The "Fedwire Funds Service" is the Federal Reserve's wire transfer payment system used to move USD. I'm actually writing an integration to it right this moment (the old fixed-width format, not the new XML one, yay). Naturally this interface is not available directly to retail customers, but if you actually send a wire transfer from your bank, this is the system you will use.

Your bank will generally make this available to you through some online interface. If not, you can visit the teller. They will likely charge you $20-$40 to send a wire if you are a small account, but, even with something like Chase's mid-level "Signature" checking (~$10-$20k minimum to avoid monthly fees iirc) they will waive this fee. And, of course, if you're really moving a billion, not only would you have a banking relationship where your wire fees are waived, that fee would be peanuts anyway.