Billionaire Warren Buffett's company is expected to file an update on its U.S. stock portfolio Wednesday after the markets close.

Berkshire Hathaway's investments are watched closely because many investors try to copy Buffett's moves.

The quarterly report will show Berkshire's holdings as of Sept. 30, so some of the information could be out of date.

Also, the report doesn't distinguish between Buffett's stock picks and those made by the company's other investment managers, Todd Combs and Ted Weschler. Combs started at Berkshire last year, and Weschler started early this year.

Combs and Weschler are both managing roughly $4 billion for Berkshire.

Buffett has said that investments smaller than $300 million are likely to be the work of Combs or Weschler.