Shares of UnitedHealth Group are surging before the market open Friday as Warren Buffett's Berkshire Hathaway disclosed that it recently purchased shares of the beleaguered insurer.

Berkshire Hathaway bought around 5 million shares of UnitedHealth last quarter, according to a regulatory filing. The stake was valued at about $1.57 billion.

Buffett plans to retire as CEO at the end of the year after six decades of building Berkshire Hathaway. Many investors comb through Berkshire’s filings every quarter because they like to follow Buffett’s moves.

The filing doesn’t make clear who at Berkshire handled the investment. Besides Buffett, Ted Weschler and Todd Combs also pick stocks, but they generally handle smaller portfolios and Combs also serves as Geico’s CEO.

Besides stocks, Berkshir

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