Earnings (Loss) Per Share (Details) (USD $)	3 Months Ended				6 Months Ended
	Jun. 30, 2014		Jun. 30, 2013		Jun. 30, 2014		Jun. 30, 2013
Earnings Per Share [Abstract]
Net Income, Including Portion Attributable to Noncontrolling Interest	$ 3,667,000,000		$ 10,095,000,000	[1]	$ 8,992,000,000		$ 68,780,000,000	[1]
Net Income Attributable to Noncontrolling Interest	(1,000,000)		(11,000,000)	[1]	(1,000,000)		(11,000,000)	[1]
Net income attributable to Fannie Mae	3,666,000,000		10,084,000,000	[1]	8,991,000,000		68,769,000,000	[1]
Dividends distributed or available for distribution to senior preferred stockholder	(3,712,000,000)	[2]	(10,243,000,000)	[2]	(9,404,000,000)	[2]	(69,611,000,000)	[2]
Net loss attributable to common stockholders	(46,000,000)		(159,000,000)		(413,000,000)		(842,000,000)
Weighted-average common shares outstanding: basic and diluted	5,762,000,000	[3]	5,762,000,000	[3]	5,762,000,000	[3]	5,762,000,000	[3]
Loss per share: basic and diluted	$ (0.01)		$ (0.03)		$ (0.07)		$ (0.15)
Capital Reserve Amount, current year, Senior Preferred Stock Purchase Agreement, Amendment	2,400,000,000				2,400,000,000
Capital Reserve Amount, prior year, Senior Preferred Stock Purchase Agreement Amendment			$ 3,000,000,000				$ 3,000,000,000
Weighted-average shares of common stock that would be issued upon the full exercise of the warrant issued to Treasury	4,600,000,000		4,600,000,000		4,600,000,000		4,600,000,000

[1] Certain prior period amounts have been reclassified to conform with the current period presentation.

[2] Represents our dividend payments to Treasury under the terms of the senior preferred stock. Dividends distributed or available for distribution for the three months ended June 30, 2014 (relating to the dividend period for the three months ended September 30, 2014) were calculated based on our net worth as of June 30, 2014 less the applicable capital reserve amount of $2.4 billion and for the six months ended June 30, 2014 we add dividends paid on June 30, 2014 to this amount. Dividends distributed or available for distribution for the three months ended June 30, 2013 (relating to the dividend period for the three months ended September 30, 2013) were calculated based on our net worth as of June 30, 2013 less the applicable capital reserve amount of $3.0 billion and for the six months ended June 30, 2013 we add dividends paid on June 30, 2013 to this amount.

[3] Includes 4.6 billion of weighted average shares of common stock that would be issued upon the full exercise of the warrant issued to Treasury from the date the warrant was issued through June 30, 2014.