Wal-Mart also announced a $20 billion share buyback but the drop in its share price wiped out close to the same amount in market value, and the intra-day low of $60.18 put the stock on track for its worst one-day performance in more than 17 years. Wal-Mart faces tough competition on multiple fronts, from the relentless expansion of online leader Amazon.com Inc to dollar stores and supermarkets fighting for a piece of Wal-Mart’s grocery business, which accounts for more than half of its U.S. sales. The company said it now expected earnings per share to decline by 6-12 percent next fiscal year.