Warren Buffett resigned Wednesday as trustee of the Bill and Melinda Gates Foundation, which says it will announce plans in July to answer questions raised about its leadership structure. The announcement from Buffett comes weeks after Bill and Melinda Gates announced that they were divorcing after 27 years of marriage but would continue to jointly run the foundation. It's one of the largest charitable foundations in the world. Buffett also said Wednesday that he is halfway to reaching his goal of giving away the entirety of his shares in Berkshire Hathaway, his company. He says he's donating another $4.1 billion in shares to five foundations.