Facebook co-founder Mark Zuckerberg and his wife Dr. Priscilla Chan have announced they will give away 99 percent of their Facebook shares, currently worth $45 billion, to charity during their lifetimes. The announcement came in an open letter to their newborn daughter, Max. Meanwhile, a new report shows the 20 richest people in the United States own more wealth than half of the population of the U.S. combined. The report, published by Chuck Collins and Josh Hoxie of the Institute for Policy Studies, shows the top 20 wealthiest Americans, which includes Zuckerberg, own about $732 billion. The report also shows that the 100 richest households in the U.S. have the same amount of wealth as all African Americans in the United States combined.