Walmart has topped the 68th edition of the Fortune 500 ranking of America's largest companies, with $572 billion revenue. It is followed by Amazon and Apple, with $469 billion and $365 billion revenue respectively. The list also features CVS Health, UnitedHealth Group and Exxon Mobil. Berkshire Hathaway, Alphabet, McKesson and AmerisourceBergen are the other companies in the top 10.