Commitments and Contingencies (Details) (USD $)	12 Months Ended				0 Months Ended				12 Months Ended				1 Months Ended		12 Months Ended		1 Months Ended		12 Months Ended
	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2008 Pending Litigation [Member] 2008 Class Action Lawsuits [Member] cases	Oct. 22, 2012 Pending Litigation [Member] In re 2008 Fannie Mae ERISA Litigation [Member] defendants	Mar. 02, 2012 Pending Litigation [Member] In re 2008 Fannie Mae ERISA Litigation [Member] defendants	Aug. 30, 2012 Pending Litigation [Member] Comprehensive Investment Services v. Mudd, et al. [Member] defendants	Jul. 30, 2008 Pending Litigation [Member] Housing Trust Fund [Member]	Dec. 31, 2010 Unasserted Claim [Member] Minimum [Member] Pending Litigation [Member] In re Fannie Mae Securities Litigation [Member]	Dec. 31, 2010 Unasserted Claim [Member] Maximum [Member] Pending Litigation [Member] In re Fannie Mae Securities Litigation [Member]	Dec. 31, 2013 Series T Preferred Stock [Member]		May 31, 2008 Series T Preferred Stock [Member] Pending Litigation [Member] Comprehensive Investment Services v. Mudd, et al. [Member]	May 19, 2008 Series T Preferred Stock [Member] Pending Litigation [Member] Comprehensive Investment Services v. Mudd, et al. [Member]	Dec. 31, 2013 Series S Preferred Stock [Member]		Dec. 31, 2007 Series S Preferred Stock [Member] Pending Litigation [Member] Smith v. Fannie Mae, et al. [Member]	Dec. 11, 2007 Series S Preferred Stock [Member] Pending Litigation [Member] Smith v. Fannie Mae, et al. [Member]	Dec. 31, 2013 Series S Preferred Stock [Member] Minimum [Member]
Loss Contingencies [Line Items]
Damages claimed to plaintiffs under various scenarios									$ 2,200,000,000	$ 8,600,000,000
Number of lawsuits that Fannie Mae is a defendant				2
Number of current Board members added as defendants						2
Number of former and current directors and officers dismissed from the action					7		2
Preferred stock offering amount														2,000,000,000				7,000,000,000
Preferred stock, annual dividend rate											8.25%	[1]	8.25%		7.75%	[2]	7.75%		7.75%
Basis Points of Each Dollar of Unpaid Principal Balance								0.042%
Percentage of the funds set aside as required by the Federal Housing Finance Regulatory Reform Act of 2008 that should be allocated to the Housing Trust Fund								65.00%
Percentage of the funds set aside as required by the Federal Housing Finance Regulatory Reform Act of 2008 that should be allocated to the Capital Magnet Fund								35.00%
Rent expenses for operating leases	$ 41,000,000	$ 41,000,000	$ 40,000,000

[1] On May 19, 2008, we issued 80 million shares of preferred stock in the amount of $2.0 billion. Subsequent to the initial issuance, we issued an additional 8 million shares in the amount of $200 million on May 22, 2008 and one million shares in the amount of $25 million on June 4, 2008 under the same terms as the initial issuance.

[2] Rate effective December 31, 2013. Variable dividend rate resets quarterly thereafter at a per annum rate equal to the greater of 7.75% or 3-Month LIBOR plus 4.23%.