There are 45 American families worth at least $10 billion, and the richest one is wealthier than Elon Musk. Walmart founder Sam Walton's heirs still own about 45% of the retail giant, giving them a combined net worth of $267 billion as of January 16, a new Forbes ranking of decabillionaire families shows. That figure dwarfs the Tesla and SpaceX CEO's net worth of about $202 billion. The 45 super-rich families are collectively worth about $1.3 trillion, or roughly 10 times Warren Buffett's personal fortune, as estimated by Forbes.