Off-Balance Sheet Guarantees and Long Term Standby Purchase Commitments - Narrative (Details) (Collateralized Loan Obligations [Member], USD $)	3 Months Ended	12 Months Ended
	Mar. 31, 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	15,200,000	15,800,000
Long-Term Standby Purchase Commitments [Member]
Long-term Purchase Commitment [Line Items]
Guarantor Obligations, Maximum Exposure, Undiscounted	2,200,000,000	2,200,000,000
Long-Term Standby Purchase Commitments [Member] | Variable Interest Entity, Not Primary Beneficiary [Member]
Long-term Purchase Commitment [Line Items]
Weighted average remaining maturity, Loans underlying guarantees not held by transferor	13 years 8 months 12 days	13 years 7 months 6 days
Long-Term Standby Purchase Commitments On Or After January 1, 2003 [Member]
Long-term Purchase Commitment [Line Items]
Guarantor Obligations, Current Carrying Value	23,700,000	22,000,000
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	13 years 2 months 12 days	13 years 4 months 24 days
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	4 years 2 months 12 days	4 years 8 months 12 days