Financial Guarantees (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020
Financial Guarantees and Maximum Recovery [Line Items]
Contractual terms of our guarantees	31 years
Maximum exposure	$ 14,156	$ 16,252
Guaranty obligation	101	127
Maximum recovery	5,743	6,664
Unconsolidated Fannie Mae MBS | Unconsolidated VIEs
Financial Guarantees and Maximum Recovery [Line Items]
Maximum exposure	3,733	4,424
Guaranty obligation	16	18
Maximum recovery	3,626	4,226
Other guaranty arrangements | Unconsolidated VIEs
Financial Guarantees and Maximum Recovery [Line Items]
Maximum exposure	10,423	11,828
Guaranty obligation	85	109
Maximum recovery	2,117	2,438
Other agency | Unconsolidated VIEs
Financial Guarantees and Maximum Recovery [Line Items]
Freddie Mac collateral included in Fannie Mae commingled security	$ 212,300	$ 137,300