Earnings Per Share (Details) - USD ($) $ / shares in Units, shares in Millions, $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2016	Jun. 30, 2015	Jun. 30, 2016	Jun. 30, 2015
Earnings Per Share [Abstract]
Net income attributable to Fannie Mae	$ 2,946	$ 4,640	$ 4,082	$ 6,528
Dividends distributed or available for distribution to senior preferred stockholder	(2,869)	(4,359)	(3,788)	(6,155)
Net income attributable to common stockholders	$ 77	$ 281	$ 294	$ 373
Weighted-average common shares outstanding, Basic	5,762	5,762	5,762	5,762
Convertible preferred stock	131	131	131	131
Weighted-average common shares outstanding, Diluted	5,893	5,893	5,893	5,893
Earnings (loss) per share, Basic (in dollars per share)	$ 0.01	$ 0.05	$ 0.05	$ 0.06
Earnings (loss) per share, Diluted (in dollars per share)	$ 0.01	$ 0.05	$ 0.05	$ 0.06
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