Alphaville presents a Moddy's review of US corporate cash piles – an amazingly high proportion is held by Apple:

"Apple alone represents $64 billion or 36% of the total $179 billion increase in corporate cash since 2009. And in 2011, overall corporate cash would have actually declined by $6 billion had it not been for Apple’s $46 billion increase. …

"Apple alone could represent 12% of total corporate cash, about three times more than the next cash king. …"

As Alphaville notes, America's top five companies account for 22% of the total.