OP, if this is anything more than “hypothetically”, you are absolutely definitely being scammed right now. Break off chat with the “billionaire”. If you’ve given them your financial details, call the phone number printed on the back of your bank card. If you use Windows or MacOS, run a scan with Seraph Secure to make sure nobody has remote access to your computer.

That said: billionaires deal with banks and financial institutions of all kinds all the time. They’ll have their bank communicate directly with your bank before making a bank transfer, so both banks know exactly what’s happening. You may need to pay tax on the donation/investment. Use some of the money to hire an accountant.