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Warren Buffett added about $6 billion to Berkshire Hathaway’s considerable cash reserves this summer with a series of Bank of America share sales since mid-July.

According to a new document filed Friday, sales of 21.1 million shares on Wednesday, Thursday and Friday generated $848.2 million, for an average price of $40.24.

Berkshire has sold Bank of America shares for six straight sessions. Since it began reducing its stake on July 17, it has sold shares in 21 of the last 33 sessions.

In total, Berkshire has reduced its BofA stock by 14.5%, selling 150.1 million shares for $6.2 billion, an average of $41.33 per share.

BofA is the third largest equity holding in Berkshire, representing approximately 11% of the portfolio.

Berkshire remains Bank of America’s largest shareholder with an 11.4% stake of 882.7 million shares, worth nearly $36 billion.

As the sale continues, the number of Vanguard Group shares is approaching 639 million.

While there are several theories about why Berkshire is selling stocks that Buffett said last year he didn’t want to sell despite his concerns about the banking sector in general, no explanation has yet come out of Omaha.

Buffett turned 94 on Friday. As of June 30, Berkshire’s cash holdings hit a record $277 billion.