About 35 miles southeast of the destination airport, the pilot obtained the local weather information and requested the instrument landing system approach (ILS) to runway 31. Upon descending to the decision height, the pilot saw the runway end identifier lights and continued the approach. The pilot then saw the visual approach slope indicator lights and the runway lights and decided to land. The airplane touched down about 1,000 feet down the 5,100-foot-long runway. The pilot reported that when the tires came in contact with the runway, the brakes alternately skidded then "grabbed" the runway surface. The pilot decided not to go around and to remain on the runway and attempt to stop the airplane. The airplane traveled into the snow-covered terrain off the departure end of the runway where it contacted an ILS antenna pylon, resulting in substantial damage to the left wing spar. The pilot reported that the downsloping runway was ice covered and that he landed with an approximate 8-knot tailwind. He reported no preimpact mechanical failures or malfunctions with the airplane that would have precluded normal operation. He also stated he had no prior knowledge of what the braking action on the runway would be.