v3.26.1
Short-Term and Long-Term Debt - Short-Term Debt (Details) - Fannie Mae - USD ($)
$ in Millions
Mar. 31, 2026
Dec. 31, 2025
Short-Term Debt [Line Items]    
Short-term debt, outstanding $ 20,602 $ 24,538
Short-term debt, weighted-average interest rate (percent) 3.40% 3.66%