WASHINGTON, Dec. 14 - Retirees who receive health benefits from their former employers saw premiums shoot up an average of 25 percent this year, a new study says. The study, issued Tuesday by the Kaiser Family Foundation and Hewitt Associates, showed a continued erosion of retiree health benefits among large employers. Companies are requiring retirees to pay a larger share of premiums and other health costs. While continuing to provide coverage for people who have already retired, about 8 percent of large private employers took action in the last year to end all subsidized health benefits for future retirees, and...