Short-Term and Long-Term Debt - Long-Term Debt (Details) - USD ($) $ in Millions	Dec. 31, 2022	Dec. 31, 2021
Long-Term Debt [Line Items]
Long-term debt, outstanding	$ 4,211,684	$ 4,155,396
Long-term debt, weighted-average interest rate	2.47%	1.88%
Fannie Mae
Long-Term Debt [Line Items]
Long-term debt, outstanding	$ 123,964	$ 198,097
Long-term debt, weighted-average interest rate	2.23%	1.55%
Net unamortized discount, fair value adjustments and other cost basis adjustments	$ 5,100	$ 1,600
Fannie Mae | Senior Fixed
Long-Term Debt [Line Items]
Long-term debt, outstanding	$ 118,515	$ 134,975
Long-term debt, weighted-average interest rate	1.94%	1.78%
Fannie Mae | Benchmark notes and bonds
Long-Term Debt [Line Items]
Long-term debt, outstanding	$ 72,261	$ 89,618
Long-term debt, weighted-average interest rate	2.35%	2.13%
Fannie Mae | Medium-term notes
Long-Term Debt [Line Items]
Long-term debt, outstanding	$ 39,476	$ 38,312
Long-term debt, weighted-average interest rate	0.78%	0.60%
Fannie Mae | Other
Long-Term Debt [Line Items]
Long-term debt, outstanding	$ 6,778	$ 7,045
Long-term debt, weighted-average interest rate	4.00%	3.73%
Fannie Mae | Senior floating
Long-Term Debt [Line Items]
Long-term debt, outstanding	$ 5,449	$ 63,122
Long-term debt, weighted-average interest rate	8.86%	1.05%
Fannie Mae | Medium-term notes
Long-Term Debt [Line Items]
Long-term debt, outstanding	$ 0	$ 51,583
Long-term debt, weighted-average interest rate	0.00%	0.32%
Fannie Mae | Connecticut Avenue Securities
Long-Term Debt [Line Items]
Long-term debt, outstanding	$ 5,207	$ 11,166
Long-term debt, weighted-average interest rate	8.80%	4.30%
Fannie Mae | Other
Long-Term Debt [Line Items]
Long-term debt, outstanding	$ 242	$ 373
Long-term debt, weighted-average interest rate	10.00%	7.17%
Consolidated Trusts
Long-Term Debt [Line Items]
Long-term debt, outstanding	$ 4,087,720	$ 3,957,299
Long-term debt, weighted-average interest rate	2.47%	1.89%