I can't even wrap my head around that much money. I don't think I'd even *want* that much money.
But here goes:
I'd start with the basics, like everyone has said. Family, friends, personal debt, etc.
I'd renovate my parents' house and move there, so they could live with us until they die. I'd get some more land so I could have a couple horses on site.
I'd create a retirement home for old/disabled/unwanted horses, that I would pair with a therapeutic center for disabled children.
I'd have to do a lot of research to find ONE other thing I could focus on to make a difference...
Just read that the six-year-old daughter of the Missouri couple who won wants a pony:
The couple have three grown sons and a 6-year-old daughter they adopted from China five years ago. They said they are now considering a second adoption with their winnings, and they plan to help other relatives, including their grandchildren and nieces and nephews, pay for college. They're planning vacations, and their daughter, Jaiden, wants a pony.