Nigerian billionaire Aliko Dangote, Africa’s richest person and the world’s 59th-richest, was one of only 12 billionaires among the 400 to increase their fortunes on the day, rising $180 million to $15.3 billion. The collective decline for the billionaires amounted to a fall of more than 1.5 percent. The combined loss is more than the market capitalization of Ford Motor Co. or Twenty-First Century Fox Inc. The S&P fell 2.1 percent on the day and the NASDAQ dropped 2.4 percent.