Regulatory Capital Requirements (Details) - USD ($) $ in Millions	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Regulatory Capital Requirements [Abstract]
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 critical capital requirement, percentage of the unpaid principal balance of outstanding Fannie Mae MBS held by third parties	0.45%
Net worth (deficit)	$ 6,240	$ 3,686	$ 6,071	$ 4,059
Core capital	(114,919)	(121,389)
Statutory minimum capital requirement	22,216	23,007
Deficit of core capital over statutory minimum capital requirement	$ (137,135)	(144,396)
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, 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 other off-balance sheet obligations	0.25%
Related Parties [Line Items]
Capital Reserve Amount, Fiscal Year, Senior Preferred Stock Purchase Agreement, Amendment		3,000
Stockholders' Equity, Including Portion Attributable to Noncontrolling Interest	$ 6,240	(3,686)
US Treasury [Member]
Related Parties [Line Items]
Aggregate funding received from US Treasury pursuant to the senior preferred stock purchase agreement	$ 119,800	$ 116,100	$ 116,100