DOCUMENT AND ENTITY INFORMATION DOCUMENT AND ENTITY INFORMATION - USD ($)	12 Months Ended
	Dec. 31, 2018	Feb. 01, 2019	Jun. 30, 2018
Entity Information [Line Items]
Entity Registrant Name	FEDERAL AGRICULTURAL MORTGAGE CORP
Entity Central Index Key	0000845877
Current Fiscal Year End Date	--12-31
Entity Filer Category	Large Accelerated Filer
Document Type	10-K
Document Period End Date	Dec. 31, 2018
Document Fiscal Year Focus	2018
Document Fiscal Period Focus	Q4
Amendment Flag	false
Trading Symbol	AGM
Entity Well-known Seasoned Issuer	No
Entity Voluntary Filers	No
Entity Current Reporting Status	Yes
Entity Small Business	false
Entity Emerging Growth Company	false
Entity Shell Company	false
Entity Public Float			$ 787,705,568
Common Class A, Voting [Member]
Entity Information [Line Items]
Entity Common Stock, Shares Outstanding		1,030,780
Common Class B, Voting [Member]
Entity Information [Line Items]
Entity Common Stock, Shares Outstanding		500,301
Common Class C, Non-Voting [Member]
Entity Information [Line Items]
Entity Common Stock, Shares Outstanding		9,137,610