He was blindsided by huge derivatives when Birkshire Hathaway

purchased the General Re. He fired all the traders there and spent lots of money (including huge losses) and time to unwind those derivatives.  

On the other hand, through private deals(I believe a Goldman Sachs broker pitched in), he sold many long term naked puts(on year 2018 and beyond) on Europe market indexes (as well as S&P 500 indexes) and pocketed billions of premium. They are pretty much like his deals with BAC, GE and GS during financial crisis in 2008.  Well, as he mentioned in shareholder meeting last weekend, those deals are just pocket changes for Birkshire Hathaway. At the same meeting, he also promised when his successor takes over the company, all derivatives will be cleared up.