Earnings Per Share (Details) - USD ($) $ / shares in Units, shares in Millions, $ in Millions	3 Months Ended
	Mar. 31, 2016	Mar. 31, 2015
Earnings Per Share [Abstract]
Net income attributable to Fannie Mae	$ 1,136	$ 1,888
Dividends distributed or available for distribution to senior preferred stockholder	(919)	(1,796)
Net income (loss) attributable to common stockholders	$ 217	$ 92
Weighted-average common shares outstanding, Basic	5,762	5,762
Convertible preferred stock	131	131
Weighted-average common shares outstanding, Diluted	5,893	5,893
Earnings (loss) per share, Basic (in dollars per share)	$ 0.04	$ 0.02
Earnings (loss) per share, Diluted (in dollars per share)	$ 0.04	$ 0.02
Weighted average shares of common stock that would be issued upon the full exercise of the warrant issued to Treasury	4,600	4,600