Berkshire Hathaway, Buffett’s investment group, disclosed it had bought 5 million shares of the healthcare company earlier in the year. That sparked a 14% Friday rally in a stock that has lost more than half of its value over the past 12 months.

Berkshire Hathaway’s $1 billion homebuilding investment indicates Warren Buffett’s confidence in a future U.S. housing market rebound.

Quarterly filed Form 13Fs provide a way for investors to track the buying and selling activity of Wall Street's top money managers. Warren Buffett is occasionally granted the "confidential treatment" tag,