v3.26.1
Short-Term and Long-Term Debt - Long-Term Debt (Details) - USD ($)
$ in Millions
 3 Months Ended 12 Months Ended
Mar. 31, 2026
Dec. 31, 2025
Long-Term Debt [Line Items]    
Long-term debt, outstanding $ 4,152,200 $ 4,155,891
Long-term debt, weighted-average interest rate (percent) 3.17% 3.16%
Fannie Mae    
Long-Term Debt [Line Items]    
Long-term debt, outstanding $ 129,836 $ 102,751
Long-term debt, weighted-average interest rate (percent) 3.78% 3.89%
Unamortized discounts and premiums, fair value adjustments, hedge-related cost basis adjustments, and other cost basis adjustments $ 2,500 $ 2,600
Fannie Mae | Total senior fixed    
Long-Term Debt [Line Items]    
Long-term debt, outstanding $ 77,166 $ 64,688
Long-term debt, weighted-average interest rate (percent) 3.68% 3.70%
Fannie Mae | Senior fixed benchmark notes and bonds    
Long-Term Debt [Line Items]    
Long-term debt, outstanding $ 26,704 $ 26,649
Long-term debt, weighted-average interest rate (percent) 4.15% 4.16%
Fannie Mae | Senior fixed medium-term notes    
Long-Term Debt [Line Items]    
Long-term debt, outstanding $ 43,859 $ 31,430
Long-term debt, weighted-average interest rate (percent) 3.34% 3.25%
Fannie Mae | Senior fixed medium-term notes | Minimum    
Long-Term Debt [Line Items]    
Contractual maturity term 1 year 1 year
Fannie Mae | Senior fixed medium-term notes | Maximum    
Long-Term Debt [Line Items]    
Contractual maturity term 10 years 10 years
Fannie Mae | Senior fixed other debt    
Long-Term Debt [Line Items]    
Long-term debt, outstanding $ 6,603 $ 6,609
Long-term debt, weighted-average interest rate (percent) 3.85% 3.87%
Contractual maturity term 10 years 10 years
Fannie Mae | Total senior floating    
Long-Term Debt [Line Items]    
Long-term debt, outstanding $ 52,670 $ 38,063
Long-term debt, weighted-average interest rate (percent) 3.94% 4.23%
Fannie Mae | Senior floating medium-term notes    
Long-Term Debt [Line Items]    
Long-term debt, outstanding $ 51,436 $ 36,437
Long-term debt, weighted-average interest rate (percent) 3.78% 3.93%
Fannie Mae | Senior floating other debt    
Long-Term Debt [Line Items]    
Long-term debt, outstanding $ 1,234 $ 1,626
Long-term debt, weighted-average interest rate (percent) 10.48% 10.99%
Consolidated Trusts    
Long-Term Debt [Line Items]    
Long-term debt, outstanding $ 4,022,364 $ 4,053,140
Long-term debt, weighted-average interest rate (percent) 3.15% 3.14%