DETROIT — General Motors Co. is likely to file paperwork next week that describes its plan to sell shares to the public, a person familiar with the matter said Friday. The Detroit automaker had planned to file the papers on Friday but delayed the move to build distance between the filing and two major announcements it made on Thursday, said the person, who asked not to be identified because the company is not commenting publicly on the stock sale. GM said Thursday that CEO Edward Whitacre would step down as CEO Sept.