Much of that money isn't kept out of the U.S. economy indefinitely, not even for the time being. It is loaned to others such that they can spend it. That is the nature of savings, at least on such a scale.
Much of that money is loaned to other corporations and thusly used for various purposes - e.g., to build things to grow those businesses, to pay employees, to return money to shareholders (who pay additional taxes on it and themselves use it in various ways). A lot of it is loaned to the U.S. government, much smaller amounts are loaned to foreign governments. Some of it is loaned to homeowners helping more people to buy homes.
That's to say nothing of the massive amounts of money that Apple spends or invests or returns to shareholders itself, or that it pays in U.S. taxes.
When we say that money is held overseas or offshore, we don't really mean that it isn't in U.S.-based assets. It could be in a U.S. bank or loaned to a U.S. company or the U.S. government. What we typically mean is that it hasn't been distributed to a parent (domestic) company from a subsidiary (foreign) company which made it and which that parent company owns. It's similar (though also different in a number of ways) to profits that a corporation makes not having been distributed yet to shareholders. The foreign company can still do lots of things with that money, including things which effectively channel it into the U.S. economy.
