember		 15us-gaap_AvailableforsaleSecuritiesInUnrealizedLossPositionsQualitativeDisclosureNumberOfPositionsGreaterThanOrEqualToOneYear
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_DebtSecuritiesMember
Standard & Poor's, A- Rating [Member]    
Available-for-sale Securities, Continuous Unrealized Loss Position, Qualitative Disclosure [Abstract]    
Available-for-sale, Securities in Unrealized Loss Positions, Qualitative Disclosure, Number of Positions 1us-gaap_AvailableforsaleSecuritiesInUnrealizedLossPositionsQualitativeDisclosureNumberOfPositions1
/ us-gaap_CreditRatingStandardPoorsAxis
= us-gaap_StandardPoorsAMinusRatingMember		  
Floating Interest Rate [Member] | Floating rate auction-rate certificates backed by Government guaranteed student loans    
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value [Abstract]    
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than Twelve Months, Fair Value 0us-gaap_AvailableForSaleSecuritiesContinuousUnrealizedLossPositionLessThanTwelveMonthsFairValue
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_AuctionRateSecuritiesMember
/ us-gaap_ProductOrServiceAxis
= agm_FloatingInterestRateMember		 0us-gaap_AvailableForSaleSecuritiesContinuousUnrealizedLossPositionLessThanTwelveMonthsFairValue
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_AuctionRateSecuritiesMember
/ us-gaap_ProductOrServiceAxis
= agm_FloatingInterestRateMember
Available-for-sale Securities, Continuous Unrealized Loss Position, Twelve Months or Longer, Fair Value 40,379us-gaap_AvailableForSaleSecuritiesContinuousUnrealizedLossPositionTwelveMonthsOrLongerFairValue
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_AuctionRateSecuritiesMember
/ us-gaap_ProductOrServiceAxis
= agm_FloatingInterestRateMember		 40,576us-gaap_AvailableForSaleSecuritiesContinuousUnrealizedLossPositionTwelveMonthsOrLongerFairValue
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_AuctionRateSecuritiesMember
/ us-gaap_ProductOrServiceAxis
= agm_FloatingInterestRateMember
Available-for-sale Securities, Continuous Unrealized Loss Position, Aggregate Loss [Abstract]    
Available-for-Sale Continuous Unrealized Loss Position Less than 12 Months, Aggregate Losses 0us-gaap_AvailableForSaleSecuritiesContinuousUnrealizedLossPositionLessThan12MonthsAccumulatedLoss
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_AuctionRateSecuritiesMember
/ us-gaap_ProductOrServiceAxis
= agm_FloatingInterestRateMember		 0us-gaap_AvailableForSaleSecuritiesContinuousUnrealizedLossPositionLessThan12MonthsAccumulatedLoss
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_AuctionRateSecuritiesMember
/ us-gaap_ProductOrServiceAxis
= agm_FloatingInterestRateMember
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Aggregate Losses (6,221)us-gaap_AvailableForSaleSecuritiesContinuousUnrealizedLossPosition12MonthsOrLongerAccumulatedLoss
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_AuctionRateSecuritiesMember
/ us-gaap_ProductOrServiceAxis
= agm_FloatingInterestRateMember		 (6,024)us-gaap_AvailableForSaleSecuritiesContinuousUnrealizedLossPosition12MonthsOrLongerAccumulatedLoss
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_AuctionRateSecuritiesMember
/ us-gaap_ProductOrServiceAxis
= agm_FloatingInterestRateMember
Floating Interest Rate [Member] | Asset-backed Securities [Member]    
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value [Abstract]    
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than Twelve Months, Fair Value 22,971us-gaap_AvailableForSaleSecuritiesContinuousUnrealizedLossPositionLessThanTwelveMonthsFairValue
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_AssetBackedSecuritiesMember
/ us-gaap_ProductOrServiceAxis
= agm_FloatingInterestRateMember		 19,388us-gaap_AvailableForSaleSecuritiesContinuousUnrealizedLossPositionLessThanTwelveMonthsFairValue
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_AssetBackedSecuritiesMember
/ us-gaap_ProductOrServiceAxis
= agm_FloatingInterestRateMember
Available-for-sale Securities, Continuous Unrealized Loss Position, Twelve Months or Longer, Fair Value 640us-gaap_AvailableForSaleSecuritiesContinuousUnrealizedLossPositionTwelveMonthsOrLongerFairValue
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_AssetBackedSecuritiesMember
/ us-gaap_ProductOrServiceAxis
= agm_FloatingInterestRateMember		 0us-gaap_AvailableForSaleSecuritiesContinuousUnrealizedLossPositionTwelveMonthsOrLongerFairValue
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_AssetBackedSecuritiesMember
/ us-gaap_ProductOrServiceAxis
= agm_FloatingInterestRateMember
Available-for-sale Securities, Continuous Unrealized Loss Position, Aggregate Loss [Abstract]    
Available-for-Sale Continuous Unrealized Loss Position Less than 12 Months, Aggregate Losses (46)us-gaap_AvailableForSaleSecuritiesContinuousUnrealizedLossPositionLessThan12MonthsAccumulatedLoss
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_AssetBackedSecuritiesMember
/ us-gaap_ProductOrServiceAxis
= agm_FloatingInterestRateMember		 (37)us-gaap_AvailableForSaleSecuritiesContinuousUnrealizedLossPositionLessThan12MonthsAccumulatedLoss
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_AssetBackedSecuritiesMember
/ us-gaap_ProductOrServiceAxis
= agm_FloatingInterestRateMember
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Aggregate Losses 0us-gaap_AvailableForSaleSecuritiesContinuousUnrealizedLossPosition12MonthsOrLongerAccumulatedLoss
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_AssetBackedSecuritiesMember
/ us-gaap_ProductOrServiceAxis
= agm_FloatingInterestRateMember		 0us-gaap_AvailableForSaleSecuritiesContinuousUnrealizedLossPosition12MonthsOrLongerAccumulatedLoss
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_AssetBackedSecuritiesMember
/ us-gaap_ProductOrServiceAxis
= agm_FloatingInterestRateMember
Floating Interest Rate [Member] | Government/GSE Guaranteed Mortgage Backed Securities [Member]    
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value [Abstract]    
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than Twelve Months, Fair Value 121,071us-gaap_AvailableForSaleSecuritiesContinuousUnrealizedLossPositionLessThanTwelveMonthsFairValue
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_MortgageBackedSecuritiesMember
/ us-gaap_ProductOrServiceAxis
= agm_FloatingInterestRateMember		 76,100us-gaap_AvailableForSaleSecuritiesContinuousUnrealizedLossPositionLessThanTwelveMonthsFairValue
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_MortgageBackedSecuritiesMember
/ us-gaap_ProductOrServiceAxis
= agm_FloatingInterestRateMember
Available-for-sale Securities, Continuous Unrealized Loss Position, Twelve Months or Longer, Fair Value 125,546us-gaap_AvailableForSaleSecuritiesContinuousUnrealizedLossPositionTwelveMonthsOrLongerFairValue
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_MortgageBackedSecuritiesMember
/ us-gaap_ProductOrServiceAxis
= agm_FloatingInterestRateMember		 76,867us-gaap_AvailableForSaleSecuritiesContinuousUnrealizedLossPositionTwelveMonthsOrLongerFairValue
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_MortgageBackedSecuritiesMember
/ us-gaap_ProductOrServiceAxis
= agm_FloatingInterestRateMember
Available-for-sale Securities, Continuous Unrealized Loss Position, Aggregate Loss [Abstract]    
Available-for-Sale Continuous Unrealized Loss Position Less than 12 Months, Aggregate Losses (244)us-gaap_AvailableForSaleSecuritiesContinuousUnrealizedLossPositionLessThan12MonthsAccumulatedLoss
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_MortgageBackedSecuritiesMember
/ us-gaap_ProductOrServiceAxis
= agm_FloatingInterestRateMember		 (164)us-gaap_AvailableForSaleSecuritiesContinuousUnrealizedLossPositionLessThan12MonthsAccumulatedLoss
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_MortgageBackedSecuritiesMember
/ us-gaap_ProductOrServiceAxis
= agm_FloatingInterestRateMember
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Aggregate Losses (425)us-gaap_AvailableForSaleSecuritiesContinuousUnrealizedLossPosition12MonthsOrLongerAccumulatedLoss
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_MortgageBackedSecuritiesMember
/ us-gaap_ProductOrServiceAxis
= agm_FloatingInterestRateMember		 (279)us-gaap_AvailableForSaleSecuritiesContinuousUnrealizedLossPosition12MonthsOrLongerAccumulatedLoss
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_MortgageBackedSecuritiesMember
/ us-gaap_ProductOrServiceAxis
= agm_FloatingInterestRateMember
Floating Interest Rate [Member] | GSE Subordinated Debt [Member}    
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value [Abstract]    
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than Twelve Months, Fair Value 0us-gaap_AvailableForSaleSecuritiesContinuousUnrealizedLossPositionLessThanTwelveMonthsFairValue
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_SubordinatedDebtMember
/ us-gaap_ProductOrServiceAxis
= agm_FloatingInterestRateMember		 0us-gaap_AvailableForSaleSecuritiesContinuousUnrealizedLossPositionLessThanTwelveMonthsFairValue
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_SubordinatedDebtMember
/ us-gaap_ProductOrServiceAxis
= agm_FloatingInterestRateMember
Available-for-sale Securities, Continuous Unrealized Loss Position, Twelve Months or Longer, Fair Value 65,841us-gaap_AvailableForSaleSecuritiesContinuousUnrealizedLossPositionTwelveMonthsOrLongerFairValue
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_SubordinatedDebtMember
/ us-gaap_ProductOrServiceAxis
= agm_FloatingInterestRateMember		 66,320us-gaap_AvailableForSaleSecuritiesContinuousUnrealizedLossPositionTwelveMonthsOrLongerFairValue
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_SubordinatedDebtMember
/ us-gaap_ProductOrServiceAxis
= agm_FloatingInterestRateMember
Available-for-sale Securities, Continuous Unrealized Loss Position, Aggregate Loss [Abstract]    
Available-for-Sale Continuous Unrealized Loss Position Less than 12 Months, Aggregate Losses 0us-gaap_AvailableForSaleSecuritiesContinuousUnrealizedLossPositionLessThan12MonthsAccumulatedLoss
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_SubordinatedDebtMember
/ us-gaap_ProductOrServiceAxis
= agm_FloatingInterestRateMember		 0us-gaap_AvailableForSaleSecuritiesContinuousUnrealizedLossPositionLessThan12MonthsAccumulatedLoss
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_SubordinatedDebtMember
/ us-gaap_ProductOrServiceAxis
= agm_FloatingInterestRateMember
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Aggregate Losses (4,159)us-gaap_AvailableForSaleSecuritiesContinuousUnrealizedLossPosition12MonthsOrLongerAccumulatedLoss
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_SubordinatedDebtMember
/ us-gaap_ProductOrServiceAxis
= agm_FloatingInterestRateMember		 (3,680)us-gaap_AvailableForSaleSecuritiesContinuousUnrealizedLossPosition12MonthsOrLongerAccumulatedLoss
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_SubordinatedDebtMember
/ us-gaap_ProductOrServiceAxis
= agm_FloatingInterestRateMember
Floating Interest Rate [Member] | US Treasury Securities [Member]    
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value [Abstract]    
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than Twelve Months, Fair Value   74,980us-gaap_AvailableForSaleSecuritiesContinuousUnrealizedLossPositionLessThanTwelveMonthsFairValue
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_USTreasurySecuritiesMember
/ us-gaap_ProductOrServiceAxis
= agm_FloatingInterestRateMember
Available-for-sale Securities, Continuous Unrealized Loss Position, Twelve Months or Longer, Fair Value   0us-gaap_AvailableForSaleSecuritiesContinuousUnrealizedLossPositionTwelveMonthsOrLongerFairValue
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_USTreasurySecuritiesMember
/ us-gaap_ProductOrServiceAxis
= agm_FloatingInterestRateMember
Available-for-sale Securities, Continuous Unrealized Loss Position, Aggregate Loss [Abstract]    
Available-for-Sale Continuous Unrealized Loss Position Less than 12 Months, Aggregate Losses   (11)us-gaap_AvailableForSaleSecuritiesContinuousUnrealizedLossPositionLessThan12MonthsAccumulatedLoss
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_USTreasurySecuritiesMember
/ us-gaap_ProductOrServiceAxis
= agm_FloatingInterestRateMember
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Aggregate Losses   0us-gaap_AvailableForSaleSecuritiesContinuousUnrealizedLossPosition12MonthsOrLongerAccumulatedLoss
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_USTreasurySecuritiesMember
/ us-gaap_ProductOrServiceAxis
= agm_FloatingInterestRateMember
Fixed Interest Rate [Member] | USDA Securities [Member]    
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value [Abstract]    
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than Twelve Months, Fair Value 121,950us-gaap_AvailableForSaleSecuritiesContinuousUnrealizedLossPositionLessThanTwelveMonthsFairValue
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_USGovernmentAgenciesDebtSecuritiesMember
/ us-gaap_ProductOrServiceAxis
= agm_FixedInterestRateMember		  
Available-for-sale Securities, Continuous Unrealized Loss Position, Twelve Months or Longer, Fair Value 0us-gaap_AvailableForSaleSecuritiesContinuousUnrealizedLossPositionTwelveMonthsOrLongerFairValue
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_USGovernmentAgenciesDebtSecuritiesMember
/ us-gaap_ProductOrServiceAxis
= agm_FixedInterestRateMember		  
Available-for-sale Securities, Continuous Unrealized Loss Position, Aggregate Loss [Abstract]    
Available-for-Sale Continuous Unrealized Loss Position Less than 12 Months, Aggregate Losses (68)us-gaap_AvailableForSaleSecuritiesContinuousUnrealizedLossPositionLessThan12MonthsAccumulatedLoss
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_USGovernmentAgenciesDebtSecuritiesMember
/ us-gaap_ProductOrServiceAxis
= agm_FixedInterestRateMember		  
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Aggregate Losses 0us-gaap_AvailableForSaleSecuritiesContinuousUnrealizedLossPosition12MonthsOrLongerAccumulatedLoss
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_USGovernmentAgenciesDebtSecuritiesMember
/ us-gaap_ProductOrServiceAxis
= agm_FixedInterestRateMember		  
Fixed Interest Rate [Member] | US Treasury Securities [Member]    
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value [Abstract]    
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than Twelve Months, Fair Value 662,276us-gaap_AvailableForSaleSecuritiesContinuousUnrealizedLossPositionLessThanTwelveMonthsFairValue
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_USTreasurySecuritiesMember
/ us-gaap_ProductOrServiceAxis
= agm_FixedInterestRateMember		 325,033us-gaap_AvailableForSaleSecuritiesContinuousUnrealizedLossPositionLessThanTwelveMonthsFairValue
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_USTreasurySecuritiesMember
/ us-gaap_ProductOrServiceAxis
= agm_FixedInterestRateMember
Available-for-sale Securities, Continuous Unrealized Loss Position, Twelve Months or Longer, Fair Value 0us-gaap_AvailableForSaleSecuritiesContinuousUnrealizedLossPositionTwelveMonthsOrLongerFairValue
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_USTreasurySecuritiesMember
/ us-gaap_ProductOrServiceAxis
= agm_FixedInterestRateMember		 0us-gaap_AvailableForSaleSecuritiesContinuousUnrealizedLossPositionTwelveMonthsOrLongerFairValue
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_USTreasurySecuritiesMember
/ us-gaap_ProductOrServiceAxis
= agm_FixedInterestRateMember
Available-for-sale Securities, Continuous Unrealized Loss Position, Aggregate Loss [Abstract]    
Available-for-Sale Continuous Unrealized Loss Position Less than 12 Months, Aggregate Losses (83)us-gaap_AvailableForSaleSecuritiesContinuousUnrealizedLossPositionLessThan12MonthsAccumulatedLoss
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_USTreasurySecuritiesMember
/ us-gaap_ProductOrServiceAxis
= agm_FixedInterestRateMember		 (16)us-gaap_AvailableForSaleSecuritiesContinuousUnrealizedLossPositionLessThan12MonthsAccumulatedLoss
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_USTreasurySecuritiesMember
/ us-gaap_ProductOrServiceAxis
= agm_FixedInterestRateMember
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Aggregate Losses $ 0us-gaap_AvailableForSaleSecuritiesContinuousUnrealizedLossPosition12MonthsOrLongerAccumulatedLoss
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_USTreasurySecuritiesMember
/ us-gaap_ProductOrServiceAxis
= agm_FixedInterestRateMember		 $ 0us-gaap_AvailableForSaleSecuritiesContinuousUnrealizedLossPosition12MonthsOrLongerAccumulatedLoss
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_USTreasurySecuritiesMember
/ us-gaap_ProductOrServiceAxis
= agm_FixedInterestRateMember