Regulatory Capital Requirements (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Regulatory Capital Requirements [Abstract]
Number of days of that liabilities exceed assets requiring FHFA to place us into receivership	60 days
Net worth (deficit)	$ 3,720	$ 9,591	$ 7,224	$ (4,571)
Core Capital	(115,202)	(108,811)
Statutory minimum capital requirement	27,044	28,472
Deficit Of Core Capital Over Statutory Minimum Capital Requirement	$ (142,246)	$ (137,283)
Component of statutory minimum capital requirement, percentage of on-balance sheet assets, except those underlying Fannie Mae MBS held by third parties	2.50%
Component of statutory minimum capital requirement, percentage of the unpaid principal balance of outstanding Fannie Mae MBS held by third parties	0.45%
Component of statutory minimum capital requirement, maximum percentage of other off-balance sheet obligations	0.45%
Component of critical capital requirement, percentage of on-balance sheet assets, except those underlying Fannie Mae MBS held by third parties	1.25%
Component of critical capital requirement, percentage of the unpaid principal balance of outstanding Fannie Mae MBS held by third parties	0.25%
Component of critical capital requirement, percentage of other off-balance sheet obligations	0.25%