Warren Buffett has donated another huge slice of his sprawling wealth.
As in the past, the stock went to the Bill & Melinda Gates Foundation, as well as four foundations with ties to the Buffett family: Buffett's education-focused charity, which is named after his late wife Susan; the Sherwood Foundation, which is chaired by their daughter; the Howard G. Buffett Foundation, which is led by his son; and the NoVo Foundation, run by Buffett's youngest son Peter and his wife Jennifer.
Including the donation announced Monday, Buffett has now given $31 billion to these groups.
In 2006, Buffett announced plans to gradually donate all his Berkshire shares.
Since then, he's encouraged other wealthy people to focus on philanthropy, too.