Key Takeaways Warren Buffett's Berkshire Hathaway revealed in a regulatory filing that the 'mystery stock' the conglomerate has been buying is insurer Chubb. The quarterly 13F also confirmed that Berkshire sold around around 116 million shares of Apple in the first quarter, while also jettisoning most of its stake in Paramount Global. Berkshire sold all of the nearly 23 million shares it owned in HP Inc., while adding slightly to its stake in Occidental Petroleum and significantly boosting its holdings in L ...