At least 40 major U.S. companies have substantial exposure to Venezuela's deepening economic crisis, and could collectively be forced to take billions of dollars of write downs, a Reuters analysis shows. The companies, all members of the S&P 500, and including some of the biggest names in Corporate America such as autos giant General Motors and drug maker Merck & Co Inc, together carry at least $11 billion of monetary assets in the Venezuelan currency, the bolivar, on their books.