Another move appears to be the work of a portfolio manager. Berkshire added 2,948,285 shares of Liberty Global, John Malone's London-based international cable company. That stake was worth about $245 million as of Friday's close.
There were no other major additions to the portfolio, other than previously disclosed new or additional shares of Goldman Sachs, General Electric, USG and DaVita Healthcare Partners.
(Read more: Berkshire Hathaway's 15 biggest stock holdings)
Last October, Berkshire coverted Goldman warrants into more than $2 billion of common stock. The warrants were part of a 2008 loan deal.
Under similar deals, Berkshire received almost 11 million GE shares in mid-October and more than 21 million shares of USG in December.
The DaVita share purchases were most recently disclosed in early December.
Berkshire cut its holdings of ConocoPhillips by 18.1 percent during the fourth quarter, moving to 11.08 million shares from 13.53 million shares, a reduction of $160 million at the current price.
It cut its stake in Suncor Energy by 27.8 percent, to 13 million shares from 18 million—a $167 million reduction.