I have seen estimates of up to $1 trillion, but I haven't seen their analysis to reach that number.
Fannie Mae and Freddie Mac were taken into conservatorship by the FHFA in September 2008. Since the end of 2007, the GSEs have lost $226 billion with 73% of that stemming from the single-family credit guarantee business. The Treasury has recorded losses of $148 billion attributable to its bailout of Fannie and Freddie.
Also, I guess this figure...is just a guess
DeMarco said the FHFA is working with the GSEs to develop financial projections, but the results will be modeled projections not forecasts or expected outcomes, according to DeMarco.