v3.26.1
Short-Term and Long-Term Debt - Long-Term Debt (Details) - USD ($)
$ in Millions
 6 Months Ended 12 Months Ended
Jun. 30, 2026
Dec. 31, 2025
Long-Term Debt [Line Items]    
Long-term debt, outstanding $ 4,160,591 $ 4,155,891
Long-term debt, weighted-average interest rate (percent) 3.20% 3.16%
Fannie Mae    
Long-Term Debt [Line Items]    
Long-term debt, outstanding $ 147,768 $ 102,751
Long-term debt, weighted-average interest rate (percent) 3.93% 3.89%
Unamortized discounts and premiums, fair value adjustments, hedge-related cost basis adjustments, and other cost basis adjustments $ 2,600 $ 2,600
Fannie Mae | Total senior fixed    
Long-Term Debt [Line Items]    
Long-term debt, outstanding $ 83,228 $ 64,688
Long-term debt, weighted-average interest rate (percent) 3.98% 3.70%
Fannie Mae | Senior fixed benchmark notes and bonds    
Long-Term Debt [Line Items]    
Long-term debt, outstanding $ 23,165 $ 26,649
Long-term debt, weighted-average interest rate (percent) 4.61% 4.16%
Fannie Mae | Senior fixed medium-term notes    
Long-Term Debt [Line Items]    
Long-term debt, outstanding $ 53,650 $ 31,430
Long-term debt, weighted-average interest rate (percent) 3.69% 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 $ 6,413 $ 6,609
Long-term debt, weighted-average interest rate (percent) 3.94% 3.87%
Contractual maturity term 10 years 10 years
Fannie Mae | Total senior floating    
Long-Term Debt [Line Items]    
Long-term debt, outstanding $ 64,540 $ 38,063
Long-term debt, weighted-average interest rate (percent) 3.87% 4.23%
Fannie Mae | Senior floating medium-term notes    
Long-Term Debt [Line Items]    
Long-term debt, outstanding $ 63,434 $ 36,437
Long-term debt, weighted-average interest rate (percent) 3.75% 3.93%
Fannie Mae | Senior floating other debt    
Long-Term Debt [Line Items]    
Long-term debt, outstanding $ 1,106 $ 1,626
Long-term debt, weighted-average interest rate (percent) 10.63% 10.99%
Consolidated Trusts    
Long-Term Debt [Line Items]    
Long-term debt, outstanding $ 4,012,823 $ 4,053,140
Long-term debt, weighted-average interest rate (percent) 3.18% 3.14%