"Put 10% of the cash in short-term government bonds and 90% in a very low-cost S&P 500 index fund," Buffett wrote in 2013.

Investors often use Berkshire Hathaway's quarterly-filed Form 13Fs to track Warren Buffett's trading activity. Buffett has been a net seller of stocks for nine consecutive quarters, which has ballooned Berkshire's cash pile to $334 billion.