Lack of cash is not one of Apple's problems. If they wanted to invest more in the US they could.

Most of the money will probably just sit still in a wide variety of investments (bonds and other stuff; Apple is one of the biggest players in these markets); the rest will go into dividends and share buybacks. A symbolic percentage might go into R&D and Trump will tweet about it.

(I might be wrong, but that is what I expect.)