Guarantees (Policies)	3 Months Ended
	Mar. 31, 2020
Guarantees and Product Warranties [Abstract]
Off-Balance-Sheet Credit Exposure, Policy	We recognize a guaranty obligation for our obligation to stand ready to perform on our guarantees to unconsolidated trusts and other guaranty arrangements. These off-balance sheet guarantees expose us to credit losses primarily relating to the unpaid principal balance of our unconsolidated Fannie Mae MBS and other financial guarantees.With our adoption of the CECL standard on January 1, 2020, we measure our guaranty reserve for estimated credit losses for off-balance sheet exposures over the contractual period for which they are exposed to the credit risk, unless that obligation is unconditionally cancellable by the issuer.