Financial Guarantees and Maximum Recovery (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019
Financial Guarantees and Maximum Recovery [Line Items]
Contractual terms of our guarantees	32 years
Maximum exposure	$ 16,252	$ 18,471
Guaranty obligation	127	154
Maximum recovery	6,664	8,098
Unconsolidated Fannie Mae MBS [Member] | Unconsolidated VIEs [Member]
Financial Guarantees and Maximum Recovery [Line Items]
Maximum exposure	4,424	5,801
Guaranty obligation	18	26
Maximum recovery	4,226	5,545
Other guaranty arrangements [Member] | Unconsolidated VIEs [Member]
Financial Guarantees and Maximum Recovery [Line Items]
Maximum exposure	11,828	12,670
Guaranty obligation	109	128
Maximum recovery	2,438	2,553
Mortgage-backed Securities, Issued by US Government Sponsored Enterprises [Member] | Unconsolidated VIEs [Member]
Financial Guarantees and Maximum Recovery [Line Items]
Freddie Mac collateral included in Fannie Mae commingled security	$ 137,300	$ 50,100