Earnings (Loss) Per Share (Details) - USD ($) $ / shares in Units, shares in Millions, $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2016	Sep. 30, 2015	Sep. 30, 2016	Sep. 30, 2015
Earnings Per Share [Abstract]
Net income attributable to Fannie Mae	$ 3,196	$ 1,960	$ 7,278	$ 8,488
Dividends distributed or available for distribution to senior preferred stockholder	(2,977)	(2,202)	(6,765)	(8,357)
Net income attributable to common stockholders	$ 219	$ (242)	$ 513	$ 131
Weighted-average common shares outstanding, Basic	5,762	5,762	5,762	5,762
Convertible preferred stock	131	0	131	131
Weighted-average common shares outstanding, Diluted	5,893	5,762	5,893	5,893
Earnings (loss) per share, Basic (in dollars per share)	$ 0.04	$ (0.04)	$ 0.09	$ 0.02
Earnings (loss) per share, Diluted (in dollars per share)	$ 0.04	$ (0.04)	$ 0.09	$ 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	4,600	4,600