Exxon Mobil Corp. was stripped Tuesday of the perfect triple-A credit rating it has held for more than six decades by Standard & Poor’s Ratings Services, a sign that the oil bust is hurting even the strongest players in the energy industry. S&P downgraded Exxon Mobil by one notch to AA-plus. The world’s largest publicly traded oil company, Exxon, was just one of three American companies—Microsoft Corp. and Johnson & Johnson are the others—that had the triple-A rating. S&P said it first gave the company the triple-A mark in 1949. A representative for Exxon said it had been triple-A since 1930, counting its predecessor companies. But the company’s willingness to go into debt to fund its capital spending and keep paying out dividends even as oil prices plunged from highs of over $100 a barrel to as low as $26 has taken a toll on its balance sheet . […]