Berkshire Hathaway Chairman and CEO Warren BuffettBerkshire Hathaway Chairman and CEO Warren Buffett.

TheOracle of Omaha bought up Citi shares even though they have been lagging the rest of the financial sector. The Financial Select Sector SPDR Fund is off by 12% while the stock is down by 40%.

Jane Fraser was the first female chief of a major U.S. bank when she took over at Citi a year ago. She has set a medium-term target of 12% for return on tangible common equity, aiming to transform a company that has been badly underperformed by U.S. rivals for years.

13 retail markets in Asia and Europe have been left by Fraser.

Some of the rivals in the portfolio are now joined by Citi. At the end of March, Bank of America was owned by Warren Buffet's company. Bank of American has been owned by Warren Buffet's company.

A new stake in Ally Financial was built by the company. After the disclosure, the stock jumped 4% in premarket trading.

The conglomerate held shares in a number of companies. In the first quarter, the conglomerate exited its position in Wells Fargo.