Pilatus PC24 Captain reported a runway excursion during landing roll due to lack of surface braking action.

Narrative

We were landing ZZZ; no runway condition ratings were posted and no braking action was NOTAMed. On short final an airport employee stated on the UNICOM that the runway was clear but there was some ice. There was extensive ZZZ experience among the flight crew and the statement didn't seem alarming to either myself or the SIC.The final approach phase was normal and on glidepath for the visual; the aircraft was on speed and touched down in the touchdown zone; upon touchdown positive braking action was noted. Upon reaching the '2;000 feet remaining' point we noticed the braking action had dramatically decreased. With '500 feet remaining' we had slowed considerably but it was apparent we may not be able to completely stop. The airplane departed the end of the runway at an approximate speed of 10-15 knots into knee deep snow. Stopped about an airplane length off the end of the runway.Towed the airplane to the ramp after clearing the snow with no apparent damage following an extensive pre-flight inspection. Flew away the next morning and repositioned to ZZZ1 where the owner requested I have the airplane inspected.I feel the lack of a braking action report and an official runway condition report were key factors.