Income Taxes - Narratives (Details) (USD $)	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		Dec. 31, 2010
Income Tax Contingency [Line Items]
Valuation allowance	$ 525,000,000					$ 525,000,000		$ 58,851,000,000
Cumulative income loss position (years)					3 years
Capital Loss Carryforward, Valuation Allowance	(525,000,000)					(525,000,000)
(Provision) benefit for federal income taxes	(1,816,000,000)		(1,355,000,000)	(1,985,000,000)	50,571,000,000	45,415,000,000	[1]	0		90,000,000
Deferred tax assets (liabilities), net	47,560,000,000					47,560,000,000		(509,000,000)
Deferred Tax Assets, Operating Loss Carryforwards	0					0
Capital loss carryforwards	1,600,000,000					1,600,000,000
Deferred Tax Assets, Tax Credit Carryforwards, Partnership, Net of Uncertain Tax Position Liabilities	4,400,000,000					4,400,000,000
Deferred Tax Assets, Tax Credit Carryforwards, Alternative Minimum Tax	330,000,000					330,000,000
Unrecognized Tax Benefits	514,000,000	[2]				514,000,000	[2]	648,000,000	[2]	758,000,000	[2]	864,000,000
Unrecognized tax benefits that was resolved favorably and reduced our effective tax rate	0					0		0				60,000,000
Accrued interest payable related to unrecognized tax benefits	0					0		0
Interest expense related to unrecognized tax benefits						0		0
Settlements						0		0		(105,000,000)
Statutory corporate tax rate						35.00%		35.00%		35.00%
Deferred income tax benefit						48,482,000,000	[3]	0	[3]	0	[3]
Proceeds from income tax refunds										1,100,000,000
Change in income tax provision due to valuation allowance changes						58,300,000,000		5,300,000,000		(7,000,000,000)
Forecast for unrecognized tax benefits, next 12 months [Member]
Income Tax Contingency [Line Items]
Settlements						$ (514,000,000)

[1] 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.

[2] Amounts exclude tax credits of $220 million as of December 31, 2013 and exclude tax credits and net operating losses of $648 million and $758 million as of December 31, 2012 and 2011, respectively.

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