This is 100 manhattan projects. Lots and lots and lots of things that can be done. Reminds me of the quote "water water everywhere not a drop to drink" ==> Money, money everywhere, not a cent goes towards something remotely useful.
1) Could've added nifty features to roads (rf beacons?) and make it super easy to build autonomous vehicles. This would've solved so many problems, but most importantly 45,000 lives every year and millions of accidents.
2) Could've given the money to farmers who are getting ethanol subsidies today to add panels, supply tons of power to the grid, creating permanent income to the farmers instead of handouts every year.
3) Could've built many Universities permanently free which is feasible with an endowment that large.
4) Could've built walking/biking infrastructure in most cities, which would help reduce healthcare expenses. Most of the expenses today are lifestyle/metabolic diseases.
5) Could've switched the entire country to clean energy, exporting ALL of the oil and create a sovereign wealth fund.
6) Could've built a city for homeless people with homes, excess energy production (solar) providing the function of a UBI, a massive hospital with health and mental health facilities, de-addiction centers. New city in the middle of nowhere where land is dirt cheap. Army corps of engineers could execute this.
7) Rehabilitate prison (not like George Carlins suggestion of Kansas: https://www.youtube.com/watch?v=PkMrFIv_QHk), but more like nordic countries.
8) Build solar over all the interstates.