Short-Term and Long-Term Debt - Characteristics of Debt (Details) - USD ($) $ in Millions	Dec. 31, 2023	Dec. 31, 2022
Long-Term Debt by Year of Maturity [Abstract]
Total long-term debt	$ 4,205,404	$ 4,211,684
Assuming Callable Debt Redeemed at Next Available Call Date
Long-Term Debt by Year of Maturity [Abstract]
Total long-term debt	4,205,404
Fannie Mae
Long-Term Debt [Line Items]
Face amount	128,100	139,300
Long-Term Debt by Year of Maturity [Abstract]
2024	23,354
2025	39,026
2026	10,289
2027	5,974
2028	3,681
Thereafter	24,427
Total long-term debt	106,751	123,964
Fannie Mae | Zero-coupon debt
Long-Term Debt [Line Items]
Face amount	$ 11,600	$ 10,000
Effective interest rate	5.06%	3.91%
Fannie Mae | Callable
Long-Term Debt [Line Items]
Outstanding debt	$ 43,800	$ 43,300
Fannie Mae | Assuming Callable Debt Redeemed at Next Available Call Date
Long-Term Debt by Year of Maturity [Abstract]
2024	54,192
2025	21,153
2026	6,983
2027	4,170
2028	1,462
Thereafter	18,791
Total long-term debt	106,751
Consolidated Trusts
Long-Term Debt by Year of Maturity [Abstract]
Total long-term debt	4,098,653	$ 4,087,720
Consolidated Trusts | Assuming Callable Debt Redeemed at Next Available Call Date
Long-Term Debt by Year of Maturity [Abstract]
Total long-term debt	$ 4,098,653