Regulatory Capital Requirements (Details) - USD ($)	Dec. 31, 2020	Sep. 30, 2020	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Broker-Dealer, Net Capital Requirement, SEC Regulation [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)	$ 25,259,000,000		$ 14,608,000,000	$ 6,240,000,000	$ (3,686,000,000)
Core capital	(95,694,000,000)		(106,360,000,000)
Statutory minimum capital requirement	28,603,000,000		22,392,000,000
Deficit of core capital over statutory minimum capital requirement	$ (124,297,000,000)		(128,752,000,000)
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]
Stockholders' Equity, Including Portion Attributable to Noncontrolling Interest	$ 25,259,000,000		14,608,000,000
US Treasury [Member]
Related Parties [Line Items]
Aggregate funding received from US Treasury pursuant to the senior preferred stock purchase agreement	$ 119,800,000,000
Capital Reserve Amount, Fiscal Year, Senior Preferred Stock Purchase Agreement, Amendment		$ 25,000,000,000	$ 3,000,000,000		$ 3,000,000,000