Warren Buffett's stock portfolio from Berkshire Hathaway

The biggest change in Berkshire's portfolio is the sale of 10% of its stake in Chevron. We learned this from the disclosure in the third quarter earnings report. As of the end of September, the portfolio held company shares worth $18.6 billion.
Sale of 15% of its stake in Hewlett Packard. We learned this from the Form 4 disclosures that require Berkshire to disclose changes in ownership of companies in which it owns more than 10%. The company ended September with shares worth $2.6 billion, but continued to reduce its position in October.
Selling 100% of its position in Activision. Although investors knew that Berkshire no longer owned Activision following its acquisition by Microsoft, it appears that Buffett sold the remaining shares before the deal closed in October.
The 13F also revealed several positions in which Berkshire completely exited its positions in General Motors, Celanese, Johnson & Johnson, Procter & Gamble, Modelez and United Parcel Service. Some positions were reduced, including: 66% of Markel shares, resulting in the company received $233.7 million worth of stock at the end of the quarter.
67% of Globe Life, leaving him with shares worth $185.4 million at the end of the quarter.
5% stake in Amazon, leaving it with $1.3 billion worth of shares at the end of the quarter.
5% stake in Aon, leaving $1.3 billion worth of shares at the end of the quarter.
The portfolio also received a shake-up as a result of Liberty Media's spinoff of the Atlanta Braves and a reclassification of its track shares. It's worth noting that all of these newly revealed sales are relatively small. Berkshire hasn't made any major changes to its portfolio. In the end, the company sold a total of $7 billion worth of shares out of a $318 billion portfolio.

Purchase of 9.7 million shares of Sirius XM (SIRI).

Berkshire only reported one truly new 13F stock.

At the end of the quarter, the stake was worth about $44 million, representing about 0.01% (1/10,000) of the total portfolio value. So it wasn't that big of a purchase. The vast majority of Berkshire's $1.7 billion in stock purchases last quarter were for new, undisclosed mystery stocks. We can get some clues from Berkshire's third-quarter earnings report. The company reported that the cost basis of its investments in banking, insurance and financial equity securities increased by approximately $1.2 billion. Sales from Globe Life, Markel and Aon will also bring that figure down slightly, so it equates to $1.7 billion in purchases. One reason Berkshire might want to keep its new asset confidential is because it wants to continue buying shares of the company. Because changes in its portfolio are so widely watched, any disclosure could cause the stock price to rise significantly. Sirius XM shares rose as much as 15% the day after Berkshire filed its 13F. In other words, if you can figure out what Buffett and his team bought last quarter, you might be able to invest before the Oracle of Omaha.