Seriously, I have no idea what I'd do with that amount of money. If I was completely selfish maybe I'd buy an island somewhere. I sure as hell wouldn't use it to bail out a bunch of failed businesses whose executives have been giving themselves multi-million dollar bonuses.
I would invest it. I would buy most of wall street and wait for it to bounce back. Turn that 700b to 10 trillion.
I think it would actually be pretty hard to find ways to spend that much money. 10 trillion is an awful lot.
I don't claim to have the answers.. but I think it will take a lot more than money to solve these problems. That's assuming they can even be solved at all.
Seriously, since the moon base was pretty selfish, I should give a serious answer. I think a series of X-Prize ideas, in the $10-20 Billion range, would transform our society in ways we can barely imagine. Fusion, solar power, field propulsion -- it would be like having a war and pushing for new technology without going through all the death and destruction.