Warren Buffett had a couple of billion-dollar loser days in October, and so far January isn't doing him any favors either.
IBM's 3.6 percent drop in early trading Wednesday cost the "Oracle of Omaha" some $397 million, based on his 70,478,012 shares as of September 30. (His end-of-year holdings won't be public until mid-February).
Since Buffett first disclosed his IBM stake in November 2011, the stock is down about 10 percent.
That said, he has reiterated his support for the company over the years and stood by his investment, one of the largest on his books.