Earnings Per Share (Details) (USD $)	0 Months Ended	3 Months Ended
	Mar. 29, 2013	Mar. 31, 2013		Mar. 31, 2012
Earnings Per Share [Abstract]
Net income (loss)		$ 58,685,000,000		$ 2,718,000,000
Less: Net loss attributable to noncontrolling interest		0		1,000,000
Net income (loss) attributable to Fannie Mae		58,685,000,000		2,719,000,000
Dividends distributed to senior preferred stockholder				(2,817,000,000)	[1]
Dividends available for distribution to senior preferred stockholder		(59,368,000,000)	[1]	0
Net income (loss) attributable to common stockholders		(683,000,000)		(98,000,000)
Weighted-average common shares outstanding, Basic		5,762,000,000	[2]	5,761,000,000	[2]
Weighted-average common shares outstanding, Diluted		5,762,000,000	[2]	5,761,000,000	[2]
Earnings (loss) per share, Basic		$ (0.12)		$ (0.02)
Earnings (loss) per share, Diluted		$ (0.12)		$ (0.02)
Capital reserve amount for 2013 per the senior preferred stock purchase agreement amendment		3,000,000,000
Senior preferred stock dividend rate in effect through December 31, 2012				10.00%
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
Payments of cash dividends on senior preferred stock to Treasury	4,224,000,000	4,224,000,000		2,819,000,000
Dividends payable on senior preferred stock for the next quarter		$ 59,368,000,000
Antidilutive weighted-average stock options excluded from computation of diluted EPS		1,000,000		3,000,000

[1] Represents our required dividend payments to Treasury under the terms of the senior preferred stock purchase agreement, which are calculated based on our net worth as of March 31, 2013 less the applicable capital reserve amount of $3.0 billion for the three months ended March 31, 2013 and an annual dividend rate of 10% on the aggregate liquidation preference for the three months ended March 31, 2012.

[2] Includes 4.6 billion for the three months ended March 31, 2013 and 2012 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 March 31, 2013.