Short-Term and Long-Term Debt Characteristics of Debt (Details) - USD ($) $ in Millions	Dec. 31, 2019	Dec. 31, 2018
Long-Term Debt by Year of Maturity [Abstract]
Total long-term debt	$ 3,440,724	$ 3,367,024
Consolidated Trusts [Member]
Long-Term Debt by Year of Maturity [Abstract]
Total long-term debt	3,285,139	3,159,846
Earlier of Contractual Maturity or Next Call Date [Member]
Long-Term Debt by Year of Maturity [Abstract]
Total long-term debt	3,440,724
Earlier of Contractual Maturity or Next Call Date [Member] \| Consolidated Trusts [Member]
Long-Term Debt by Year of Maturity [Abstract]
Total long-term debt	3,285,139
Fannie Mae [Member]
Long-Term Debt [Line Items]
Face amount	182,200	232,500
Long-Term Debt by Year of Maturity [Abstract]
2020	47,427
2021	29,028
2022	15,584
2023	5,301
2024	14,344
Thereafter	43,901
Total long-term debt	155,585	207,178
Net unamortized discount, fair value adjustments and other cost basis adjustments	2	413
Fannie Mae [Member] \| Zero-Coupon Debt [Member]
Long-Term Debt [Line Items]
Face amount	$ 23,100	$ 23,200
Effective interest rate	1.63%	4.15%
Fannie Mae [Member] \| Callable [Member]
Long-Term Debt [Line Items]
Outstanding debt	$ 38,500	$ 64,300
Fannie Mae [Member] \| Earlier of Contractual Maturity or Next Call Date [Member]
Long-Term Debt by Year of Maturity [Abstract]
2020	60,464
2021	21,037
2022	14,010
2023	4,470
2024	13,320
Thereafter	42,284
Total long-term debt	$ 155,585

Amount, before unamortized (discount) premium and debt issuance costs, of long-term debt. Includes, but is not limited to, notes payable, bonds payable, commercial loans, mortgage loans, convertible debt, subordinated debt and other types of debt.

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