Income Taxes - Benefit for Income Taxes (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended				12 Months Ended
	Dec. 31, 2013	Sep. 30, 2013	Jun. 30, 2013	Mar. 31, 2013	Dec. 31, 2013		Dec. 31, 2012		Dec. 31, 2011
Income Tax Expense (Benefit), Continuing Operations, Income Tax Reconciliation [Abstract]
Current income tax benefit					$ (3,067)		$ 0		$ 90
Deferred income tax benefit					48,482	[1]	0	[1]	0	[1]
(Provision) benefit for federal income taxes	$ (1,816)	$ (1,355)	$ (1,985)	$ 50,571	$ 45,415	[2]	$ 0		$ 90
Effective Income Tax Rate, Continuing Operations, Tax Rate Reconciliation [Abstract]
Statutory corporate tax rate					35.00%		35.00%		35.00%
Tax-exempt interest					(0.20%)		(0.70%)		0.90%
Equity investments in affordable housing projects					(1.50%)		(3.90%)		4.80%
Other					0.20%		0.20%		1.00%
Valuation allowance					(151.30%)		(30.60%)		(41.20%)
Effective tax rate					(117.80%)		0.00%		0.50%

[1] Amount excludes the income tax effect of items recognized directly in “Fannie Mae stockholders’ equity (deficit).”

[2] Primarily represents the release of the valuation allowance for our deferred tax assets that generally are directly attributable to each segment based on the nature of the item.