AC50 pilot reported a runway excursion resulted during landing roll out due to runway icing.

Narrative

I ran into heavy freezing rain and icing on approach to Runway XX; the TKS (Aircraft Deicing System) handled airframe icing normal; windshield deicing became minimal. there was a strong north crosswind on landing. Slowing to a taxi speed with the crosswind on a glazed iced runway; the steering became nil at slow speed and the aircraft slowly drifted off the edge of the runways landing surface. Braking effectiveness became nil. Aircraft slid slowly sideways after rudder control at a low taxi speed became ineffective.TKS required continuous use from MLI and was at 3 gallons remaining on approach. It was safer to land in these conditions; than attempt a flight on with minimal deicing TKS fluid remaining; while in moderate to heavy icing. Windshield became 80% iced over precluding adequate visibility to circle to Runway XY. Tower reported braking action 5 good.No aircraft damage occurred; and nothing was struck; just simply had a drifting excursion off the side of the runways main tarmac. Did not get into soft soil and was on reinforced tarmac edge. After inspection while parked; then with the assistance of airport personnel; I was able to restart and slowly exit the runway and taxi onto the ramp.