Off-Balance Sheet Guarantees and Long Term Standby Purchase Commitments - Narrative (Details) (Collateralized Loan Obligations [Member], USD $)	9 Months Ended	12 Months Ended
	Sep. 30, 2013	Dec. 31, 2012
Financial Guarantee [Member] | Variable Interest Entity, Not Primary Beneficiary [Member]
Long-term Purchase Commitment [Line Items]
Guarantor Obligations, Current Carrying Value	$ 14,000,000	$ 15,800,000
Long-Term Standby Purchase Commitments [Member]
Long-term Purchase Commitment [Line Items]
Weighted average remaining maturity, Loans underlying guarantees not held by transferor	13 years 10 months 24 days	13 years 7 months 6 days
Guarantor Obligations, Maximum Exposure, Undiscounted	2,300,000,000	2,200,000,000
Long-Term Standby Purchase Commitments On Or After January 1, 2003 [Member]
Long-term Purchase Commitment [Line Items]
Guarantor Obligations, Current Carrying Value	$ 26,100,000	$ 22,000,000
Off Balance Sheet Farmer Mac Guaranteed Securities [Member] | Financial Guarantee [Member]
Long-term Purchase Commitment [Line Items]
Weighted average remaining maturity, Loans underlying guarantees not held by transferor	12 years 10 months 24 days	13 years 4 months 24 days
Off Balance Sheet Farmer Mac Guaranteed Securities AgVantage [Member] | Financial Guarantee [Member]
Long-term Purchase Commitment [Line Items]
Weighted average remaining maturity, Loans underlying guarantees not held by transferor	3 years 8 months 12 days	4 years 8 months 12 days